Chemical Coordination and Integration in Class 11 Biology Free Study Material in PDF
VavaClasses
225 views
145 slides
Apr 15, 2024
Slide 1 of 145
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
About This Presentation
Chemical coordination and integration are crucial processes in living organisms, including humans, facilitating communication and regulation among various body systems. In the human body, this coordination primarily occurs through the endocrine system, which comprises glands that secrete hormones. T...
Slide Content
UNIT 1 - NERVOUS SYSTEM I
UNIT 2 - NERVOUS SYSTEM II
UNIT 3 - NERVOUS SYSTEM III
UNIT 4 - ENDOCRINE SYSTEM I
UNIT 5 - ENDOCRINE SYSTEM II
HUMAN PHYSIOLOGY: NEURAL CONTROL AND
COORDINATION, CHEMICAL CONTROL AND
INTEGRATION
UNIT 2 - NERVOUS SYSTEM II
UNIT 3 - NERVOUS SYSTEM III
UNIT 4 - ENDOCRINE SYSTEM I
UNIT 5 - ENDOCRINE SYSTEM II
HUMAN PHYSIOLOGY: NEURAL CONTROL AND
COORDINATION, CHEMICAL CONTROL AND
INTEGRATION
3
1.1 INTRODUCTION TO THE NERVOUS SYSTEM
The nervous system is specialized for communication of information from one part of the body to
another. The nervous system communicates quickly using neurons, the specialized cells of the
nervous system. Neurons can convey and process information using electrical and chemical signals.
Ultimately, neural communication helps coordinate body activities and ensures we maintain
homeostasis.
The general functions of the nervous system are listed below:
The nervous system detects changes in our internal and external environment (stimuli) using
specific neurons or specialized cells communicating with neurons called sensory receptors.
Sensory receptors transform stimuli into electrical signals that our nervous system can
understand. Sensory neurons transmit the electrical signals from the periphery to the central
nervous system (Brain and spinal cord).
The central nervous system (brain and spinal cord) processes incoming sensory information
to generate “appropriate” responses and also to give us the perception of the stimulus.
The central nervous system sends commands (electrical signals passed along neurons) out
to the target tissues to produce the response.
Cranial nerves
Peripheral
nervous
system
Brain
Central
nervous
system
Spinal
cord
Spinal nerves
Autonomic nervous system ganglia
The nervous system consists of two major divisions:
1. The central nervous system (CNS) consists of the brain and the spinal cord, which are
enclosed in the skull and vertebral column, respectively.
2. The peripheral nervous system (PNS) consists of all the neural tissue outside of the brain
and spinal cord. The PNS includes the cranial nerves and spinal nerves, sensory receptors
and ganglia (cell bodies (somas) of neurons that lie outside the CNS). The nerves connect all
other part of the body with the CNS.
UNIT 1 - NERVOUS TISSUE I
1.1 INTRODUCTION TO THE NERVOUS SYSTEM
The nervous system is specialized for communication of information from one part of the body to
another. The nervous system communicates quickly using neurons, the specialized cells of the
nervous system. Neurons can convey and process information using electrical and chemical signals.
Ultimately, neural communication helps coordinate body activities and ensures we maintain
homeostasis.
The general functions of the nervous system are listed below:
The nervous system detects changes in our internal and external environment (stimuli) using
specific neurons or specialized cells communicating with neurons called sensory receptors.
Sensory receptors transform stimuli into electrical signals that our nervous system can
understand. Sensory neurons transmit the electrical signals from the periphery to the central
nervous system (Brain and spinal cord).
The central nervous system (brain and spinal cord) processes incoming sensory information
to generate “appropriate” responses and also to give us the perception of the stimulus.
The central nervous system sends commands (electrical signals passed along neurons) out
to the target tissues to produce the response.
Cranial nerves
Peripheral
nervous
system
Brain
Central
nervous
system
Spinal
cord
Spinal nerves
Autonomic nervous system ganglia
The nervous system consists of two major divisions:
1. The central nervous system (CNS) consists of the brain and the spinal cord, which are
enclosed in the skull and vertebral column, respectively.
2. The peripheral nervous system (PNS) consists of all the neural tissue outside of the brain
and spinal cord. The PNS includes the cranial nerves and spinal nerves, sensory receptors
and ganglia (cell bodies (somas) of neurons that lie outside the CNS). The nerves connect all
other part of the body with the CNS.
UNIT 1 - NERVOUS TISSUE I
4
The peripheral nervous system has several subdivisions. It is first divided based on function into
sensory (afferent) and motor (efferent) divisions. Each of these is further subdivided into somatic
and autonomic (visceral) divisions.
The includes
the brain and the spinal cord. which are
enclosed in the skull and vertebral column,
respectively. The CNS is connected to all
other parts of the body by the PNS nerves.
central nervous system (CNS)
The of sensory
information, sometimes with higher cognitive
functions to become a conscious perception, may
then lead to either a conscious or subconscious
motor response
central integration
Peripheral Nervous system
peripheral nervous system (PNS) The
consists of all neural tissue outside of the
brain and spinal cord. The PNS includes the cranial nerves and spinal nerves, sensory receptors and ganglia (cell
bodies of neurons that lie outside the
CNS). The PNS brings sensory
information to the CNS or carries motor
output from the CNS to initiate a reaction.
The of the PNS contains
nerves carrying sensory information into the
CNS. The sensory neurons in the sensory or
mixed nerves are also called afferents.
sensory division
The , more commonly
called the autonomic nervous system, controls
the action of cardiac muscle, smooth muscle,
and glands. The responses in these targets
are usually involuntary. Body processes
controlled by the autonomic nervous system
include the contractions of the stomach and
other digestive organs, the heart rate, and
contractions of blood vessels to control blood
pressure and flow though the body.
visceral motor division
The of the PNS contains nerves carrying
information out of the CNS to target organs. The motor
neurons in the motor of mixed nerves are also called efferents.
motor division
The
controls
the voluntary action
of the skeletal
muscles in the body.
The responses in these targets are usually voluntary.
somatic motor
division
Includes
The or conduct
signats predominantly from organs contained in the
thoracic and abdominopelvic cavities (ex. heart, lungs, intestines. bladder, etc). Visceral receptors detect chunges in the chemical environment of body fluids and state of internal organs, such as pressure and stretch.
visceral autonomic sensory receptors
The contains neurons located in the
walls of the digestive tract. Some scientists view the
enteric nervous system as a completely independent part
of the nervous system akin to the CNS and PNS since it can function independently to generate gland secretion
and some aspects of motility and is anatomically discrete.
Other scientists classify the enteric nervous system as a
subdivision of the motor arm of the PNS because it
innervates the same type of effectors (muscles and
glands) the scheme we will use here.
enteric division
Receptors can be neurons, cells of specialized
structures. They monitor and detect changes
to the body`s internal or external environment.
Skeletal muscle
The
are widely distributed
throughout body tissues. They are located in, and sense
information from the structures
of the skin, muscles, and joints
(including the related structures
of tendons and ligaments).
These somatic senses include
gustation, olfaction, hearing,
equilibrium and vision.somatic sensory
receptors
The of
are
found in specialized
organs localized in the
head. These special senses include smell,
taste, sight, hearing
and equilibrium.
receptors
special senses
The
mobilizes body
systems during activity
(‘flight or fight’). It
controls functions that
speed up the heart and increase energy usage during emergencies or
times of stress.
sympathetic
division
The
promotes ‘housekeeping’
functions (‘rest and digest’). It
controls functions that have the
opposite effect to reduce heart
rate and decrease overall
energy usage when the body is
returning to normal after an
emergency or during normal
functioning.
parasympathetic division
Start
Effectors are muscles or glands. that respond to moto
nerve impulses.
4
3
2
1
5
The peripheral nervous system has several subdivisions. It is first divided based on function into
sensory (afferent) and motor (efferent) divisions. Each of these is further subdivided into somatic
and autonomic (visceral) divisions.
The includes
the brain and the spinal cord. which are
enclosed in the skull and vertebral column,
respectively. The CNS is connected to all
other parts of the body by the PNS nerves.
central nervous system (CNS)
The of sensory
information, sometimes with higher cognitive
functions to become a conscious perception, may
then lead to either a conscious or subconscious
motor response
central integration
Peripheral Nervous system
peripheral nervous system (PNS) The
consists of all neural tissue outside of the
brain and spinal cord. The PNS includes the cranial nerves and spinal nerves, sensory receptors and ganglia (cell
bodies of neurons that lie outside the
CNS). The PNS brings sensory
information to the CNS or carries motor
output from the CNS to initiate a reaction.
The of the PNS contains
nerves carrying sensory information into the
CNS. The sensory neurons in the sensory or
mixed nerves are also called afferents.
sensory division
The , more commonly
called the autonomic nervous system, controls
the action of cardiac muscle, smooth muscle,
and glands. The responses in these targets
are usually involuntary. Body processes
controlled by the autonomic nervous system
include the contractions of the stomach and
other digestive organs, the heart rate, and
contractions of blood vessels to control blood
pressure and flow though the body.
visceral motor division
The of the PNS contains nerves carrying
information out of the CNS to target organs. The motor
neurons in the motor of mixed nerves are also called efferents.
motor division
The
controls
the voluntary action
of the skeletal
muscles in the body.
The responses in these targets are usually voluntary.
somatic motor
division
Includes
The or conduct
signats predominantly from organs contained in the
thoracic and abdominopelvic cavities (ex. heart, lungs, intestines. bladder, etc). Visceral receptors detect chunges in the chemical environment of body fluids and state of internal organs, such as pressure and stretch.
visceral autonomic sensory receptors
The contains neurons located in the
walls of the digestive tract. Some scientists view the
enteric nervous system as a completely independent part
of the nervous system akin to the CNS and PNS since it can function independently to generate gland secretion
and some aspects of motility and is anatomically discrete.
Other scientists classify the enteric nervous system as a
subdivision of the motor arm of the PNS because it
innervates the same type of effectors (muscles and
glands) the scheme we will use here.
enteric division
Receptors can be neurons, cells of specialized
structures. They monitor and detect changes
to the body`s internal or external environment.
Skeletal muscle
The
are widely distributed
throughout body tissues. They are located in, and sense
information from the structures
of the skin, muscles, and joints
(including the related structures
of tendons and ligaments).
These somatic senses include
gustation, olfaction, hearing,
equilibrium and vision.somatic sensory
receptors
The of
are
found in specialized
organs localized in the
head. These special senses include smell,
taste, sight, hearing
and equilibrium.
receptors
special senses
The
mobilizes body
systems during activity
(‘flight or fight’). It
controls functions that
speed up the heart and increase energy usage during emergencies or
times of stress.
sympathetic
division
The
promotes ‘housekeeping’
functions (‘rest and digest’). It
controls functions that have the
opposite effect to reduce heart
rate and decrease overall
energy usage when the body is
returning to normal after an
emergency or during normal
functioning.
parasympathetic division
Start
Effectors are muscles or glands. that respond to moto
nerve impulses.
4
3
2
1
5
5
The
nerves that comprise the peripheral nervous system can be divided into two divisions based on
whether information is travelling into the CNS or information is leaving the CNS. The sensory
division of the PNS contains nerves carrying sensory information into the CNS. These sensory
nerves are also called afferents (carrying toward). The motor division contains nerves carrying
information out of the CNS to target organs. These motor nerves are also called efferent (carrying
away).
The sensory (afferent) division of the PNS has two subdivisions. The somatic sensory division
conducts signals from receptors located in the skeletal muscles and skin. The visceral or autonomic
sensory division conducts signals predominantly from organs contained in the thoracic and
abdominopelvic cavities (eg. heart, lungs, intestine, bladder etc).
The motor (efferent) division of the PNS is also subdivided into somatic and visceral divisions. The
somatic motor division controls the voluntary actions of the skeletal muscles in the body. The
visceral motor division, more commonly called the autonomic nervous system, controls the
action of cardiac muscle, smooth muscle and glands. The responses in these targets are usually
involuntary.
The autonomic nervous system (ANS) is further subdivided into the sympathetic divisions and the
parasympathetic division. Generally, the sympathetic division is involved in getting the body ready
to respond to a physical challenge or an emotional threat, classified historically as the “fight or flight”
division of the ANS. The parasympathetic division functions in opposition to the sympathetic nervous
system. It is responsible for “rest and digest” activities, and is involved in salivation, digestion,
urination and defecation.
1.2 NERVOUS TISSUE
Salient features
Originates from the ectoderm.
Specialized for receiving stimuli, transmit message (conductivity) and coordination by which
two or more organs interact and complement the functions of one another.
Divided into neurons (nerves) and neuroglia.
1.2.1 Neurons
Neurons are considered the simplest functional unit of nervous tissue. They are long lived (most live
for your entire life), electrically active cells that consume a lot of energy. Neurons are capable of
responding to stimulation, conducting electrical signals, and secreting chemicals that allow them to
communicate with other cells. They cannot usually regenerate if damaged since most neurons do
not retain the ability to divide, as centriole is absent or immaturely present.
Neurons have anatomically and functionally distinct regions for receiving, integrating and sending
information from one part of the body to another.
The
nerves that comprise the peripheral nervous system can be divided into two divisions based on
whether information is travelling into the CNS or information is leaving the CNS. The sensory
division of the PNS contains nerves carrying sensory information into the CNS. These sensory
nerves are also called afferents (carrying toward). The motor division contains nerves carrying
information out of the CNS to target organs. These motor nerves are also called efferent (carrying
away).
The sensory (afferent) division of the PNS has two subdivisions. The somatic sensory division
conducts signals from receptors located in the skeletal muscles and skin. The visceral or autonomic
sensory division conducts signals predominantly from organs contained in the thoracic and
abdominopelvic cavities (eg. heart, lungs, intestine, bladder etc).
The motor (efferent) division of the PNS is also subdivided into somatic and visceral divisions. The
somatic motor division controls the voluntary actions of the skeletal muscles in the body. The
visceral motor division, more commonly called the autonomic nervous system, controls the
action of cardiac muscle, smooth muscle and glands. The responses in these targets are usually
involuntary.
The autonomic nervous system (ANS) is further subdivided into the sympathetic divisions and the
parasympathetic division. Generally, the sympathetic division is involved in getting the body ready
to respond to a physical challenge or an emotional threat, classified historically as the “fight or flight”
division of the ANS. The parasympathetic division functions in opposition to the sympathetic nervous
system. It is responsible for “rest and digest” activities, and is involved in salivation, digestion,
urination and defecation.
1.2 NERVOUS TISSUE
Salient features
Originates from the ectoderm.
Specialized for receiving stimuli, transmit message (conductivity) and coordination by which
two or more organs interact and complement the functions of one another.
Divided into neurons (nerves) and neuroglia.
1.2.1 Neurons
Neurons are considered the simplest functional unit of nervous tissue. They are long lived (most live
for your entire life), electrically active cells that consume a lot of energy. Neurons are capable of
responding to stimulation, conducting electrical signals, and secreting chemicals that allow them to
communicate with other cells. They cannot usually regenerate if damaged since most neurons do
not retain the ability to divide, as centriole is absent or immaturely present.
Neurons have anatomically and functionally distinct regions for receiving, integrating and sending
information from one part of the body to another.
6
Neurofibril
Nucleus of
Schwann cell
Myelin sheath
Neurilemma of
Schwann cell
Axon or axis
cylinder
Axolemma
Node of Ranvier
Telodendria
Cytoplasm
Cell body or
perikaryon
Axon hillock
Dendrites
Axon collateral
Axon or axis
cylinder
Myelin sheath
of schwann cell
Nucleus of
schwann cell
Node of
Ranvier
Neurilemma of
schwann cell
A. Components of neurons
A typical neuron, like that shown above, has two distinct processes or cytoplasmic extensions on
either side of a soma (cell body). On one side of the soma are short, tapering processes called
dendrites (greek denderon – tree). Most neurons have many, highly branched dendrites, although
they may have as few as one. Dendrites receive information from other neurons and transfer it to
the cell body. The greater the number of dendrites, the more information the neuron can collect to
use during decision making.
The soma (cell body) is the region of the neuron that integrates all the incoming information from
the dendrites. The cell body is somewhat spherical in shape and for humans, typically ranges in size
from 5 to 100 microns in diameter. The some contains the neuron’s nucleus and housekeeping
organelles (eg. mitochondria, lysosomes, golgi complex, rough endoplasmic reticulum, etc). The
soma is the only site in a neuron that can synthesize proteins, neurotransmitters, or materials needed
for cell maintenance and repair. ER and ribosome form granules like structure called Nissl’s granules
or Tigroid body, it is here the proteins are actually synthesized in soma. Neurofibrils found in the
cytoplasm help in internal conduction in the soma.
Neurofibril
Nucleus of
Schwann cell
Myelin sheath
Neurilemma of
Schwann cell
Axon or axis
cylinder
Axolemma
Node of Ranvier
Telodendria
Cytoplasm
Cell body or
perikaryon
Axon hillock
Dendrites
Axon collateral
Axon or axis
cylinder
Myelin sheath
of schwann cell
Nucleus of
schwann cell
Node of
Ranvier
Neurilemma of
schwann cell
A. Components of neurons
A typical neuron, like that shown above, has two distinct processes or cytoplasmic extensions on
either side of a soma (cell body). On one side of the soma are short, tapering processes called
dendrites (greek denderon – tree). Most neurons have many, highly branched dendrites, although
they may have as few as one. Dendrites receive information from other neurons and transfer it to
the cell body. The greater the number of dendrites, the more information the neuron can collect to
use during decision making.
The soma (cell body) is the region of the neuron that integrates all the incoming information from
the dendrites. The cell body is somewhat spherical in shape and for humans, typically ranges in size
from 5 to 100 microns in diameter. The some contains the neuron’s nucleus and housekeeping
organelles (eg. mitochondria, lysosomes, golgi complex, rough endoplasmic reticulum, etc). The
soma is the only site in a neuron that can synthesize proteins, neurotransmitters, or materials needed
for cell maintenance and repair. ER and ribosome form granules like structure called Nissl’s granules
or Tigroid body, it is here the proteins are actually synthesized in soma. Neurofibrils found in the
cytoplasm help in internal conduction in the soma.
7
Axoplasm of axon contains only neurofibrils and mitochondria, no Nissl’s granules. Axon is covered
by axolemma. The terminal end of axon is branched in button shape branches called telodendria.
More mitochondria are found in the telodendria which synthesize acetylcholine (Ach, stored in the
vesicles) with the help of choline acetyl transferase enzyme. Axon is covered by a layer of
phospholipids (sphingomyelin) which is called as medulla or myelin sheath. Medulla is covered by
thin cell membrane, called as neurilemma composed of schwann cells. These schwann cells take
part in the deposition of myelin sheath (myelinogenesis) which acts as an insulator and prevents
leakage of ions.
The axon functions like a cable, relaying electrical signals away from the cell body towards other
neurons or cells (eg. muscles, glands). Axons are also called nerve fibers. The axon has three
regions. As it emerges from the cell body, the axon forms a structure called the axon hillock, a
tapered region that contains the initial segment, or trigger zone, where propagating electrical
signals called action potentials are initiated or generated. The next part of the axon is the longest,
typically a single, thin (.5 to 3 microns), almost constant diameter process that extends to a target.
Axons can be long, short or in between.
Myelinogenesis in the peripheral nervous system (PNS)
In the peripheral nerves, myelinogenesis begins with the deposition of myelin sheath in concentric
layer around the axon by schwann cells. Myelin sheath is discontinuous around the axon. These
interruptions where axon is uncovered by myelin sheath are called nodes of Ranvier.
Myelinogenesis in the central nervous system (CNS)
Neurilemma or schwann cells are not present therefore myelinogenesis process occurs with the
help of oligodendrocytes (neuroglia). Neurons in which myelin sheath is present, are called
medullated or myelinated neurons. In some nerve cells myelin sheath is absent, called as non
mdedullated or non myelinated neurons.
The axon may travel to its target as a single fiber, but some axons form branches called collaterals,
so that they can interact with not just one, but many target cells. The third region of the axon is found
when it reaches its target. Here the axon branches extensively forming the synaptic terminals
(terminal arborization). Each branch ends with a small swelling called a synaptic knob, which
contains vesicles filled with chemical messengers (neurotransmitters) that conduct the signal to
the next cell.
TARGET POINTS
Axon Dendron
Always single One or more
Has neurofibrils but no Nissl’s granules Has both
Long sized process Small sized
Nerve impulse travels away from the cell Nerve impulse travels towards the cell body
body (centrifugal) (centripetal)
Axoplasm of axon contains only neurofibrils and mitochondria, no Nissl’s granules. Axon is covered
by axolemma. The terminal end of axon is branched in button shape branches called telodendria.
More mitochondria are found in the telodendria which synthesize acetylcholine (Ach, stored in the
vesicles) with the help of choline acetyl transferase enzyme. Axon is covered by a layer of
phospholipids (sphingomyelin) which is called as medulla or myelin sheath. Medulla is covered by
thin cell membrane, called as neurilemma composed of schwann cells. These schwann cells take
part in the deposition of myelin sheath (myelinogenesis) which acts as an insulator and prevents
leakage of ions.
The axon functions like a cable, relaying electrical signals away from the cell body towards other
neurons or cells (eg. muscles, glands). Axons are also called nerve fibers. The axon has three
regions. As it emerges from the cell body, the axon forms a structure called the axon hillock, a
tapered region that contains the initial segment, or trigger zone, where propagating electrical
signals called action potentials are initiated or generated. The next part of the axon is the longest,
typically a single, thin (.5 to 3 microns), almost constant diameter process that extends to a target.
Axons can be long, short or in between.
Myelinogenesis in the peripheral nervous system (PNS)
In the peripheral nerves, myelinogenesis begins with the deposition of myelin sheath in concentric
layer around the axon by schwann cells. Myelin sheath is discontinuous around the axon. These
interruptions where axon is uncovered by myelin sheath are called nodes of Ranvier.
Myelinogenesis in the central nervous system (CNS)
Neurilemma or schwann cells are not present therefore myelinogenesis process occurs with the
help of oligodendrocytes (neuroglia). Neurons in which myelin sheath is present, are called
medullated or myelinated neurons. In some nerve cells myelin sheath is absent, called as non
mdedullated or non myelinated neurons.
The axon may travel to its target as a single fiber, but some axons form branches called collaterals,
so that they can interact with not just one, but many target cells. The third region of the axon is found
when it reaches its target. Here the axon branches extensively forming the synaptic terminals
(terminal arborization). Each branch ends with a small swelling called a synaptic knob, which
contains vesicles filled with chemical messengers (neurotransmitters) that conduct the signal to
the next cell.
TARGET POINTS
Axon Dendron
Always single One or more
Has neurofibrils but no Nissl’s granules Has both
Long sized process Small sized
Nerve impulse travels away from the cell Nerve impulse travels towards the cell body
body (centrifugal) (centripetal)
8
B. Types of neurons
(i) Functional classification
Functional classification of neurons is based on the direction of information flow along axons relative
to the CNS. Based on this criterion, there are 3 types of neurons: sensory neurons, interneurons,
and motor neurons.
Sensory (afferent) neurons are specialized for detection of sensory information (eg. light, pressure,
vibration, temperature, chemicals etc). They transduce physical and chemical stimuli into electrical
signals and transfer this information from the periphery towards the central nervous system for
processing. In many cases, sensory neurons have their dendrites, soma and a part of their axon
residing outside the CNS with axon terminals forming connections (synapses) with other neurons
within the CNS.
Interneurons (association neurons) are located entirely within the central nervous system (with
the dendrites, soma and axons of the cell all residing within the CNS). Interneurons are also referred
to as association neurons, in part because they are sandwiched between sensory and motor neurons
where they integrate and distribute sensory information and coordinate motor output. Interneurons
account for 90% of all neurons of the CNS and therefore are the most numerous neurons in the
body. Almost all interneurons are multipolar.
Motor (efferent) neurons carry impulses or motor commands away from the central nervous system
to effectors/ target organs (eg. muscles and glands). Most motor neurons have dendrites and cell bodies
in the CNS and axons that exit the CNS to form peripheral nerves that travel to effectors (targets).
Posterior root
ganglion
Cell body
of sensory
neuron
Afferent
(input)
transmission
Spinal cord
Dendrites
Sensory neuron
Efferent
(output)
transmission
Motor neuron
Axon
Interneuron
Input
Output
Effectors (muscles and glands)
Receptors
Associative area: The cerebral cortex contains motor area, sensory area and large area (regions)
called associative area responsible for complex function like inter sensory association, memory and
communication.
(ii) Structural classification
The structural classification of neurons is based on the number of processes that extend from the
soma. There are 4 basic neuronal structures like those shown in the figure below though there are
many subtle variations on each theme.
B. Types of neurons
(i) Functional classification
Functional classification of neurons is based on the direction of information flow along axons relative
to the CNS. Based on this criterion, there are 3 types of neurons: sensory neurons, interneurons,
and motor neurons.
Sensory (afferent) neurons are specialized for detection of sensory information (eg. light, pressure,
vibration, temperature, chemicals etc). They transduce physical and chemical stimuli into electrical
signals and transfer this information from the periphery towards the central nervous system for
processing. In many cases, sensory neurons have their dendrites, soma and a part of their axon
residing outside the CNS with axon terminals forming connections (synapses) with other neurons
within the CNS.
Interneurons (association neurons) are located entirely within the central nervous system (with
the dendrites, soma and axons of the cell all residing within the CNS). Interneurons are also referred
to as association neurons, in part because they are sandwiched between sensory and motor neurons
where they integrate and distribute sensory information and coordinate motor output. Interneurons
account for 90% of all neurons of the CNS and therefore are the most numerous neurons in the
body. Almost all interneurons are multipolar.
Motor (efferent) neurons carry impulses or motor commands away from the central nervous system
to effectors/ target organs (eg. muscles and glands). Most motor neurons have dendrites and cell bodies
in the CNS and axons that exit the CNS to form peripheral nerves that travel to effectors (targets).
Posterior root
ganglion
Cell body
of sensory
neuron
Afferent
(input)
transmission
Spinal cord
Dendrites
Sensory neuron
Efferent
(output)
transmission
Motor neuron
Axon
Interneuron
Input
Output
Effectors (muscles and glands)
Receptors
Associative area: The cerebral cortex contains motor area, sensory area and large area (regions)
called associative area responsible for complex function like inter sensory association, memory and
communication.
(ii) Structural classification
The structural classification of neurons is based on the number of processes that extend from the
soma. There are 4 basic neuronal structures like those shown in the figure below though there are
many subtle variations on each theme.
9
Bipolar neurons have a single dendrite extending from one side of the cell body and a single axon
extending from the other side. Bipolar neurons are small cells, typically extending for less than 30
microns from dendrite to axon terminal. There are not many true bipolar cells in the body. A few
examples are found in the special sense organs for vision and olfaction (smell).
Unipolar or pseudounipolar neurons have a single process that emanates from the cell body. The
single process has dendrites on one end and the rest of the process is an axon. Most sensory neurons
of the peripheral nervous system are unipolar neurons. The dendrites are located in the periphery,
where stimuli are detected. The sensory information travels on the dendrite towards the soma (usually
located ganglia just outside the CNS). The axon stretches into the CNS at the spinal cord.
Multipolar neurons have two or more dendrites on one side and a single axon on the other side of
the soma. Multipolar neurons are the most common neurons in the CNS. One example are motor
neurons which have dendrites and somas located in the spinal cord and axons that leave the CNS
to innervate skeletal muscles.
Anaxonic neurons are small, stellate (star shaped) cells with processes that all look alike with no
apparent axon. Anaxonic neurons can be found in the central nervous system, the retina, and in the
adrenal medulla. Their functions are not well understood.
Apolar/ nonpolar neuron: No definite Dendron/ axon. Cell process are either
absent or if present are not differentiated in axon and dendrons. Nerve impulse
radiates in all directions. eg. hydra, amacrine cells of retina, horizontal neuron cell.
Motor neuron
Dendrites
Pyramidal neuron
Dendrites
Purkinje cell
Axon Axon
Multipolar neurons
Bipolar neurons
Retinal neuronOlfactory neuron
Unipolar neuron
(touch and pain sensory neuron)
Dendrites
Axon
Dendrites Axon
Anaxonic neuron
(Amacrine cell)
Dendrites
Apolar neuron
Bipolar neurons have a single dendrite extending from one side of the cell body and a single axon
extending from the other side. Bipolar neurons are small cells, typically extending for less than 30
microns from dendrite to axon terminal. There are not many true bipolar cells in the body. A few
examples are found in the special sense organs for vision and olfaction (smell).
Unipolar or pseudounipolar neurons have a single process that emanates from the cell body. The
single process has dendrites on one end and the rest of the process is an axon. Most sensory neurons
of the peripheral nervous system are unipolar neurons. The dendrites are located in the periphery,
where stimuli are detected. The sensory information travels on the dendrite towards the soma (usually
located ganglia just outside the CNS). The axon stretches into the CNS at the spinal cord.
Multipolar neurons have two or more dendrites on one side and a single axon on the other side of
the soma. Multipolar neurons are the most common neurons in the CNS. One example are motor
neurons which have dendrites and somas located in the spinal cord and axons that leave the CNS
to innervate skeletal muscles.
Anaxonic neurons are small, stellate (star shaped) cells with processes that all look alike with no
apparent axon. Anaxonic neurons can be found in the central nervous system, the retina, and in the
adrenal medulla. Their functions are not well understood.
Apolar/ nonpolar neuron: No definite Dendron/ axon. Cell process are either
absent or if present are not differentiated in axon and dendrons. Nerve impulse
radiates in all directions. eg. hydra, amacrine cells of retina, horizontal neuron cell.
Motor neuron
Dendrites
Pyramidal neuron
Dendrites
Purkinje cell
Axon Axon
Multipolar neurons
Bipolar neurons
Retinal neuronOlfactory neuron
Unipolar neuron
(touch and pain sensory neuron)
Dendrites
Axon
Dendrites Axon
Anaxonic neuron
(Amacrine cell)
Dendrites
Apolar neuron
10
1.2.2 Glial cells
Most neurons are surrounded by glial cells (neuroglia), the other cell type found in the nervous
tissue. Glial cells are the supportive cells of the nervous system and are 10 times more numerous
than neurons. The most well defined role for neuroglia is to provide structure to the delicate nervous
tissue. They fill the space between neurons, serving as mortar or “glue” and thus hold nervous
tissue together. Unlike neurons, glial cells retain the ability to divide throughout one’s lifetime. When
neurons are injured, neuroglia are stimulated to divide and form glial scars. Glial cells have different
shapes and sizes and their processes are indistinguishable in contrast to the distinct axon and
dendrites found in neurons.
There are 6 types of glial cells, 4 types are found in the CNS and 2 types in the PNS. The CNS
neuroglia are: astrocytes; oligodendrocytes; microglia and ependymal cells. The 2 types of
glial cell found only in the peripheral nervous system (PNS) are satellite cells and schwann cells.
Glial cells
are found in
Peripheral nervous system Central nervous system
Contains
Satellite
cells
Schwann cells
Contains
Oligodendrocytes
Microglia (modified immune cells)
Astrocytes Ependymal cells
Myelin sheaths
Form Form
Scavengers
act as
Substrates for ATP productionBlood-brain barrier Neurotrophic
factors
K , water,
neurotransmittets
+
Source of
neural
stem cells
Barriers
between
compartments
Support cell bodies
Neurotrophic factors
ProvideSecrete Help formSecrete Take up Create
A. CNS glial cells
Astrocytes are star shaped neuroglia and are the most numerous cells in the central nervous
system. They make up half of all cells in the brain. Astrocytes provide a structurally supportive
framework for neurons with their processes wrapping most non synaptic regions of neurons in gray
matter and covering the entire outer surface of the brain to form the glial pia (connective tissue
meninx) interface. Astrocytes help form the protective blood brain barrier by encircling CNS capillary
1.2.2 Glial cells
Most neurons are surrounded by glial cells (neuroglia), the other cell type found in the nervous
tissue. Glial cells are the supportive cells of the nervous system and are 10 times more numerous
than neurons. The most well defined role for neuroglia is to provide structure to the delicate nervous
tissue. They fill the space between neurons, serving as mortar or “glue” and thus hold nervous
tissue together. Unlike neurons, glial cells retain the ability to divide throughout one’s lifetime. When
neurons are injured, neuroglia are stimulated to divide and form glial scars. Glial cells have different
shapes and sizes and their processes are indistinguishable in contrast to the distinct axon and
dendrites found in neurons.
There are 6 types of glial cells, 4 types are found in the CNS and 2 types in the PNS. The CNS
neuroglia are: astrocytes; oligodendrocytes; microglia and ependymal cells. The 2 types of
glial cell found only in the peripheral nervous system (PNS) are satellite cells and schwann cells.
Glial cells
are found in
Peripheral nervous system Central nervous system
Contains
Satellite
cells
Schwann cells
Contains
Oligodendrocytes
Microglia (modified immune cells)
Astrocytes Ependymal cells
Myelin sheaths
Form Form
Scavengers
act as
Substrates for ATP productionBlood-brain barrier Neurotrophic
factors
K , water,
neurotransmittets
+
Source of
neural
stem cells
Barriers
between
compartments
Support cell bodies
Neurotrophic factors
ProvideSecrete Help formSecrete Take up Create
A. CNS glial cells
Astrocytes are star shaped neuroglia and are the most numerous cells in the central nervous
system. They make up half of all cells in the brain. Astrocytes provide a structurally supportive
framework for neurons with their processes wrapping most non synaptic regions of neurons in gray
matter and covering the entire outer surface of the brain to form the glial pia (connective tissue
meninx) interface. Astrocytes help form the protective blood brain barrier by encircling CNS capillary
11
endothelial cells and stimulating the cells to form tight junctions. They help to maintain the
concentration of chemicals in the extracellular space and remove excess signaling molecules.
Astrocytes also react to neural tissue damage by forming scar tissue in the damaged space.
Oligodendrocytes are glial cells of the CNS that wrap and insulate axons and give the CNS white
matter its characteristic glossy, white appearance. Oligodendrocytes have a large soma with up to
15 processes. The processes reach out to axons of nearby neurons and wrap around them (like
wrapping tape around a pencil) forming a high resistance sheath called myelin. Myelin insulates a
small region of the axon (prevents ions from leaking out into the extracellular fluid), which facilitates
signal propagation down the axon towards the synaptic terminal. A single oligodendrocytes process
will wrap axons of numerous different neurons. Processes from many different oligodendrocytes
contribute to the myelin sheath of a single neuron’s axon.
Microglia are small highly mobile, phagocytic neuroglia that protect nervous tissue pathogen infection,
remove debris and waste, and may play a role in remodeling of the synapse that occurs during
development and with learning. About 10 – 15% of CNS glial cells are microglia. Microglia are
derived from monocytes and thus are more closely related to white blood cells than to the other glial
cells. Since cells of the immune system cannot penetrate the blood brain barrier, microglia serve as
brain macrophages, destroying foreign invaders, promoting inflammation and destroying cancer
cells and cells infected with virus. Clusters of microglia in nervous tissue provide pathologists with
evidence of recent injury.
Ependymal cells are cuboidal shaped glial cells that are joined together to form a continuous sheet
lining the fluid-filled ventricles and central canal of the brain and spinal cord. Ependymal cells produce
and secrete cerebrospinal fluid (CSF), the fluid that bathes the tissues of the CNS. The basal side
of the cell has rootlets that anchor the cells to the underlying tissue. The apical surface is marked by
cilia, which helps circulate the CSF.
B. PNS glial cells
The remaining two glial cells, schwann cells and satellite cells, are found solely in the peripheral
nervous system.
Schwann cells are analogous in function to oligodendrocytes (found in the CNS). They insulate the
axons of peripheral nerves in one of two ways. A schwann cell can wind its way round and round the
axon (up to 100 times), while squeezing its cytoplasm out of the way (much like a toothpaste tube
could be wrapped around a pencil), forming a myelin sheath. Like myelinating a single fiber in the
CNS, which requires many oligodendrocytes, a complete myelin sheath in the PNS requires many
schwann cells. Schwann cells can also envelop PNS axons without forming a myelin sheath. Instead
of wrapping a single axon many times, the schwann cell forms an envelope around a bundle of
unmyelinated axons.
Additionally, schwann cells can also assist in the regeneration of a damaged peripheral nerve. If a
peripheral nerve is damaged, it may regenerate if its soma is undamaged and the neurilemma (the
plasma membrane of the schwann cell) enveloping it is intact.
endothelial cells and stimulating the cells to form tight junctions. They help to maintain the
concentration of chemicals in the extracellular space and remove excess signaling molecules.
Astrocytes also react to neural tissue damage by forming scar tissue in the damaged space.
Oligodendrocytes are glial cells of the CNS that wrap and insulate axons and give the CNS white
matter its characteristic glossy, white appearance. Oligodendrocytes have a large soma with up to
15 processes. The processes reach out to axons of nearby neurons and wrap around them (like
wrapping tape around a pencil) forming a high resistance sheath called myelin. Myelin insulates a
small region of the axon (prevents ions from leaking out into the extracellular fluid), which facilitates
signal propagation down the axon towards the synaptic terminal. A single oligodendrocytes process
will wrap axons of numerous different neurons. Processes from many different oligodendrocytes
contribute to the myelin sheath of a single neuron’s axon.
Microglia are small highly mobile, phagocytic neuroglia that protect nervous tissue pathogen infection,
remove debris and waste, and may play a role in remodeling of the synapse that occurs during
development and with learning. About 10 – 15% of CNS glial cells are microglia. Microglia are
derived from monocytes and thus are more closely related to white blood cells than to the other glial
cells. Since cells of the immune system cannot penetrate the blood brain barrier, microglia serve as
brain macrophages, destroying foreign invaders, promoting inflammation and destroying cancer
cells and cells infected with virus. Clusters of microglia in nervous tissue provide pathologists with
evidence of recent injury.
Ependymal cells are cuboidal shaped glial cells that are joined together to form a continuous sheet
lining the fluid-filled ventricles and central canal of the brain and spinal cord. Ependymal cells produce
and secrete cerebrospinal fluid (CSF), the fluid that bathes the tissues of the CNS. The basal side
of the cell has rootlets that anchor the cells to the underlying tissue. The apical surface is marked by
cilia, which helps circulate the CSF.
B. PNS glial cells
The remaining two glial cells, schwann cells and satellite cells, are found solely in the peripheral
nervous system.
Schwann cells are analogous in function to oligodendrocytes (found in the CNS). They insulate the
axons of peripheral nerves in one of two ways. A schwann cell can wind its way round and round the
axon (up to 100 times), while squeezing its cytoplasm out of the way (much like a toothpaste tube
could be wrapped around a pencil), forming a myelin sheath. Like myelinating a single fiber in the
CNS, which requires many oligodendrocytes, a complete myelin sheath in the PNS requires many
schwann cells. Schwann cells can also envelop PNS axons without forming a myelin sheath. Instead
of wrapping a single axon many times, the schwann cell forms an envelope around a bundle of
unmyelinated axons.
Additionally, schwann cells can also assist in the regeneration of a damaged peripheral nerve. If a
peripheral nerve is damaged, it may regenerate if its soma is undamaged and the neurilemma (the
plasma membrane of the schwann cell) enveloping it is intact.
12
Satellite cells are found surrounding neural somas in peripheral ganglia (collections of cell bodies
located outside the CNS). Satellite cells resemble CNS astrocytes and are thought to have similar
functions, providing structural support and regulating the chemical environment.
Axons: white and Grey matter
Neuronal axons in the CNS and PNS can be devoid of a glial cell wrap (unmyelinated) or they can
be discontinuously wrapped by glial cells along their entire length (myelinated). In a myelinated
axon, the bare regions where the sheath is interrupted are called Nodes of Ranvier. The myelinated
segments between consecutive nodes of Ranvier are called internodes. The myelin sheath changes
the appearance of axons as well as their electrical properties. Myelinated axons appear white when
viewed by the naked eye in contrast to areas where neuronal cell bodies are concentrated which
appear gray.
1.3 NEUROPHYSIOLOGY
Neurons produce electrical signals as a way of conveying information from one place in the body to
another place very quickly, at speeds up to 100 meters/second (200 miles per hour). These rapidly
travelling electrical signals allow you to perceive sensory stimuli, like the sound of a passing fire
truck blasting its siren. Electrical signals, travelling in different neural pathways, coordinate motor
responses that allow you to move your car out of the way of the fire truck, withdraw your hand from
a dangerously hot pan, and rhythmically contract your diaphragm to breathe. Electrical signals arise
as a result of movement of ions back and forth across the cell membrane of neurons. As ions move
down their electrochemical gradients, they carry their charge with them, creating very miniscule but
physiologically important electrical currents. These ionic currents flowing across membranes are
the basis for the propagating electrical signals that underlie all nervous system functions.
A. Cell membrane voltage
All living, eukaryotic cells have a transmembrane potential (a difference in charges between the
intracellular and extracellular fluid). While the cell is at rest (i.e. unstimulated), the transmembrane
potential is stable and is called the resting membrane potential (RMP). Right at the cell membrane,
there is a little excess negative charge on the inside of the cell membrane and a little excess of
positive charge on the outside. Because separation of charges creates a voltage, a very small probe
on a voltmeter can be used to measure the voltage across the cell membrane. By convention the
voltage outside the cell is set to zero. In a typical cell, the voltage recorded across the membrane is
between – 60 and -90 millivolts (-.06 to -.09 volts) with the negative sign indicating that the inside of
the cell is negative with respect to the outside. Some cells have the ability to transiently alter their
transmembrane potential (excitable cells), while others do not (non-excitable cells).
Non-excitable cells (eg. intestinal epithelial cells) have a stable and unchanging RMP. Excitable
cells, like neurons and muscle, have a membrane potential that can fluctuate under certain conditions,
with each fluctuation representing a signal produced by the cell. These fluctuations may be small and
local to a region of a cell membrane (often called local or graded potentials) or larger in magnitude
Satellite cells are found surrounding neural somas in peripheral ganglia (collections of cell bodies
located outside the CNS). Satellite cells resemble CNS astrocytes and are thought to have similar
functions, providing structural support and regulating the chemical environment.
Axons: white and Grey matter
Neuronal axons in the CNS and PNS can be devoid of a glial cell wrap (unmyelinated) or they can
be discontinuously wrapped by glial cells along their entire length (myelinated). In a myelinated
axon, the bare regions where the sheath is interrupted are called Nodes of Ranvier. The myelinated
segments between consecutive nodes of Ranvier are called internodes. The myelin sheath changes
the appearance of axons as well as their electrical properties. Myelinated axons appear white when
viewed by the naked eye in contrast to areas where neuronal cell bodies are concentrated which
appear gray.
1.3 NEUROPHYSIOLOGY
Neurons produce electrical signals as a way of conveying information from one place in the body to
another place very quickly, at speeds up to 100 meters/second (200 miles per hour). These rapidly
travelling electrical signals allow you to perceive sensory stimuli, like the sound of a passing fire
truck blasting its siren. Electrical signals, travelling in different neural pathways, coordinate motor
responses that allow you to move your car out of the way of the fire truck, withdraw your hand from
a dangerously hot pan, and rhythmically contract your diaphragm to breathe. Electrical signals arise
as a result of movement of ions back and forth across the cell membrane of neurons. As ions move
down their electrochemical gradients, they carry their charge with them, creating very miniscule but
physiologically important electrical currents. These ionic currents flowing across membranes are
the basis for the propagating electrical signals that underlie all nervous system functions.
A. Cell membrane voltage
All living, eukaryotic cells have a transmembrane potential (a difference in charges between the
intracellular and extracellular fluid). While the cell is at rest (i.e. unstimulated), the transmembrane
potential is stable and is called the resting membrane potential (RMP). Right at the cell membrane,
there is a little excess negative charge on the inside of the cell membrane and a little excess of
positive charge on the outside. Because separation of charges creates a voltage, a very small probe
on a voltmeter can be used to measure the voltage across the cell membrane. By convention the
voltage outside the cell is set to zero. In a typical cell, the voltage recorded across the membrane is
between – 60 and -90 millivolts (-.06 to -.09 volts) with the negative sign indicating that the inside of
the cell is negative with respect to the outside. Some cells have the ability to transiently alter their
transmembrane potential (excitable cells), while others do not (non-excitable cells).
Non-excitable cells (eg. intestinal epithelial cells) have a stable and unchanging RMP. Excitable
cells, like neurons and muscle, have a membrane potential that can fluctuate under certain conditions,
with each fluctuation representing a signal produced by the cell. These fluctuations may be small and
local to a region of a cell membrane (often called local or graded potentials) or larger in magnitude
and travel along the length of the cell. These latter potentials, called action potentials, always lead to
some response by the cells. In a neuron, action potentials lead to neurotransmitter release.
B. Neuron resting membrane potential
Ionic composition of the ECF versus the ICF
Ions are not evenly distributed between the inside and the outside of a cell. Sodium is nearly 10
times more concentrated outside the cell than inside. Conversely, potassium is nearly 30 times
more concentrated inside the cell than outside. The uneven distribution of ion leads to concentration
gradients across the cell membrane. Given the opportunity, ions will move down their concentration
gradient (i.e from an area where they are highly concentrated to an area where they are less
concentrated). So, given the chance, sodium ions would move into the cell and potassium ions
would move out of the cell based on their respective concentration gradients.
However, the cell membrane is not freely permeable to ions. Ions cannot freely cross the plasma
membrane because of its structure. The lipid core of the cell membrane is hydrophobic and does
not allow charged molecules to pass through it. Rather the cell membrane is selectively permeable,
meaning it allows certain ions to pass. You know that the ions do not pass directly through the cell
membrane, but rather pass through ion channels. The membrane is permeable to a specific ion if
there are open channels for that ion. Recall that ion channels open and close based on the presence
of electrical or chemical stimuli. Voltage-gated channels open at specific membrane potentials and
are either inactivated (while the stimulus persists) or close when the membrane potential changes.
Ligand-gated channels open when they bind chemicals and close when the chemical is no longer
bound.
At rest, the cell membrane is most permeable to potassium because there are more open potassium
channels at the resting membrane potential than channels for any other ion. As a result, potassium
“leaks” out of the resting cell. The resting membrane is less permeable to sodium, and at rest, a
small amount of sodium “leaks” into the cell.
If these were the only things happening in the resting cell, the resting membrane potential would not
be stable, but rather the net movement of potassium ions would cause the membrane potential to
change. Ions move not only based on their individual concentration gradients, but they also move
based on charge attraction and repulsion. Ions move away from like charges (eg. sodium and
potassium ions move away from each other) and move towards opposite charges (eg. potassium
ions would move toward chloride ions). The net movement of a particular ion is influenced by its
Ion Extracellular fluid (mM) Intracellular fluid (mM)
K
+
5 150
Na
+
145 15
Cl
-
108 10
Ca
2+
1 0.0001
some response by the cells. In a neuron, action potentials lead to neurotransmitter release.
B. Neuron resting membrane potential
Ionic composition of the ECF versus the ICF
Ions are not evenly distributed between the inside and the outside of a cell. Sodium is nearly 10
times more concentrated outside the cell than inside. Conversely, potassium is nearly 30 times
more concentrated inside the cell than outside. The uneven distribution of ion leads to concentration
gradients across the cell membrane. Given the opportunity, ions will move down their concentration
gradient (i.e from an area where they are highly concentrated to an area where they are less
concentrated). So, given the chance, sodium ions would move into the cell and potassium ions
would move out of the cell based on their respective concentration gradients.
However, the cell membrane is not freely permeable to ions. Ions cannot freely cross the plasma
membrane because of its structure. The lipid core of the cell membrane is hydrophobic and does
not allow charged molecules to pass through it. Rather the cell membrane is selectively permeable,
meaning it allows certain ions to pass. You know that the ions do not pass directly through the cell
membrane, but rather pass through ion channels. The membrane is permeable to a specific ion if
there are open channels for that ion. Recall that ion channels open and close based on the presence
of electrical or chemical stimuli. Voltage-gated channels open at specific membrane potentials and
are either inactivated (while the stimulus persists) or close when the membrane potential changes.
Ligand-gated channels open when they bind chemicals and close when the chemical is no longer
bound.
At rest, the cell membrane is most permeable to potassium because there are more open potassium
channels at the resting membrane potential than channels for any other ion. As a result, potassium
“leaks” out of the resting cell. The resting membrane is less permeable to sodium, and at rest, a
small amount of sodium “leaks” into the cell.
If these were the only things happening in the resting cell, the resting membrane potential would not
be stable, but rather the net movement of potassium ions would cause the membrane potential to
change. Ions move not only based on their individual concentration gradients, but they also move
based on charge attraction and repulsion. Ions move away from like charges (eg. sodium and
potassium ions move away from each other) and move towards opposite charges (eg. potassium
ions would move toward chloride ions). The net movement of a particular ion is influenced by its
Ion Extracellular fluid (mM) Intracellular fluid (mM)
K
+
5 150
Na
+
145 15
Cl
-
108 10
Ca
2+
1 0.0001
14
electrochemical gradient (the balance of its concentration gradient and any charge attraction or
repulsion).
One final factor also plays a role in determining the RMP. The sodium potassium pump operates
continually in living cells. At maximum capacity, it pumps 3 sodium ions out of the cell and 2 potassium
ions into the cell, and hydrolyzes 1 ATP to provide the energy for the ion transport.
Sodium
Extracellular space
Potassium
K
+Na
+
ATP
ADP P
i
Intracellular space
Concentration
+–
Na
+
+–
K
+
The sodium potassium pump transports 3 Na to the ECF and 2 K to the ICF
+ +
Cell membrane
The sodium potassium pump is electrogenic (there are an uneven number of charges transported
into and out of the cell resulting in a net charge associated with each exchange cycle). Since 3
sodium ions leave the cell and only 2 potassium ions enter the cell, there is a net negative charge on
the inside of the cell due to the sodium potassium pump.
C. Neuron electrical response
This ion movement produces a change in the membrane voltage around the area of the open channels.
These local shifts in membrane potential are called local (or graded) potentials. Local potentials have
the following characteristics.
They are graded, which means the change in membrane voltage that occurs is proportional to the
size of the stimulus. A stronger stimulus can open more ion channels. A stimulus that lasts for a long
time can either open more ion channels or keep channels open for a longer time. In either case, more
ions are able to cross the cell membrane, which produces a larger change in membrane voltage.
They are decremental, meaning that the signal grows weaker as it moves farther from the site of
stimulation. Ion channels are opened at the site of stimulation and that is where ions move across the
cell membrane. As a result, there is a high concentration of ions right around the ion channels. Once the
ions cross the membrane, they diffuse away from the channel and there are fewer and fewer ions as
they move away from the open channels. Fewer ions results in a smaller change in membrane potential.
They are reversible. If the stimulus comes to an end, the ion channels close and resting membrane
potential is re- established before the signal travels very far.
electrochemical gradient (the balance of its concentration gradient and any charge attraction or
repulsion).
One final factor also plays a role in determining the RMP. The sodium potassium pump operates
continually in living cells. At maximum capacity, it pumps 3 sodium ions out of the cell and 2 potassium
ions into the cell, and hydrolyzes 1 ATP to provide the energy for the ion transport.
Sodium
Extracellular space
Potassium
K
+Na
+
ATP
ADP P
i
Intracellular space
Concentration
+–
Na
+
+–
K
+
The sodium potassium pump transports 3 Na to the ECF and 2 K to the ICF
+ +
Cell membrane
The sodium potassium pump is electrogenic (there are an uneven number of charges transported
into and out of the cell resulting in a net charge associated with each exchange cycle). Since 3
sodium ions leave the cell and only 2 potassium ions enter the cell, there is a net negative charge on
the inside of the cell due to the sodium potassium pump.
C. Neuron electrical response
This ion movement produces a change in the membrane voltage around the area of the open channels.
These local shifts in membrane potential are called local (or graded) potentials. Local potentials have
the following characteristics.
They are graded, which means the change in membrane voltage that occurs is proportional to the
size of the stimulus. A stronger stimulus can open more ion channels. A stimulus that lasts for a long
time can either open more ion channels or keep channels open for a longer time. In either case, more
ions are able to cross the cell membrane, which produces a larger change in membrane voltage.
They are decremental, meaning that the signal grows weaker as it moves farther from the site of
stimulation. Ion channels are opened at the site of stimulation and that is where ions move across the
cell membrane. As a result, there is a high concentration of ions right around the ion channels. Once the
ions cross the membrane, they diffuse away from the channel and there are fewer and fewer ions as
they move away from the open channels. Fewer ions results in a smaller change in membrane potential.
They are reversible. If the stimulus comes to an end, the ion channels close and resting membrane
potential is re- established before the signal travels very far.
15
They can either excite the cell or inhibit the cell depending on what type of ion channel is opened.
If the stimulus opens a sodium channel, sodium ions enter the cell and deporlarizes (make the
memebrane potential less negative) the membrane around the open channels. If the stimulus opens
a chloride channel, chloride ions enter the cell and make the local membrane potential more negative
than the RMP (hyperpolarizes the cell). Depolarization excites the cell and makes it more likely to
send a signal to other cells. Hyperpolarization inhibits the cell and makes it less likely to send a
signal to other cells.
A stimulus can also affect potassium channels. If the stimulus causes potassium channels to open,
the effect will be hyperpolarization of that area of cell membrane. Potassium leaves the cell through
the open channels, which removes positive charges from the ICF making the inside of the cell more
negative. If the stimulus closes potassium channels, the membrane will depolarize around the closed
channels because fewer potassium ions are leaving the cell.
Neurons generally receive multiple stimuli at the same time – some may be excitatory and others
inhibitory. The overall response of the neuron will depend on the net effect of all the stimuli. In some
cases, the neuron will produce a signal that will travel to other cells. In other cases, no signal will be
sent from the neuron.
D. Action potentials
If there is adequate excitatory stimulation of a neuron, a signal called an action potential is generated.
An action potential is a transient and marked shift in membrane potential that occurs when voltage-
gated ion channels in the membrane open. A series of action potentials can rapidly carry information
from the neural soma along the axon to the axon terminal. A sufficient number of voltage-gated
channels must be present in the cell membrane to initiate an action potential. The dendrites and
most of the soma lack enough voltage gated ion channels for this. However, at the trigger zone ,
where the soma interfaces with the axon, there is a high concentration of voltage-gated channels.
To create an action potential in a neuron, an excitatory local potential must reach the trigger zone
and depolarize (a shift in membrane potential making it less negative or even positive) it to the
threshold voltage needed to open the ion channels.
Two types of voltage-gated channel are responsible for the propagating action potentials in most
neurons- a fast Na
+
channel (a voltage gated Na
+
channel that opens quickly when stimulated) and
a slow K
+
channel (a voltage gated K
+
channel that opens slowly when stimulated). Let’s take a
closer look at the specific events of an action potential.
Excitatory local potentials reach the trigger zone and depolarize it. If the local potentials depolarize
the membrane to threshold (the membrane voltage at which the voltage gated channels are stimulated
to open), these voltage gated channels begin to open. The fast Na
+
channel opens quickly, increasing
the permeability of the membrane to Na
+
that flows into the cell down its electrochemical gradient
leading to further depolarization. This causes more fast Na
+
channels to open, further depolarizing
the membrane. As the membrane potential reaches 0 mV, the fast Na
+
channels become “inactivated”.
A second gate that works like a timer closes the channel. By the time all the fast Na
+
channels are
inactivated the membrane voltage has reached its peak.
They can either excite the cell or inhibit the cell depending on what type of ion channel is opened.
If the stimulus opens a sodium channel, sodium ions enter the cell and deporlarizes (make the
memebrane potential less negative) the membrane around the open channels. If the stimulus opens
a chloride channel, chloride ions enter the cell and make the local membrane potential more negative
than the RMP (hyperpolarizes the cell). Depolarization excites the cell and makes it more likely to
send a signal to other cells. Hyperpolarization inhibits the cell and makes it less likely to send a
signal to other cells.
A stimulus can also affect potassium channels. If the stimulus causes potassium channels to open,
the effect will be hyperpolarization of that area of cell membrane. Potassium leaves the cell through
the open channels, which removes positive charges from the ICF making the inside of the cell more
negative. If the stimulus closes potassium channels, the membrane will depolarize around the closed
channels because fewer potassium ions are leaving the cell.
Neurons generally receive multiple stimuli at the same time – some may be excitatory and others
inhibitory. The overall response of the neuron will depend on the net effect of all the stimuli. In some
cases, the neuron will produce a signal that will travel to other cells. In other cases, no signal will be
sent from the neuron.
D. Action potentials
If there is adequate excitatory stimulation of a neuron, a signal called an action potential is generated.
An action potential is a transient and marked shift in membrane potential that occurs when voltage-
gated ion channels in the membrane open. A series of action potentials can rapidly carry information
from the neural soma along the axon to the axon terminal. A sufficient number of voltage-gated
channels must be present in the cell membrane to initiate an action potential. The dendrites and
most of the soma lack enough voltage gated ion channels for this. However, at the trigger zone ,
where the soma interfaces with the axon, there is a high concentration of voltage-gated channels.
To create an action potential in a neuron, an excitatory local potential must reach the trigger zone
and depolarize (a shift in membrane potential making it less negative or even positive) it to the
threshold voltage needed to open the ion channels.
Two types of voltage-gated channel are responsible for the propagating action potentials in most
neurons- a fast Na
+
channel (a voltage gated Na
+
channel that opens quickly when stimulated) and
a slow K
+
channel (a voltage gated K
+
channel that opens slowly when stimulated). Let’s take a
closer look at the specific events of an action potential.
Excitatory local potentials reach the trigger zone and depolarize it. If the local potentials depolarize
the membrane to threshold (the membrane voltage at which the voltage gated channels are stimulated
to open), these voltage gated channels begin to open. The fast Na
+
channel opens quickly, increasing
the permeability of the membrane to Na
+
that flows into the cell down its electrochemical gradient
leading to further depolarization. This causes more fast Na
+
channels to open, further depolarizing
the membrane. As the membrane potential reaches 0 mV, the fast Na
+
channels become “inactivated”.
A second gate that works like a timer closes the channel. By the time all the fast Na
+
channels are
inactivated the membrane voltage has reached its peak.
16
As the fast Na
+
channels are being inactivated, the slow K
+
channels are finally opening. This increases
the permeability of the membrane to K
+
. Potassium ions leave the cell moving down their
electrochemical gradient, and the efflux of positive charge causes the membrane voltage to return
toward the resting membrane potential (repolarization).
Slow K
+
channels stay open longer than fast Na
+
channels, so more K
+
leaves the cell than Na
+
entered. The removal of excess potassium ions causes the membrane potential to become more
negative than the resting membrane potential. When this happens, we say the membrane is
hyperpolarized.
Na gates start
opening and some
Na enter into the
axon (K gates are closed)
+
+
+
NEURON INTERIOR
Resting potential;
maintainted by
pump, and permeable
for ions by diffusion
Na -K
K
+ +
+
Na
K
K
+
+
+
gates closed:
gates open, and
more outflux or
Efflux
Many Na
K gates are closed)
+
+
+
Action potential
gates open
and more Na influx. (
Overshoot
+ + + + + + + +
+ + + + + + + +
2 Na
+
+ + + + + + + +
+ + + + + + + +
1
K
+
+ + + + + + + +
+ + + + + + + +
K
+
Na
+
+ + + + +
++
+ + + + +
++
Na
+
+ 50
+ 40
+ 30
+ 20
0
- 20
- 40
- 60
- 70
- 80
0 1 2 3 4 5 6 7
Milli seconds
Hyperpolarisation
{Threshold
level
Depolarisation
Repolarisation
4
3
M
e
m
b
r
a
n
e
p
o
t
e
n
t
ia
l
(
m
v
)
E. Action potential refractory period
The duration of time that the membrane is hyperpolarized following an action potential is termed its
refractory period. The refractory period is an interval of time during which that part of the membrane
cannot be excited ( to produce another action potential) or requires a larger than normal stimulus to
be excited. The refractory period is divided into two parts based on whether or not the membrane
can be stimulated to produce an action potential. During the absolute refractory period, the
membrane cannot be stimulated to produce another action potential regardless of the strength of
the stimulus. During the relative refractory period, the membrane can be stimulated to produce
an action potential, but a stronger than normal stimulus is required.
As the fast Na
+
channels are being inactivated, the slow K
+
channels are finally opening. This increases
the permeability of the membrane to K
+
. Potassium ions leave the cell moving down their
electrochemical gradient, and the efflux of positive charge causes the membrane voltage to return
toward the resting membrane potential (repolarization).
Slow K
+
channels stay open longer than fast Na
+
channels, so more K
+
leaves the cell than Na
+
entered. The removal of excess potassium ions causes the membrane potential to become more
negative than the resting membrane potential. When this happens, we say the membrane is
hyperpolarized.
Na gates start
opening and some
Na enter into the
axon (K gates are closed)
+
+
+
NEURON INTERIOR
Resting potential;
maintainted by
pump, and permeable
for ions by diffusion
Na -K
K
+ +
+
Na
K
K
+
+
+
gates closed:
gates open, and
more outflux or
Efflux
Many Na
K gates are closed)
+
+
+
Action potential
gates open
and more Na influx. (
Overshoot
+ + + + + + + +
+ + + + + + + +
2 Na
+
+ + + + + + + +
+ + + + + + + +
1
K
+
+ + + + + + + +
+ + + + + + + +
K
+
Na
+
+ + + + +
++
+ + + + +
++
Na
+
+ 50
+ 40
+ 30
+ 20
0
- 20
- 40
- 60
- 70
- 80
0 1 2 3 4 5 6 7
Milli seconds
Hyperpolarisation
{Threshold
level
Depolarisation
Repolarisation
4
3
M
e
m
b
r
a
n
e
p
o
t
e
n
t
ia
l
(
m
v
)
E. Action potential refractory period
The duration of time that the membrane is hyperpolarized following an action potential is termed its
refractory period. The refractory period is an interval of time during which that part of the membrane
cannot be excited ( to produce another action potential) or requires a larger than normal stimulus to
be excited. The refractory period is divided into two parts based on whether or not the membrane
can be stimulated to produce an action potential. During the absolute refractory period, the
membrane cannot be stimulated to produce another action potential regardless of the strength of
the stimulus. During the relative refractory period, the membrane can be stimulated to produce
an action potential, but a stronger than normal stimulus is required.
17
The absolute refractory period lasts from the beginning of the action potential (when the membrane
reaches the threshold voltage) until the fast Na
+
channels reset to their resting state. As long as the
Na
+
channels are open or inactivated, a new action potential cannot be generated.
The relative refractory period continues from the end of the absolute refractory period until the
membrane is no longer hyperpolarized (returns to the resting membrane potential). During
hyperpolarization, slow K
+
channels are still open, but are in the process of closing. In order to
stimulate an action potential during this time, a very strong stimulus is needed to overcome the
effect of potassium flowing out of the cell and depolarize the cell.
Previously, we considered the characteristics of local potentials. They are graded, decremental,
reversible, and can either excite or inhibit the membrane. In contrast, action potentials are all or
none, nondecremental, irreversible and always excitatory.
Action potentials within a particular cell are all identical regardless of stimulus strength. If the
membrane at the trigger zone reaches the threshold voltage or a voltage above the threshold, a
maximal action potential will be generated. If the threshold voltage is not attained, no action potential
is generated (no signal is propagated). In this way, action potentials are all-or-none-a cell either fires
a full action potentials or no action potential at all.
The action potential at the axon terminal looks exactly like the action potential that was initially
generated at the trigger zone. Since the signal does not change as it travels the length of the axon
it is non-decremental. It should be noted that the action potential at the axon terminal is not the
same one that originated at the trigger zone, Rather, a series of identical action potentials are
generated as the signal travels toward the axon terminal.
If the membrane reaches threshold, an action potential will be initiated and the signal will be
propagated down the entire axon. Once the events are set in motion there is no stopping them. The
process is irreversible.
In contrast to local potentials, which can either excite or inhibit the membrane, action potentials are
all excitatory (cause an initial depolarization of the membrane).
F. Synapses
A synapse is the structure that allows a neuron to pass an electrical or chemical signal to another
cell.
The cell that delivers the signal to the synapse is the presynaptic cell. The cell that will receive the
signal once it crosses the synapse is the postsynaptic cell. Since most neural pathways contain
several neurons, a postsynaptic neuron at one synapse may become the presynaptic neuron for
another cell downstream.
A presynaptic neuron can form one of three types of synapses with a postsynaptic neuron. The most
common type of synapse is an axodendritic synapse, where the axon of the presynaptic neuron
synapses with a dendrite of the postsynaptic neuron. If the presynaptic neuron synapses with the
soma of the postsynaptic neuron it is called an axosomatic synapse, and if it synapses with the axon
The absolute refractory period lasts from the beginning of the action potential (when the membrane
reaches the threshold voltage) until the fast Na
+
channels reset to their resting state. As long as the
Na
+
channels are open or inactivated, a new action potential cannot be generated.
The relative refractory period continues from the end of the absolute refractory period until the
membrane is no longer hyperpolarized (returns to the resting membrane potential). During
hyperpolarization, slow K
+
channels are still open, but are in the process of closing. In order to
stimulate an action potential during this time, a very strong stimulus is needed to overcome the
effect of potassium flowing out of the cell and depolarize the cell.
Previously, we considered the characteristics of local potentials. They are graded, decremental,
reversible, and can either excite or inhibit the membrane. In contrast, action potentials are all or
none, nondecremental, irreversible and always excitatory.
Action potentials within a particular cell are all identical regardless of stimulus strength. If the
membrane at the trigger zone reaches the threshold voltage or a voltage above the threshold, a
maximal action potential will be generated. If the threshold voltage is not attained, no action potential
is generated (no signal is propagated). In this way, action potentials are all-or-none-a cell either fires
a full action potentials or no action potential at all.
The action potential at the axon terminal looks exactly like the action potential that was initially
generated at the trigger zone. Since the signal does not change as it travels the length of the axon
it is non-decremental. It should be noted that the action potential at the axon terminal is not the
same one that originated at the trigger zone, Rather, a series of identical action potentials are
generated as the signal travels toward the axon terminal.
If the membrane reaches threshold, an action potential will be initiated and the signal will be
propagated down the entire axon. Once the events are set in motion there is no stopping them. The
process is irreversible.
In contrast to local potentials, which can either excite or inhibit the membrane, action potentials are
all excitatory (cause an initial depolarization of the membrane).
F. Synapses
A synapse is the structure that allows a neuron to pass an electrical or chemical signal to another
cell.
The cell that delivers the signal to the synapse is the presynaptic cell. The cell that will receive the
signal once it crosses the synapse is the postsynaptic cell. Since most neural pathways contain
several neurons, a postsynaptic neuron at one synapse may become the presynaptic neuron for
another cell downstream.
A presynaptic neuron can form one of three types of synapses with a postsynaptic neuron. The most
common type of synapse is an axodendritic synapse, where the axon of the presynaptic neuron
synapses with a dendrite of the postsynaptic neuron. If the presynaptic neuron synapses with the
soma of the postsynaptic neuron it is called an axosomatic synapse, and if it synapses with the axon
18
of the postsynaptic cell it is an axoaxonic synapse. Although our illustration shows a single synapse,
neurons typically have many (even 10,000 or more) synapses.
There are two types of synapses found in your body: electrical and chemical. Electrical synapses
allow the direct passage of ions and signaling molecules from cell to cell. In contrast, chemical
synapses do not pass the signal directly from the presynaptic cell to the postsynaptic cell. In a
chemical synapse, an action potential in the presynaptic neuron leads to the release of a chemical
messenger called a neurotransmitter. The neurotransmitter then diffuses across the synapse and
binds to receptors on the postsynaptic cell. Binding of the neurotransmitter leads to the production
of an electrical signal in the postsynaptic cell.
Why does the body have two types of synapses? Each type of synapse has functional advantages
and disadvantages. An electrical synapse passes the signal very quickly, which allows groups of
cells to act in unison. A chemical synapse takes much longer to transmit the signal from one cell to
the next; however, chemical synapses allow neurons to integrate information from multiple presynaptic
neurons, determining whether or not the postsynaptic cell will continue to propagate the signal.
Neurons respond differently based on information transmitted by multiple chemical synapses.
Electrical synapses transmit action potentials via the direct flow of electrical current at Gap
junctions. Gap junctions are formed when two adjacent cells have transmembrane pores that
align. The membranes of the two cells are linked together and the aligned pores form a passage
between the cells. Consequently, several types of molecules and ions are allowed to pass between
the cells. Due to the direct flow of ions and molecules from one cell to another, electrical synapses
allow bidirectional flow of information between cells. Gap junctions are crucial to the functioning of
the cardiac myocytes and smooth muscles.
Closed Open
Connexon
Connexin monomer
Plasma membranes
Intercellular space
2-4 nm space
Hydrophilic channel
Structure of an electrical synapse (gap junction)
Chemical synapses comprise most of the synapses in your body. In a chemical synapse, a synaptic
gap or cleft separates the pre- and the postsynaptic cells. An action potential propagated to the
axon terminal results in the secretion of chemical messengers, called neurotransmitters, from the
of the postsynaptic cell it is an axoaxonic synapse. Although our illustration shows a single synapse,
neurons typically have many (even 10,000 or more) synapses.
There are two types of synapses found in your body: electrical and chemical. Electrical synapses
allow the direct passage of ions and signaling molecules from cell to cell. In contrast, chemical
synapses do not pass the signal directly from the presynaptic cell to the postsynaptic cell. In a
chemical synapse, an action potential in the presynaptic neuron leads to the release of a chemical
messenger called a neurotransmitter. The neurotransmitter then diffuses across the synapse and
binds to receptors on the postsynaptic cell. Binding of the neurotransmitter leads to the production
of an electrical signal in the postsynaptic cell.
Why does the body have two types of synapses? Each type of synapse has functional advantages
and disadvantages. An electrical synapse passes the signal very quickly, which allows groups of
cells to act in unison. A chemical synapse takes much longer to transmit the signal from one cell to
the next; however, chemical synapses allow neurons to integrate information from multiple presynaptic
neurons, determining whether or not the postsynaptic cell will continue to propagate the signal.
Neurons respond differently based on information transmitted by multiple chemical synapses.
Electrical synapses transmit action potentials via the direct flow of electrical current at Gap
junctions. Gap junctions are formed when two adjacent cells have transmembrane pores that
align. The membranes of the two cells are linked together and the aligned pores form a passage
between the cells. Consequently, several types of molecules and ions are allowed to pass between
the cells. Due to the direct flow of ions and molecules from one cell to another, electrical synapses
allow bidirectional flow of information between cells. Gap junctions are crucial to the functioning of
the cardiac myocytes and smooth muscles.
Closed Open
Connexon
Connexin monomer
Plasma membranes
Intercellular space
2-4 nm space
Hydrophilic channel
Structure of an electrical synapse (gap junction)
Chemical synapses comprise most of the synapses in your body. In a chemical synapse, a synaptic
gap or cleft separates the pre- and the postsynaptic cells. An action potential propagated to the
axon terminal results in the secretion of chemical messengers, called neurotransmitters, from the
19
axon terminals. The neurotransmitter molecules diffuse across the synaptic cleft and bind to receptor
on the cell membrane of the postsynaptic cell. Binding of neurotransmitter ot the receptor proteins
on the postsynaptic cell leads to a transient change in the postsynaptic cells membrane potential.
Microtubule
Cytoplasm
Mitochondrion
Presynaptic
neuron Synaptic vesicle
Presynaptic neuron
Ions flow through
gap junction channels
Neurotransmitter released
Gap
junction
Postsynaptic
neuron
Postsynaptic
neuron
Presynaptic
membrane
Synaptic
vesicle fusing Presynaptic membrane
Postsynaptic membrane
Gap junction channels
Synaptic
cleft
Postsynaptic neurotransmitter
receptor
Ions flow through
postsynaptic
channels
Postsynaptic
membrane
Structure of a chemical synapse
The process of synaptic transmission at a chemical synapse between two neurons follows these steps:
An action potential, propagating along the axon of a presynaptic neuron, arrives at the axon
terminal.
The depolarization of the axolemma (the plasma membrane of the axon) at the axon terminal
opens Ca
2+
channels and Ca
2+
diffuses into the axon terminal.
Ca
2+
bind with calmodulin, the ubiquitous intracellular calcium receptor, causing the synaptic
vesicles to migrate and to fuse with the presynaptic membrane.
The neurotransmitter is released into the synaptic cleft by the process of exocytosis.
The neurotransmitter diffuses across the synaptic cleft and binds with receptors on the
postsynaptic membrane.
Binding of the neurotransmitters to the postsynaptic receptors causes a response in the
postsynaptic cell,
The response can be of two kinds:
axon terminals. The neurotransmitter molecules diffuse across the synaptic cleft and bind to receptor
on the cell membrane of the postsynaptic cell. Binding of neurotransmitter ot the receptor proteins
on the postsynaptic cell leads to a transient change in the postsynaptic cells membrane potential.
Microtubule
Cytoplasm
Mitochondrion
Presynaptic
neuron Synaptic vesicle
Presynaptic neuron
Ions flow through
gap junction channels
Neurotransmitter released
Gap
junction
Postsynaptic
neuron
Postsynaptic
neuron
Presynaptic
membrane
Synaptic
vesicle fusing Presynaptic membrane
Postsynaptic membrane
Gap junction channels
Synaptic
cleft
Postsynaptic neurotransmitter
receptor
Ions flow through
postsynaptic
channels
Postsynaptic
membrane
Structure of a chemical synapse
The process of synaptic transmission at a chemical synapse between two neurons follows these steps:
An action potential, propagating along the axon of a presynaptic neuron, arrives at the axon
terminal.
The depolarization of the axolemma (the plasma membrane of the axon) at the axon terminal
opens Ca
2+
channels and Ca
2+
diffuses into the axon terminal.
Ca
2+
bind with calmodulin, the ubiquitous intracellular calcium receptor, causing the synaptic
vesicles to migrate and to fuse with the presynaptic membrane.
The neurotransmitter is released into the synaptic cleft by the process of exocytosis.
The neurotransmitter diffuses across the synaptic cleft and binds with receptors on the
postsynaptic membrane.
Binding of the neurotransmitters to the postsynaptic receptors causes a response in the
postsynaptic cell,
The response can be of two kinds:
20
1. A neurotransmitter may bind to a receptor that is associated with a specific ion channel
which, when opened, allows for diffusion of an ion through the channel. If Na
+
channels
are opened, Na
+
rapidly diffuses into the postsynaptic cell and depolarizes the membrane
towards the threshold for an action potential. If K
+
channels are opened, K
+
diffuses out of
the cell, depressing the membrane polarity below its resting potential (hyperpolarization).
If Cl
-
channels are opened, Cl
-
moves into the cell leading to hyperpolarization.
2. The neurotransmitter may bind to a transmembrane receptor protein, causing it to activate
a G protein on the inside surface of the postsynaptic membrane. A cascade of events
leads to the appearance of a second messenger (calcium ion, cyclic AMP (cAMP), or IP
3
)
in the cell. Second messengers can have diverse effect on the cell ranging from opening
an ion channel to changing cell metabolism to initiating transcription of new proteins.
TARGET POINTS
When the AP develops in presynaptic membrane. It becomes permeable for Ca
++
. Ca
++
enters
in and vesicles burst due to the stimulation and release neurotransmitters (Ach) in synaptic
cleft. Ach reaches the post synaptic membrane via synaptic cleft and bind to receptors. It
develops excitatory post synaptic potential (EPSP). EPSP develop due to opening of Na
+
gated channels. Cholinesterase enzyme is found in the postsynaptic membrane. This enzyme
decomposes the Ach into choline and acetate.
Neuro-inhibitory transmitter (GABA) binds with postsynaptic membrane to open the Cl
-
gated
channels and hyperpolarization of neuron occurs. Now the potential is called inhibitory post
synaptic potential (IPSP) and further nerve conduction is blocked.
In human brain more than 100 billion neurons are present.
Each neuron connects with 25,000 other cells.
Glycine is neuro-inhibitory hormone present in spinal cord.
Glutamate is an excitatory amino acid.
Physiological properties of nerve fibers are detected by cathode ray oscilloscope.
Stimulates impulse at synapse
Eg. acetyl choline (Ach),
nor-epinephrine or
nor-adrenaline or sympathetin
Neurotransmitters Neurohumors Neurohormonesor or
Stimulatory Inhibitory
Inhibit impulse at synapse Eg. GABA (Gamma Amino
Butyric Acid), dopamine, glycine
1. A neurotransmitter may bind to a receptor that is associated with a specific ion channel
which, when opened, allows for diffusion of an ion through the channel. If Na
+
channels
are opened, Na
+
rapidly diffuses into the postsynaptic cell and depolarizes the membrane
towards the threshold for an action potential. If K
+
channels are opened, K
+
diffuses out of
the cell, depressing the membrane polarity below its resting potential (hyperpolarization).
If Cl
-
channels are opened, Cl
-
moves into the cell leading to hyperpolarization.
2. The neurotransmitter may bind to a transmembrane receptor protein, causing it to activate
a G protein on the inside surface of the postsynaptic membrane. A cascade of events
leads to the appearance of a second messenger (calcium ion, cyclic AMP (cAMP), or IP
3
)
in the cell. Second messengers can have diverse effect on the cell ranging from opening
an ion channel to changing cell metabolism to initiating transcription of new proteins.
TARGET POINTS
When the AP develops in presynaptic membrane. It becomes permeable for Ca
++
. Ca
++
enters
in and vesicles burst due to the stimulation and release neurotransmitters (Ach) in synaptic
cleft. Ach reaches the post synaptic membrane via synaptic cleft and bind to receptors. It
develops excitatory post synaptic potential (EPSP). EPSP develop due to opening of Na
+
gated channels. Cholinesterase enzyme is found in the postsynaptic membrane. This enzyme
decomposes the Ach into choline and acetate.
Neuro-inhibitory transmitter (GABA) binds with postsynaptic membrane to open the Cl
-
gated
channels and hyperpolarization of neuron occurs. Now the potential is called inhibitory post
synaptic potential (IPSP) and further nerve conduction is blocked.
In human brain more than 100 billion neurons are present.
Each neuron connects with 25,000 other cells.
Glycine is neuro-inhibitory hormone present in spinal cord.
Glutamate is an excitatory amino acid.
Physiological properties of nerve fibers are detected by cathode ray oscilloscope.
Stimulates impulse at synapse
Eg. acetyl choline (Ach),
nor-epinephrine or
nor-adrenaline or sympathetin
Neurotransmitters Neurohumors Neurohormonesor or
Stimulatory Inhibitory
Inhibit impulse at synapse Eg. GABA (Gamma Amino
Butyric Acid), dopamine, glycine
21
The velocity of nerve impulse is 5 to 50 times faster in myelinated nerve fibers than in non
myelinated nerve-fibers.
In mammals, the speed of nerve impulse is 100 – 130 m/sec (maximum). In frog, the speed of
nerve impulse is 30 m/sec. in reptiles the speed is 15 – 35 m/sec.
Acetylcholinesterase enzyme helps in the dissociation of acetylcholine.
In the form of inhibitory neurohormones. GABA (gamma amino butyric acid) is present.
Acetylcholine is synthesized by the mitochondria.
For the conduction of nerve impulses, Na
+
is necessary.
The marking of brain waves is done through E.E.G i.e. electro encephalo gram.
Curare: A drug which blocks acetylcholine on skeletal muscles to be used by a surgeon for
keeping the muscle relaxed during operation.
The velocity of nerve impulse is 5 to 50 times faster in myelinated nerve fibers than in non
myelinated nerve-fibers.
In mammals, the speed of nerve impulse is 100 – 130 m/sec (maximum). In frog, the speed of
nerve impulse is 30 m/sec. in reptiles the speed is 15 – 35 m/sec.
Acetylcholinesterase enzyme helps in the dissociation of acetylcholine.
In the form of inhibitory neurohormones. GABA (gamma amino butyric acid) is present.
Acetylcholine is synthesized by the mitochondria.
For the conduction of nerve impulses, Na
+
is necessary.
The marking of brain waves is done through E.E.G i.e. electro encephalo gram.
Curare: A drug which blocks acetylcholine on skeletal muscles to be used by a surgeon for
keeping the muscle relaxed during operation.
22
1. A motor nerve carries impulses from
a) Cranial nerves to effectors
b) Effectors to cranial nerves
c) Effectors to central nervous system
d) Central nervous system to effectors
2. Clusters of neuron cell bodies embedded
in the white matter of the brain are referred
to as
a) Nuclei b) Gyri
c) Sulci d) Ganglia
3. Which part of nervous system is activated
under stress?
a) Autonomous nervous system
b) Parasympathetic nervous system
c) Sympathetic nervous system
d) Spinal cord
4. A nerve conveying impulses from a tissue
to nerve center is
a) Afferent b) Efferent
c) Mixed d) None of these
5. The nerves are made up exclusively from
the
a) Dendrons b) Axons
c) Nodes of Ranvier d) Nissl’s body
6. Certain kinds of stimuli produce responses
without conscious thinking. They are
a) Reflex b) Conditioning
c) Synapse d) None of these
7. Transmission of nerve impulse at synapses
is a
a) Biological process
b) Physical process
c) Chemical process
d) Mechanical process
Simple Questions
8. The functional connection between two
neurons is called
a) Synapse b) Synapsis
c) Chiasma d) Chiasmata
9. A polarized neuron is the one that is
a) Conducting stimulus
b) At resting potential
c) Having action potential
d) None of these
10. Which one does not involve brain?
a) Spinal reflex b) Cerebral reflex
c) Cranial reflex d) Voluntary reflex
11. Speed of impulse on nerves in mammals is
a) 1 m/s b) 100 m/s
c) 1000 m/s d) None of these
12. Four healthy people in their twenties got
involved in injuries resulting in damage and
death of a few cells of the following. Which
of the cells are least likely to be replaced by
new cells?
a) Osteocytes
b) Malpighian layer of the skin
c) Liver cells
d) Neurons
13. GABA (gama amino butyric acid) is a
a) Inhibitory neurohormone
b) Transmittory neurohormone
c) Anti-coagulant
d) None
14. _____ prevent the spreading of impulses
within the neighbouring fibers
a) Nodes of Ranvier
b) Synapse
c) Medullary sheaths
d) None of these
1. A motor nerve carries impulses from
a) Cranial nerves to effectors
b) Effectors to cranial nerves
c) Effectors to central nervous system
d) Central nervous system to effectors
2. Clusters of neuron cell bodies embedded
in the white matter of the brain are referred
to as
a) Nuclei b) Gyri
c) Sulci d) Ganglia
3. Which part of nervous system is activated
under stress?
a) Autonomous nervous system
b) Parasympathetic nervous system
c) Sympathetic nervous system
d) Spinal cord
4. A nerve conveying impulses from a tissue
to nerve center is
a) Afferent b) Efferent
c) Mixed d) None of these
5. The nerves are made up exclusively from
the
a) Dendrons b) Axons
c) Nodes of Ranvier d) Nissl’s body
6. Certain kinds of stimuli produce responses
without conscious thinking. They are
a) Reflex b) Conditioning
c) Synapse d) None of these
7. Transmission of nerve impulse at synapses
is a
a) Biological process
b) Physical process
c) Chemical process
d) Mechanical process
Simple Questions
8. The functional connection between two
neurons is called
a) Synapse b) Synapsis
c) Chiasma d) Chiasmata
9. A polarized neuron is the one that is
a) Conducting stimulus
b) At resting potential
c) Having action potential
d) None of these
10. Which one does not involve brain?
a) Spinal reflex b) Cerebral reflex
c) Cranial reflex d) Voluntary reflex
11. Speed of impulse on nerves in mammals is
a) 1 m/s b) 100 m/s
c) 1000 m/s d) None of these
12. Four healthy people in their twenties got
involved in injuries resulting in damage and
death of a few cells of the following. Which
of the cells are least likely to be replaced by
new cells?
a) Osteocytes
b) Malpighian layer of the skin
c) Liver cells
d) Neurons
13. GABA (gama amino butyric acid) is a
a) Inhibitory neurohormone
b) Transmittory neurohormone
c) Anti-coagulant
d) None
14. _____ prevent the spreading of impulses
within the neighbouring fibers
a) Nodes of Ranvier
b) Synapse
c) Medullary sheaths
d) None of these
23
15. Synaptic delay is the time taken between
the
a) Actual reception of a stimulus and its
perception
b) Reception of a stimulus and the resultant
sensory reaction
c) Release of a neurotransmitter from one
neuron and stimulation of the next
neuron
d) Conduction of nerve impulse across a
neuron
16. Energy transformation during nerve
conduction is chemical to
a) Radiant b) Mechanical
c) Electrical d) Osmotic
17. In a man, abducens nerve is injured. Which
one of the following functions will be
affected?
a) Movement of the eye ball
b) Swallowing
c) Movement of the tongue
d) Movement of the neck
18. Nerve impulses are inherited by nerve fibers
only when the membrane shall become
more permeable to
a) Adrenaline
b) Phosphorus
c) Sodium ions
d) Potassium ions
19. Schwann cells are present where
a) Nerve is covered with myelin sheath
b) Neurilemma and myelin sheath are
discontinuous
c) Myelin sheath is discontinuous
d) Neurilemma is discontinuous
20. Depolarization of axolemma during nerve
conduction takes place because of
a) Equal amount of Na
+
and K
+
move out
across axolemma
b) Na
+
move inside
c) More Na
+
outside
d) None
21. Axoplasm is found in
a) Out of nerve fiber
b) Inside nerve fiber
c) Around the nucleus of smooth muscle
fiber
d) Around the nucleus of neuron
22. Neurons producing hormone like
substances are
a) Neurosecretory
b) Sensory
c) Motor
d) Both (a) and (b)
23. Non-myelinated axons diff er f rom
myelinated in that they
a) Are more excitable
b) Lacks nodes of Ranvier
c) Are not capable of regeneration
d) Are not associated with schwann cells
24. Afferent nerve fibers carry impulses from
a) Effector organs to CNS
b) Receptors to CNS
c) CNS to receptors
d) CNS to muscles
25. The one way or unidirectional transmission
of nerve cells is due to
a) Synapses
b) Myelin sheath
c) Membrane polarity
d) Interneurons
15. Synaptic delay is the time taken between
the
a) Actual reception of a stimulus and its
perception
b) Reception of a stimulus and the resultant
sensory reaction
c) Release of a neurotransmitter from one
neuron and stimulation of the next
neuron
d) Conduction of nerve impulse across a
neuron
16. Energy transformation during nerve
conduction is chemical to
a) Radiant b) Mechanical
c) Electrical d) Osmotic
17. In a man, abducens nerve is injured. Which
one of the following functions will be
affected?
a) Movement of the eye ball
b) Swallowing
c) Movement of the tongue
d) Movement of the neck
18. Nerve impulses are inherited by nerve fibers
only when the membrane shall become
more permeable to
a) Adrenaline
b) Phosphorus
c) Sodium ions
d) Potassium ions
19. Schwann cells are present where
a) Nerve is covered with myelin sheath
b) Neurilemma and myelin sheath are
discontinuous
c) Myelin sheath is discontinuous
d) Neurilemma is discontinuous
20. Depolarization of axolemma during nerve
conduction takes place because of
a) Equal amount of Na
+
and K
+
move out
across axolemma
b) Na
+
move inside
c) More Na
+
outside
d) None
21. Axoplasm is found in
a) Out of nerve fiber
b) Inside nerve fiber
c) Around the nucleus of smooth muscle
fiber
d) Around the nucleus of neuron
22. Neurons producing hormone like
substances are
a) Neurosecretory
b) Sensory
c) Motor
d) Both (a) and (b)
23. Non-myelinated axons diff er f rom
myelinated in that they
a) Are more excitable
b) Lacks nodes of Ranvier
c) Are not capable of regeneration
d) Are not associated with schwann cells
24. Afferent nerve fibers carry impulses from
a) Effector organs to CNS
b) Receptors to CNS
c) CNS to receptors
d) CNS to muscles
25. The one way or unidirectional transmission
of nerve cells is due to
a) Synapses
b) Myelin sheath
c) Membrane polarity
d) Interneurons
24
26. Acetylcholinesterase enzyme splits
acetylcholine into
a) Acetone and choline
b) Acetic acid and choline
c) Amino acid and choline
d) Aspartic acid and acetylcholine
27. Action potential of a nerve cell is generated
by
a) Na
+
b) K
+
c) Ca
++
d) Cl
–
28. Resting potential of a nerve is: (in milli volt)
a) + 70 b) + 30
c) – 30 d) – 70
29. Presynaptic membrane is part of
a) Dendron b) Axon Hillock
c) Telodendria d) Soma
30. Nerve fibers are surrounded by an insulating
fatty layer called
a) Adipose sheath b) Myelin sheath
c) Hyaline sheath d) Peritoneum
31. Which one of the following does not act as
a neurotransmitter?
a) Norepinephrine
b) Cortisone
c) Acetylcholine
d) Epinephrine
32. The autonomic nerv ous system is
responsible for which function (s)?
a) Motor
b) Sensory
c) Motor and sensory
d) None of these
33. The accompanied diagram shows the
structure of neuron. Identify A to E
E
Axon
terminal
D
Myelin
sheath
Axon
C
Nucleus
B
Nissl’s
granules
A
A B C D E
a Nerve Cyton or Schwann Node of Synaptic
fibre cell body cell ranvier knob
b Dend- Cyton or Schwann Node of Synaptic
rites cell body cell ranvier knob
c Dend- Nerve Schwann Node of Synaptic
rites cell cell ranvier knob
d Dend- Cyton or Nerve Node of Synaptic
rites cell body cell ranvier knob
1. Post ganglionic sympathetic cholinergic
innervation seen in
a) Heart
b) Stomach
c) Sweat glands
d) Intestine
Difficult Questions
2. Which system relays information from CNS
a) Somatic neural system
b) Autonomic neural system
c) Peripheral neural system
d) All of these
26. Acetylcholinesterase enzyme splits
acetylcholine into
a) Acetone and choline
b) Acetic acid and choline
c) Amino acid and choline
d) Aspartic acid and acetylcholine
27. Action potential of a nerve cell is generated
by
a) Na
+
b) K
+
c) Ca
++
d) Cl
–
28. Resting potential of a nerve is: (in milli volt)
a) + 70 b) + 30
c) – 30 d) – 70
29. Presynaptic membrane is part of
a) Dendron b) Axon Hillock
c) Telodendria d) Soma
30. Nerve fibers are surrounded by an insulating
fatty layer called
a) Adipose sheath b) Myelin sheath
c) Hyaline sheath d) Peritoneum
31. Which one of the following does not act as
a neurotransmitter?
a) Norepinephrine
b) Cortisone
c) Acetylcholine
d) Epinephrine
32. The autonomic nerv ous system is
responsible for which function (s)?
a) Motor
b) Sensory
c) Motor and sensory
d) None of these
33. The accompanied diagram shows the
structure of neuron. Identify A to E
E
Axon
terminal
D
Myelin
sheath
Axon
C
Nucleus
B
Nissl’s
granules
A
A B C D E
a Nerve Cyton or Schwann Node of Synaptic
fibre cell body cell ranvier knob
b Dend- Cyton or Schwann Node of Synaptic
rites cell body cell ranvier knob
c Dend- Nerve Schwann Node of Synaptic
rites cell cell ranvier knob
d Dend- Cyton or Nerve Node of Synaptic
rites cell body cell ranvier knob
1. Post ganglionic sympathetic cholinergic
innervation seen in
a) Heart
b) Stomach
c) Sweat glands
d) Intestine
Difficult Questions
2. Which system relays information from CNS
a) Somatic neural system
b) Autonomic neural system
c) Peripheral neural system
d) All of these
25
3. Pick out the incorrect statement?
a) Myelinated nerve fibers are found in
spinal and cranial nerve
b) Unmyelinated nerve fiber is enclosed by
a schwann cells
c) In resting stage the axonal membrane
is comparatively more permeable to
potassium ion and nearly impermeable
to sodium ions
d) Axolemma is more permeable to
negatively charged protein present in the
axoplasm
4. When a neuron is in resting state i.e. not
conducting any impulse, the axonal
membrane is
a) Equally permeable to both Na
+
and K
+
ions
b) Impermeable to both Na
+
and K
+
ions
c) Comparatively more permeable to K
+
ions and nearly impermeable to Na
+
ions
d) Comparatively more permeable to Na
+
ions and nearly impermeable to K
+
ions
5. Saltatory conduction is superior to
uninterrupted conduction because of
a) Less energy required
b) More speed
c) Less Na
+
/K
+
pump
d) All of the above
6. If dorsal nerve of spinal cord is broken down
then its effect is
a) No impulse is transmitted
b) Impulse is transmitted but slowly
c) Impulse is transmitted fast
d) No effect on impulse
7. An action potential in the nerve fibers is
produced when positive and negative
charges on the outside and the inside of the
axon membrane are reversed, because
a) More K
+
enters the axon as compared
to sodium ions leaving it
b) More Na
+
enters the axon as compared
to K
+
leaving it
c) All K
+
leaving the axon
d) All Na
+
enters the axon
8. Alzheimer’s disease in humans is
associated with deficiency of
a) Dopamine
b) Glutamic acid
c) Acetylcholine
d) Gamma amino butyric acid (GABA)
9. Which of the following diagram illustrates
the distribution of Na
+
and K
+
ions in a
section of non myelinated axon which is at
resting potential?
Na high
+
+ + +
– – –
– – –
K high
+
a)
Na high
+
+ + +
– – –
– – –
K low
+
b)
Na low
+
+ + +
– – –
– – –
K high
+
c)
Na low
+
+ + +
– – –
– – –
K low
+
d)
+ + +
++ +
10. During recovery, nerve fiber becomes
a) Positively charged on outside and
negatively charged on inside
b) Positively charged on both outside and
inside
c) Negatively charged on outside and
positively charged on inside
d) Negatively charged on both outside and
inside
3. Pick out the incorrect statement?
a) Myelinated nerve fibers are found in
spinal and cranial nerve
b) Unmyelinated nerve fiber is enclosed by
a schwann cells
c) In resting stage the axonal membrane
is comparatively more permeable to
potassium ion and nearly impermeable
to sodium ions
d) Axolemma is more permeable to
negatively charged protein present in the
axoplasm
4. When a neuron is in resting state i.e. not
conducting any impulse, the axonal
membrane is
a) Equally permeable to both Na
+
and K
+
ions
b) Impermeable to both Na
+
and K
+
ions
c) Comparatively more permeable to K
+
ions and nearly impermeable to Na
+
ions
d) Comparatively more permeable to Na
+
ions and nearly impermeable to K
+
ions
5. Saltatory conduction is superior to
uninterrupted conduction because of
a) Less energy required
b) More speed
c) Less Na
+
/K
+
pump
d) All of the above
6. If dorsal nerve of spinal cord is broken down
then its effect is
a) No impulse is transmitted
b) Impulse is transmitted but slowly
c) Impulse is transmitted fast
d) No effect on impulse
7. An action potential in the nerve fibers is
produced when positive and negative
charges on the outside and the inside of the
axon membrane are reversed, because
a) More K
+
enters the axon as compared
to sodium ions leaving it
b) More Na
+
enters the axon as compared
to K
+
leaving it
c) All K
+
leaving the axon
d) All Na
+
enters the axon
8. Alzheimer’s disease in humans is
associated with deficiency of
a) Dopamine
b) Glutamic acid
c) Acetylcholine
d) Gamma amino butyric acid (GABA)
9. Which of the following diagram illustrates
the distribution of Na
+
and K
+
ions in a
section of non myelinated axon which is at
resting potential?
Na high
+
+ + +
– – –
– – –
K high
+
a)
Na high
+
+ + +
– – –
– – –
K low
+
b)
Na low
+
+ + +
– – –
– – –
K high
+
c)
Na low
+
+ + +
– – –
– – –
K low
+
d)
+ + +
++ +
10. During recovery, nerve fiber becomes
a) Positively charged on outside and
negatively charged on inside
b) Positively charged on both outside and
inside
c) Negatively charged on outside and
positively charged on inside
d) Negatively charged on both outside and
inside
26
11. Which of the following cranial nerves of
human are mixed in nature
a) Vagus and trigeminal
b) Optic and vagus
c) Auditory and olfactory
d) Trochlear and vagus
12. During the transmission of nerve impulse
through a nerve fiber, the potential on the
inner side of the plasma membrane has
which type of electric charge?
a) First positive, then negative and continue
to be negative
b) First negative, then positive and continue
to be positive
c) First positive, then negative and again
back to positive
d) First negative, then positive and again
back to negative
13. Pacinian corpuscles occur in the skin of
certain part of body in mammals are
a) Pain receptor
b) Naked tactile receptors
c) Gland type
d) Encapsulated tactile receptors
14. Neuropeptides are
a) Neurotransmitter chemicals
b) Neuroglia
c) Products of the choroid plexuses
d) Nutrients for brain tissue
15. These processes occurs during
repolarization of nerve fibers
A) Open Na
+
channel
B) Closed Na
+
channel
C) Closed K
+
channel
D) Open K
+
channel
a) (B) and (D) b) (A) and (C)
c) (B) and (C) d) (A) and (B)
16. Unidirectional transmission of a nerve
impulse through synapse fiber is due to
a) Nerve fiber is insulated by a medullary
sheath
b) Sodium pump starts operating only at the
cyton and then continues into the nerve
fiber
c) Neurotransmitters are released by
dendrites and not by axon endings
d) Neurotransmitters are released by the
axon endings and not by dendrites
17. Unipolar nerve cells can be traced in
a) Spinal ganglion cells
b) Retina cell
c) Motor neurons of spinal cord
d) Vertebrate embryo
18. Sympathetic nervous system is also known
as
a) Cranial b) Craniosacral
c) Thoracolumbar d) None of these
19. W hich of the following is dominant
intracellular anion?
a) Potassium b) Chloride
c) Phosphate d) Calcium
20. When the axons membrane is positively
charged outside and negatively charged
inside, then the condition is known as
a) Action potential
b) Resting potential
c) Active potential
d) Differential potential
21. When nerve fibers are stimulated the inside
of the membrane becomes
a) Filled with acetylcholine
b) Negatively charged
c) Positively charged
d) Neutral
11. Which of the following cranial nerves of
human are mixed in nature
a) Vagus and trigeminal
b) Optic and vagus
c) Auditory and olfactory
d) Trochlear and vagus
12. During the transmission of nerve impulse
through a nerve fiber, the potential on the
inner side of the plasma membrane has
which type of electric charge?
a) First positive, then negative and continue
to be negative
b) First negative, then positive and continue
to be positive
c) First positive, then negative and again
back to positive
d) First negative, then positive and again
back to negative
13. Pacinian corpuscles occur in the skin of
certain part of body in mammals are
a) Pain receptor
b) Naked tactile receptors
c) Gland type
d) Encapsulated tactile receptors
14. Neuropeptides are
a) Neurotransmitter chemicals
b) Neuroglia
c) Products of the choroid plexuses
d) Nutrients for brain tissue
15. These processes occurs during
repolarization of nerve fibers
A) Open Na
+
channel
B) Closed Na
+
channel
C) Closed K
+
channel
D) Open K
+
channel
a) (B) and (D) b) (A) and (C)
c) (B) and (C) d) (A) and (B)
16. Unidirectional transmission of a nerve
impulse through synapse fiber is due to
a) Nerve fiber is insulated by a medullary
sheath
b) Sodium pump starts operating only at the
cyton and then continues into the nerve
fiber
c) Neurotransmitters are released by
dendrites and not by axon endings
d) Neurotransmitters are released by the
axon endings and not by dendrites
17. Unipolar nerve cells can be traced in
a) Spinal ganglion cells
b) Retina cell
c) Motor neurons of spinal cord
d) Vertebrate embryo
18. Sympathetic nervous system is also known
as
a) Cranial b) Craniosacral
c) Thoracolumbar d) None of these
19. W hich of the following is dominant
intracellular anion?
a) Potassium b) Chloride
c) Phosphate d) Calcium
20. When the axons membrane is positively
charged outside and negatively charged
inside, then the condition is known as
a) Action potential
b) Resting potential
c) Active potential
d) Differential potential
21. When nerve fibers are stimulated the inside
of the membrane becomes
a) Filled with acetylcholine
b) Negatively charged
c) Positively charged
d) Neutral
27
22. Pre ganglionic sympathetic fibers are
a) Andrenergic b) Cholinergic
c) Hypergonic d) Synergic
23. During synaptic transmission of nerve
impulse neurotransmitter (P) is released
from synaptic vesicles by the action of ions
(Q). Choose the correct P and Q
a) P - acetylcholine, Q - Ca
2+
b) P - acetylcholine, Q - Na
+
c) P - GABA, Q - Na
+
d) P - Cholinesterase, Q - Ca
2+
24. Which nerve is purely motor?
a) Abducens b) Trigeminal
c) Olfactory d) Vagus
25. Unidirectional transmission of a nerve
impulse through nerve fiber is due to the
fact that
a) Nerve fiber is insulated by a medullary
sheath
b) Sodium pump starts operating only at the
cyton and then continues into the nerve
fiber
c) Neurotransmitters are released by
dendrites and not by axon endings
d) Neurotransmitters are released by the
axon endings and not by dendrites
26. Ventral root of spinal nerve is composed of
somatic
a) Motor and visceral sensory fibers
b) Sensory and visceral sensory fibers
c) Motor and visceral motor fibers
d) Sensory and visceral motor fibers
27. One of the examples of the action of the
autonomous nervous system is
a) Knee jerk response
b) Pupillary reflex
c) Swallowing of food
d) Peristalsis of the intestines
28. Trigeminal is
a) Motor in nature
b) Sensory
c) Mixed
d) All of these
29. If myelin sheath is continue in myelinated
nerve fiber than what will happen in neuronal
conduction
a) Velocity is increased
b) Conduction is slow
c) Conduction is stopped
d) No effect
30. Sympathetic nerves in mammals develop
from
a) Sacral region
b) Cervical region
c) Thoracic-lumbar region
d) 3
rd
, 7
th
, 9
th
, 10
th
cranial nerves
31. During refractory period
a) Nerve transmits impulse very slowly
b) Nerve cannot transmit impulse
c) Nerve transmits impulses very rapidly
d) None of the above
22. Pre ganglionic sympathetic fibers are
a) Andrenergic b) Cholinergic
c) Hypergonic d) Synergic
23. During synaptic transmission of nerve
impulse neurotransmitter (P) is released
from synaptic vesicles by the action of ions
(Q). Choose the correct P and Q
a) P - acetylcholine, Q - Ca
2+
b) P - acetylcholine, Q - Na
+
c) P - GABA, Q - Na
+
d) P - Cholinesterase, Q - Ca
2+
24. Which nerve is purely motor?
a) Abducens b) Trigeminal
c) Olfactory d) Vagus
25. Unidirectional transmission of a nerve
impulse through nerve fiber is due to the
fact that
a) Nerve fiber is insulated by a medullary
sheath
b) Sodium pump starts operating only at the
cyton and then continues into the nerve
fiber
c) Neurotransmitters are released by
dendrites and not by axon endings
d) Neurotransmitters are released by the
axon endings and not by dendrites
26. Ventral root of spinal nerve is composed of
somatic
a) Motor and visceral sensory fibers
b) Sensory and visceral sensory fibers
c) Motor and visceral motor fibers
d) Sensory and visceral motor fibers
27. One of the examples of the action of the
autonomous nervous system is
a) Knee jerk response
b) Pupillary reflex
c) Swallowing of food
d) Peristalsis of the intestines
28. Trigeminal is
a) Motor in nature
b) Sensory
c) Mixed
d) All of these
29. If myelin sheath is continue in myelinated
nerve fiber than what will happen in neuronal
conduction
a) Velocity is increased
b) Conduction is slow
c) Conduction is stopped
d) No effect
30. Sympathetic nerves in mammals develop
from
a) Sacral region
b) Cervical region
c) Thoracic-lumbar region
d) 3
rd
, 7
th
, 9
th
, 10
th
cranial nerves
31. During refractory period
a) Nerve transmits impulse very slowly
b) Nerve cannot transmit impulse
c) Nerve transmits impulses very rapidly
d) None of the above
28
ANSWER KEYS
Simple Questions
1.d 2.a 3.c 4.a 5.b 6.a 7.c 8.a 9.b 10.a 11.b 12.d
13.a 14.c 15.c 16.c 17.a 18.c 19.a 20.b 21.b 22.a 23.b 24.b
25.a 26.b 27a 28.d 29.c 30.b 31.b 32.c 33.d
Difficult Questions
1.c 2.c 3.b 4.c 5.d 6.a 7.b 8.c 9.a 10.a 11.a 12.d
13.b 14.a 15.a 16.d 17.a 18.c 19.c 20.b 21.c 22.b 23.a 24.a
25.d 26.c 27.d 28.d 29.c 30.c 31.b
ANSWER KEYS
Simple Questions
1.d 2.a 3.c 4.a 5.b 6.a 7.c 8.a 9.b 10.a 11.b 12.d
13.a 14.c 15.c 16.c 17.a 18.c 19.a 20.b 21.b 22.a 23.b 24.b
25.a 26.b 27a 28.d 29.c 30.b 31.b 32.c 33.d
Difficult Questions
1.c 2.c 3.b 4.c 5.d 6.a 7.b 8.c 9.a 10.a 11.a 12.d
13.b 14.a 15.a 16.d 17.a 18.c 19.c 20.b 21.c 22.b 23.a 24.a
25.d 26.c 27.d 28.d 29.c 30.c 31.b
29
1. Which of the following statements is false
about the electrical synapse?
I) At electrical synapses, the membranes
of pre and post synaptic neurons are in
very close proximity.
II) Electrical current can flow directly from
one neuron into the other across the
synapses.
III) Transmission of an impulse across
electrical synapses is very similar to
impulse conduction along single axon.
IV) Electrical synapses pass electrical signal
between cells with the use of Ach.
V) Electrical synapses are fast.
VI) Electrical synapses are rare in our
system.
a) I and II b) Only II
c) Only IV d) Only V
2. Five events in the transmission of nerve
impulse across the synapse are given below
A) Opening of specific ion channels allows
the entry of ions, a new action potential
is generated in the post synaptic neuron.
B) Neurotransmitter binds to the receptor
on post-synaptic membrane.
C) Synaptic vesicle fuses with pre-synaptic
membrane, neurotransmitter releases
into synaptic cleft.
D) Depolarization of presynaptic
membrane.
E) Arrival of action potential at axon
terminal.
In which sequence to the events occur?
a) E
DCBA
b) ABCDE
c) ABDCE
d) EDCAB
DPP - 1
3. Which role of neuron regarding different
kinds of stimuli is absent? a) Detect b) Receive
c) Transmit d) Protect
4. During repolarization of nerve
a) K
+
gates close and Na
+
gates open.
b) Na
+
channels are closed and K
+
channels are opened
c) Both gates remain open d) Both K
+
and Na
+
gates are closed
5. Synaptic vesicles are found in
a) Presynaptic neuron b) Postsynaptic neuron
c) Synaptic cleft
d) None of these
6. When a neuron is not conducting any
impulse i.e. resting, the axonal membrane
is
a) Comparatively more permeable to K
+
and impermeable (nearly impermeable)
to Na
+
b) Impermeable to negatively charged
proteins present in the axoplasm
c) (a) and (b) both
d) More permeable to Na
+
ions than K
+
ion
7. Which one of the following statements is
correct?
a) Neither hormones control neural activity
nor the neuron control endocrine activity
b) Endocrine glands regulate neural activity,
but not vice versa
c) Neurons regulate endocrine activity, but
not vice versa
d) Endocrine glands regulate neural activity,
and nervous system regulates endocrine
glands
1. Which of the following statements is false
about the electrical synapse?
I) At electrical synapses, the membranes
of pre and post synaptic neurons are in
very close proximity.
II) Electrical current can flow directly from
one neuron into the other across the
synapses.
III) Transmission of an impulse across
electrical synapses is very similar to
impulse conduction along single axon.
IV) Electrical synapses pass electrical signal
between cells with the use of Ach.
V) Electrical synapses are fast.
VI) Electrical synapses are rare in our
system.
a) I and II b) Only II
c) Only IV d) Only V
2. Five events in the transmission of nerve
impulse across the synapse are given below
A) Opening of specific ion channels allows
the entry of ions, a new action potential
is generated in the post synaptic neuron.
B) Neurotransmitter binds to the receptor
on post-synaptic membrane.
C) Synaptic vesicle fuses with pre-synaptic
membrane, neurotransmitter releases
into synaptic cleft.
D) Depolarization of presynaptic
membrane.
E) Arrival of action potential at axon
terminal.
In which sequence to the events occur?
a) E
DCBA
b) ABCDE
c) ABDCE
d) EDCAB
DPP - 1
3. Which role of neuron regarding different
kinds of stimuli is absent? a) Detect b) Receive
c) Transmit d) Protect
4. During repolarization of nerve
a) K
+
gates close and Na
+
gates open.
b) Na
+
channels are closed and K
+
channels are opened
c) Both gates remain open d) Both K
+
and Na
+
gates are closed
5. Synaptic vesicles are found in
a) Presynaptic neuron b) Postsynaptic neuron
c) Synaptic cleft
d) None of these
6. When a neuron is not conducting any
impulse i.e. resting, the axonal membrane
is
a) Comparatively more permeable to K
+
and impermeable (nearly impermeable)
to Na
+
b) Impermeable to negatively charged
proteins present in the axoplasm
c) (a) and (b) both
d) More permeable to Na
+
ions than K
+
ion
7. Which one of the following statements is
correct?
a) Neither hormones control neural activity
nor the neuron control endocrine activity
b) Endocrine glands regulate neural activity,
but not vice versa
c) Neurons regulate endocrine activity, but
not vice versa
d) Endocrine glands regulate neural activity,
and nervous system regulates endocrine
glands
30
8. Which of the statement is false regarding
synapse?
a) Synapse is formed by 2 membrane first
pre-synaptic membrane of synaptic knob
and second post synaptic membrane of
dendrite
b) Synaptic membrane always be
separated by a gap called synaptic cleft
c) Electrical synapse in very similar to
impulse conduction along a single axon
d) In chemical synapse, neurotransmitter
is released and either excitatory or
inhibitory potential is generated on post
synaptic membrane
9. Synapse is bringing together of two
a) Venules b) Veins
c) Arteries d) Neurons
10. Node of Ranvier occurs where
a) Nerve is covered with myelin sheath
b) Neurilemma is discontinuous
c) Neurilemma and myelin sheath are
discontinuous
d) Myelin sheath is discontinuous
8. Which of the statement is false regarding
synapse?
a) Synapse is formed by 2 membrane first
pre-synaptic membrane of synaptic knob
and second post synaptic membrane of
dendrite
b) Synaptic membrane always be
separated by a gap called synaptic cleft
c) Electrical synapse in very similar to
impulse conduction along a single axon
d) In chemical synapse, neurotransmitter
is released and either excitatory or
inhibitory potential is generated on post
synaptic membrane
9. Synapse is bringing together of two
a) Venules b) Veins
c) Arteries d) Neurons
10. Node of Ranvier occurs where
a) Nerve is covered with myelin sheath
b) Neurilemma is discontinuous
c) Neurilemma and myelin sheath are
discontinuous
d) Myelin sheath is discontinuous
31
2.1 CENTRAL NERVOUS SYSTEM
It includes the brain and the spinal cord. It develops from neural tube in intrauterine life (I.U.L).
Anterior part of neural tube develops into brain while caudal part of neural tube develops into spinal
cord. Brain’s approximately 70 – 80% part of brain develops in 2 years of age and complete
development is achieved in 6 years of age and spinal cord develops completely in 4 to 5 years of
age.
2.1.1 Brain
It is situated in cranial box which is made up of 1 frontal bone, 2 parietal bones, 2 temporal bone, 1
occipital bone. The weight of brain of a adult man is 1400 gm and of female is 1250 gm.
A. Brain meninges:
Brain is covered by three membranes of connective tissue termed as meninges or menix.
Superior
sagittal sinus
Subdural space
Subarachnoid space
Skin of scalp
Periosteum
Bone of skull
Periosteal
Meningeal
Dura
mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Meninges
UNIT 2 - NERVOUS SYSTEM II
Endosteal
Duramater
Meningeal
Arachnoid
Piamater
Cerebral cortex
Cranial venous sinus
Arachnoid villi
Subdural
space
Subarachnoid
space
Meningeal layer
2.1 CENTRAL NERVOUS SYSTEM
It includes the brain and the spinal cord. It develops from neural tube in intrauterine life (I.U.L).
Anterior part of neural tube develops into brain while caudal part of neural tube develops into spinal
cord. Brain’s approximately 70 – 80% part of brain develops in 2 years of age and complete
development is achieved in 6 years of age and spinal cord develops completely in 4 to 5 years of
age.
2.1.1 Brain
It is situated in cranial box which is made up of 1 frontal bone, 2 parietal bones, 2 temporal bone, 1
occipital bone. The weight of brain of a adult man is 1400 gm and of female is 1250 gm.
A. Brain meninges:
Brain is covered by three membranes of connective tissue termed as meninges or menix.
Superior
sagittal sinus
Subdural space
Subarachnoid space
Skin of scalp
Periosteum
Bone of skull
Periosteal
Meningeal
Dura
mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood vessel
Falx cerebri
(in longitudinal
fissure only)
Meninges
UNIT 2 - NERVOUS SYSTEM II
Endosteal
Duramater
Meningeal
Arachnoid
Piamater
Cerebral cortex
Cranial venous sinus
Arachnoid villi
Subdural
space
Subarachnoid
space
Meningeal layer
32
(i) Durameter: The first and the outermost membrane, thick, very strong and non-elastic. It is
made up of collagen fibers and attached with the innermost surface of the cranium. It is
double layered: outer endosteal layer which is closely attached with inner most surface of
cranium and no space is found between skull and durameter (no epidural space). Inner
meningeal layer is related with the other meninges of brain. Both layers are vascular and
generally fused with each other, but at some places these are separated from one another
and form a sinus called cranial venous sinus. These sinuses are filled with venous blood.
(ii) Arachnoid: It is middle, thin and delicate membrane, made up of connective tissue, found
only in mammals. It is non-vascular layer. In front of cranial venous sinus, it becomes folded,
these folds called Arachnoid villi. These villi reabsorb the cerebrospinal fluid (CSF) from
sub arachnoid space and pour it into cranial venous sinuses.
(iii) Piameter: It is innermost, thin and transparent membrane, made up of connective tissue.
Dense network of blood capillaries are found in it. It is firmly adhered to the brain. Piameter
and arachnoid layer at some places fuse together to form leptomeninges. Piameter merges
into sulci of brain and densely adhere to it. At some places it directly merges in the brain and
called telachoroidea which form the choroid plexus in the ventricle of brain.
TARGET POINTS
Subdural space: Space between durameter and arachnoid that is filled with serous fluid.
Subarachnoid space: Space between arachnoid and piameter is filled with CSF. Cranial nerves
also pass through this space.
Meningitis: Any inflammation of menix that may be caused by viruses, bacteria or protozoa.
In the brain of frog only 2 meninges are present. Arachnoid is absent while in rabbit, man and
mammals – 3 meninges are present.
Increase in the amount of cerebro spinal fluid is a diseased condition termed as the
hydrocephalus.
Piameter is the most vascular and conducting and provides nutrition.
Around the brain of fishes, only one menix is found called “menix primitive”.
B. Cerebrospinal fluid (CSF):
Clear and alkaline in nature just like lymph.
Has protein (albumin, globulin), glucose, cholesterol, urea, bicarbonates, sulphates and
chlorides of Na, K. Protein and cholesterol concentration is lesser than plasma and Cl
-
concentration is higher than plasma.
In a healthy man, in 24 hours, 500 ml of CSF is formed and absorbed by arachnoid villi. At a
time total volume of CSF is 150 ml.
CSF is present in ventricle of brain, subarachnoid space of brain and spinal cord.
(i) Durameter: The first and the outermost membrane, thick, very strong and non-elastic. It is
made up of collagen fibers and attached with the innermost surface of the cranium. It is
double layered: outer endosteal layer which is closely attached with inner most surface of
cranium and no space is found between skull and durameter (no epidural space). Inner
meningeal layer is related with the other meninges of brain. Both layers are vascular and
generally fused with each other, but at some places these are separated from one another
and form a sinus called cranial venous sinus. These sinuses are filled with venous blood.
(ii) Arachnoid: It is middle, thin and delicate membrane, made up of connective tissue, found
only in mammals. It is non-vascular layer. In front of cranial venous sinus, it becomes folded,
these folds called Arachnoid villi. These villi reabsorb the cerebrospinal fluid (CSF) from
sub arachnoid space and pour it into cranial venous sinuses.
(iii) Piameter: It is innermost, thin and transparent membrane, made up of connective tissue.
Dense network of blood capillaries are found in it. It is firmly adhered to the brain. Piameter
and arachnoid layer at some places fuse together to form leptomeninges. Piameter merges
into sulci of brain and densely adhere to it. At some places it directly merges in the brain and
called telachoroidea which form the choroid plexus in the ventricle of brain.
TARGET POINTS
Subdural space: Space between durameter and arachnoid that is filled with serous fluid.
Subarachnoid space: Space between arachnoid and piameter is filled with CSF. Cranial nerves
also pass through this space.
Meningitis: Any inflammation of menix that may be caused by viruses, bacteria or protozoa.
In the brain of frog only 2 meninges are present. Arachnoid is absent while in rabbit, man and
mammals – 3 meninges are present.
Increase in the amount of cerebro spinal fluid is a diseased condition termed as the
hydrocephalus.
Piameter is the most vascular and conducting and provides nutrition.
Around the brain of fishes, only one menix is found called “menix primitive”.
B. Cerebrospinal fluid (CSF):
Clear and alkaline in nature just like lymph.
Has protein (albumin, globulin), glucose, cholesterol, urea, bicarbonates, sulphates and
chlorides of Na, K. Protein and cholesterol concentration is lesser than plasma and Cl
-
concentration is higher than plasma.
In a healthy man, in 24 hours, 500 ml of CSF is formed and absorbed by arachnoid villi. At a
time total volume of CSF is 150 ml.
CSF is present in ventricle of brain, subarachnoid space of brain and spinal cord.
33
Formation: Mainly in choroid
plexus of lateral ventricles,
minor quantity is formed in III
rd
ventricle and IV
th
ventricle.
Collection of CSF for any
investigation is done by lumbar
puncture (LP). It is done at L
3
–
L
4
region. Spinal anesthesia is
also given by L.P.
CSF flow through the ventricles
Superior sagittal sinus
Choroid plexus
Interventricular foramen
Third ventricle
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Central canal
Arachnoid granulation
Subarachnoid space
Meningeal dura mater
Right lateral ventricle
Functions of CSF:
Protection of brain: Acts as shock absorbing medium and works as cushion.
It provides buoyancy to the brain, so net weight of the brain is reduced from about 1.4 kg to
about 0.18 kg.
Excretion of waste products.
Endocrine medium for brain to transport hormones to different areas of the brain.
C. Brain divisions
Ependymal
cells
Capillary
Connective
tissue of
pia mater
Wastes and
unnecessary
solutes absorbed
Cavity of
ventricle
CSF forms as a filtrate
containing glucose, oxygen,
vitamins, and bone
(Na , CI, Mg, etc.)
+
Section
of choroid
plexus
Cerebrospinal fluid (CSF) - choroid plexus
Fore brain Cerebrum, diencephalon.
Mid brain Optic lobes and crura cerebri.
Hind brain Pons, Cerebellum, medulla.
Formation: Mainly in choroid
plexus of lateral ventricles,
minor quantity is formed in III
rd
ventricle and IV
th
ventricle.
Collection of CSF for any
investigation is done by lumbar
puncture (LP). It is done at L
3
–
L
4
region. Spinal anesthesia is
also given by L.P.
CSF flow through the ventricles
Superior sagittal sinus
Choroid plexus
Interventricular foramen
Third ventricle
Cerebral aqueduct
Lateral aperture
Fourth ventricle
Median aperture
Central canal
Arachnoid granulation
Subarachnoid space
Meningeal dura mater
Right lateral ventricle
Functions of CSF:
Protection of brain: Acts as shock absorbing medium and works as cushion.
It provides buoyancy to the brain, so net weight of the brain is reduced from about 1.4 kg to
about 0.18 kg.
Excretion of waste products.
Endocrine medium for brain to transport hormones to different areas of the brain.
C. Brain divisions
Ependymal
cells
Capillary
Connective
tissue of
pia mater
Wastes and
unnecessary
solutes absorbed
Cavity of
ventricle
CSF forms as a filtrate
containing glucose, oxygen,
vitamins, and bone
(Na , CI, Mg, etc.)
+
Section
of choroid
plexus
Cerebrospinal fluid (CSF) - choroid plexus
Fore brain Cerebrum, diencephalon.
Mid brain Optic lobes and crura cerebri.
Hind brain Pons, Cerebellum, medulla.
34
During embryonic stage, brain develops from three hollow vesicles:
Forebrain develops form prosencephalon
Mid brain develops from mesencephalon
Hind brain develops from rhombencephalon
Rhinencephalon (Olfactory lobe)
Telencephalon (Cerebrum)
Diencephalon
Metencephalon
(Pons, Cerebellum)
Myelencephalon
(Medulla oblongata (M.O.))
C.a. Fore brain
(i) Cerebrum
Frontal lobe
Parietal lobe
Temporal lobe
Occipital lobe
Parietal operculum
Frontal operculum
Orbital operculum
Insula
(island
of Reil)
Short gyri
Central sulcus
Limen
Long gyrus
Circular sulcus
Temporal operculum
First and most developed part of brain. Makes 2/3 part of total brain.
Consists of two cerebral hemispheres on the dorsal surface. A longitudinal groove (median
fissure) is present between two cerebral hemispheres. Both the cerebral hemispheres are
partially connected with each other by curved thick nerve fibers called corpus callosum.
Corpus callosum is the largest commissure of brain. It is the exclusive feature of mammals.
Curved thick band of white nerve fiber are situated between two cerebral hemispheres in the
median fissure.
Anterior truncated part of corpus callosum is called Genu while posterior truncated part is
called splenium.
An oblique band is formed by body of corpus callosum and it goes towards Genu called
fornix.
During embryonic stage, brain develops from three hollow vesicles:
Forebrain develops form prosencephalon
Mid brain develops from mesencephalon
Hind brain develops from rhombencephalon
Rhinencephalon (Olfactory lobe)
Telencephalon (Cerebrum)
Diencephalon
Metencephalon
(Pons, Cerebellum)
Myelencephalon
(Medulla oblongata (M.O.))
C.a. Fore brain
(i) Cerebrum
Frontal lobe
Parietal lobe
Temporal lobe
Occipital lobe
Parietal operculum
Frontal operculum
Orbital operculum
Insula
(island
of Reil)
Short gyri
Central sulcus
Limen
Long gyrus
Circular sulcus
Temporal operculum
First and most developed part of brain. Makes 2/3 part of total brain.
Consists of two cerebral hemispheres on the dorsal surface. A longitudinal groove (median
fissure) is present between two cerebral hemispheres. Both the cerebral hemispheres are
partially connected with each other by curved thick nerve fibers called corpus callosum.
Corpus callosum is the largest commissure of brain. It is the exclusive feature of mammals.
Curved thick band of white nerve fiber are situated between two cerebral hemispheres in the
median fissure.
Anterior truncated part of corpus callosum is called Genu while posterior truncated part is
called splenium.
An oblique band is formed by body of corpus callosum and it goes towards Genu called
fornix.
35
A small cavity is developed among body of callosum, Genu and fornix called as V
th
ventricle
or pseudocoel. This ventricle is covered by a thin membrane called as septum lucidum.
Each cerebral hemisphere is divided into 5 lobes – Anterior, middle, posterior, lateral and
insula lobes.
– Anterior lobe is also called frontal lobe (largest lobe).
– Middle lobe is also called parietal lobe.
– Central sulcus separates frontal lobe from parietal lobe.
– Lateral lobe or temporal lobe is separated from frontal lobe and parietal lobe by incomplete
sulcus called lateral sulcus.
– Posterior lobe is called occipital lobe, it is separated from parietal lobe by a sulcus called
parieto occipital sulcus.
In right handed person, left hemisphere is dominant while in left handed person right
hemisphere is dominant.
Many ridges (gyri) and grooves (sulci) are found on dorsal surface of cerebral hemisphere.
These cover the 2/3 part of cerebrum. Gyri and sulci are more developed in human being
thus, humans are most intelligent living beings.
Septum pellucidum
Head of caudate nucleus
Internal capsule
(anterior limb)
Corpus callosum
(genu)
Anterior hom
(lateral ventricle)
Amygdala
Hippocampus
Fornix
Corpus callosum
(splenium
Foramen
of monro
Putamen
Internal capsule
(genu)
Globus
pallidus
Internal capsule
(posterior limb)
Third ventricle
Thalamus
Tail of caudate nucleus
Transverse section of brain
A small cavity is developed among body of callosum, Genu and fornix called as V
th
ventricle
or pseudocoel. This ventricle is covered by a thin membrane called as septum lucidum.
Each cerebral hemisphere is divided into 5 lobes – Anterior, middle, posterior, lateral and
insula lobes.
– Anterior lobe is also called frontal lobe (largest lobe).
– Middle lobe is also called parietal lobe.
– Central sulcus separates frontal lobe from parietal lobe.
– Lateral lobe or temporal lobe is separated from frontal lobe and parietal lobe by incomplete
sulcus called lateral sulcus.
– Posterior lobe is called occipital lobe, it is separated from parietal lobe by a sulcus called
parieto occipital sulcus.
In right handed person, left hemisphere is dominant while in left handed person right
hemisphere is dominant.
Many ridges (gyri) and grooves (sulci) are found on dorsal surface of cerebral hemisphere.
These cover the 2/3 part of cerebrum. Gyri and sulci are more developed in human being
thus, humans are most intelligent living beings.
Septum pellucidum
Head of caudate nucleus
Internal capsule
(anterior limb)
Corpus callosum
(genu)
Anterior hom
(lateral ventricle)
Amygdala
Hippocampus
Fornix
Corpus callosum
(splenium
Foramen
of monro
Putamen
Internal capsule
(genu)
Globus
pallidus
Internal capsule
(posterior limb)
Third ventricle
Thalamus
Tail of caudate nucleus
Transverse section of brain
36
Cingulate gyrus
Interthalamic
adhesion
Septum pellucidum
Corpus callosum
Lateral ventricle
Anterior commissure
Optic nerve and chiasma
Pituitary gland
Mammillary body
Uncum
Pons
Medulla oblongata
Fourth ventricle
Cerebellum
Inferior colliculus
Superior colliculus
Pineal body
Calcarine sulcus
Parietooccipital sulcus
Thalamus
Choroid plexus
Fornix
Central sulcus
Sagittal section of brain
(ii) Diencephalon
Small and posterior part of fore brain, covered by cerebrum.
It consists of thalamus, hypothalamus, epithalamus and metathalamus.
Thalamus forms the upper lateral walls of Diencephalon (80% part). It is the gate keeper of
brain and acts as a relay center. It receives all sensory impulses from all body parts and
these impulses are send to the cerebral cortex.
Hypothalamus forms the lower or ventral part of Diencephalon. A cross like structure is found
on anterior surface called optic chiasma. Corpus mammillare / Corpus albicans/
mammillary body is found on the posterior part. It is a character of mammalian brain.
Epithalamus – Forms the roof of diencephalon. Pineal body (Epiphysis cerebri) is found in
epithalamus.
Metathalamus consists of medial geniculate body and lateral geniculate body. It is located
in the floor of Diencephalon.
C.b. Mid brain
Small and contracted part of brain.
Anterior part contains two longitudinal myelinated nerve fibers peduncles called cerebral
peduncles/ crus cerebri / crura cerebri.
Cingulate gyrus
Interthalamic
adhesion
Septum pellucidum
Corpus callosum
Lateral ventricle
Anterior commissure
Optic nerve and chiasma
Pituitary gland
Mammillary body
Uncum
Pons
Medulla oblongata
Fourth ventricle
Cerebellum
Inferior colliculus
Superior colliculus
Pineal body
Calcarine sulcus
Parietooccipital sulcus
Thalamus
Choroid plexus
Fornix
Central sulcus
Sagittal section of brain
(ii) Diencephalon
Small and posterior part of fore brain, covered by cerebrum.
It consists of thalamus, hypothalamus, epithalamus and metathalamus.
Thalamus forms the upper lateral walls of Diencephalon (80% part). It is the gate keeper of
brain and acts as a relay center. It receives all sensory impulses from all body parts and
these impulses are send to the cerebral cortex.
Hypothalamus forms the lower or ventral part of Diencephalon. A cross like structure is found
on anterior surface called optic chiasma. Corpus mammillare / Corpus albicans/
mammillary body is found on the posterior part. It is a character of mammalian brain.
Epithalamus – Forms the roof of diencephalon. Pineal body (Epiphysis cerebri) is found in
epithalamus.
Metathalamus consists of medial geniculate body and lateral geniculate body. It is located
in the floor of Diencephalon.
C.b. Mid brain
Small and contracted part of brain.
Anterior part contains two longitudinal myelinated nerve fibers peduncles called cerebral
peduncles/ crus cerebri / crura cerebri.
37
Posterior part has four spherical projections called colliculus or optic lobes. Four colliculus
are collectively called as corpora quadrigemina (2 upper and 2 lower).
Only 2 colliculus or optic lobes are found in mid brain of frog called as corpora bigemina.
Cerebral aqueduct
Tectum
Tegmentum (reticular formation)
Superior colliculus
PAG
CN III
Medial lemniscus
Substantia nigra
Pars compacta
Cerebral peduncle
Occipito, parieto,
temporopontine fibers
Corticospinal fibers
Corticobulbar fibers
Frontopontine fibers
Root fibers
of CN III
Ventral tegmental area
Crus cerebri
Spinothalamic and
trigeminothalamic tracts
Red nucleus
Transverse section of midbrain
C.c. Hind brain
(i) Pons (Pons varolii)
Small spherical projection situated below the midbrain and on the upper side of medulla
oblongata.
Consists of many transverse and longitudinal nerve fibers. Transverse nerve fibers connect
with cerebellum (lateral lobes of cerebellum) while longitudinal fibers connect cerebrum to
M.O.
(ii) Cerebellum
Made up of 3 lobes [2 lateral lobes and 1 vermis (divided in 9 segments)].
Both lateral lobes are enlarged and spherical in shape, thus also called cerebellar hemisphere.
Due to this reason, regulation and coordination of voluntary muscle is more developed as
compared to other animals.
Three cerebellar peduncles are formed; superior cerebellar peduncle is attached with mid
brain. Middle cerebellar peduncle is attached with pons and inferior cerebellar peduncle
is attached with M.O.
(iii) Medulla oblongata (M.O): Posterior part of brain, tubular and cylindrical in shape.
Posterior part has four spherical projections called colliculus or optic lobes. Four colliculus
are collectively called as corpora quadrigemina (2 upper and 2 lower).
Only 2 colliculus or optic lobes are found in mid brain of frog called as corpora bigemina.
Cerebral aqueduct
Tectum
Tegmentum (reticular formation)
Superior colliculus
PAG
CN III
Medial lemniscus
Substantia nigra
Pars compacta
Cerebral peduncle
Occipito, parieto,
temporopontine fibers
Corticospinal fibers
Corticobulbar fibers
Frontopontine fibers
Root fibers
of CN III
Ventral tegmental area
Crus cerebri
Spinothalamic and
trigeminothalamic tracts
Red nucleus
Transverse section of midbrain
C.c. Hind brain
(i) Pons (Pons varolii)
Small spherical projection situated below the midbrain and on the upper side of medulla
oblongata.
Consists of many transverse and longitudinal nerve fibers. Transverse nerve fibers connect
with cerebellum (lateral lobes of cerebellum) while longitudinal fibers connect cerebrum to
M.O.
(ii) Cerebellum
Made up of 3 lobes [2 lateral lobes and 1 vermis (divided in 9 segments)].
Both lateral lobes are enlarged and spherical in shape, thus also called cerebellar hemisphere.
Due to this reason, regulation and coordination of voluntary muscle is more developed as
compared to other animals.
Three cerebellar peduncles are formed; superior cerebellar peduncle is attached with mid
brain. Middle cerebellar peduncle is attached with pons and inferior cerebellar peduncle
is attached with M.O.
(iii) Medulla oblongata (M.O): Posterior part of brain, tubular and cylindrical in shape.
38
TARGET POINTS
Mid brain, pons and medulla are situated in one axis and called as brain stem.
The sensory and associated areas determine the shape, color, sound, taste and smell of
any object.
Motor area regulates muscular contraction.
Broca’s area: it is known as motor speech area. It is present in the lateral part of the frontal
lobe of the cerebrum. This area translates the written words into speech. If Broca’s area
gets destroyed the animal is unable to speak.
The temporal lobes of cerebrum regulate the mechanism of hearing.
Cerebrum is the center of following:
– Intelligence – Experience
– Emotion – Knowledge
– Will power – Voluntary control
– Memory – Laughing and weeping
– Consciousness – Defecation and micturition
Diencephalon is the center of carbohydrate metabolism and fat metabolism.
Cerebellum is made up of three layers and in the middle brain lobes of flask shaped cells called
the “Purkinje cells” are found.
D. Internal structure of brain
One pair of olfactory lobes are small spherical and solid in human brain. No ventricle is found
in it. Both olfactory lobes are separate with each other and embedded into the ventral surface
of both frontal lobes of cerebral hemispheres. Olfactory center is situated in the temporal
lobe.
Optic chiasma
Olfactory lobe
VENTRAL VIEW OF BRAIN
Lateral geniculate
body
Medial geniculate
body
Olfactory centre
Temporal lobe
Olfactory tract
Frontal lobe
Paracoel or
Lateral ventricle
Third ventricle
or diocoel
Cerebral queduct
or aqueduct of
sylvius or Iter
Fourth ventricle
Cerebrum
Diencephalon
Midbrain
Pons
Cerebellum
Medulla
oblongata
L.S. OF BRAIN
Interventricular foramen or
foramen of
monro
TARGET POINTS
Mid brain, pons and medulla are situated in one axis and called as brain stem.
The sensory and associated areas determine the shape, color, sound, taste and smell of
any object.
Motor area regulates muscular contraction.
Broca’s area: it is known as motor speech area. It is present in the lateral part of the frontal
lobe of the cerebrum. This area translates the written words into speech. If Broca’s area
gets destroyed the animal is unable to speak.
The temporal lobes of cerebrum regulate the mechanism of hearing.
Cerebrum is the center of following:
– Intelligence – Experience
– Emotion – Knowledge
– Will power – Voluntary control
– Memory – Laughing and weeping
– Consciousness – Defecation and micturition
Diencephalon is the center of carbohydrate metabolism and fat metabolism.
Cerebellum is made up of three layers and in the middle brain lobes of flask shaped cells called
the “Purkinje cells” are found.
D. Internal structure of brain
One pair of olfactory lobes are small spherical and solid in human brain. No ventricle is found
in it. Both olfactory lobes are separate with each other and embedded into the ventral surface
of both frontal lobes of cerebral hemispheres. Olfactory center is situated in the temporal
lobe.
Optic chiasma
Olfactory lobe
VENTRAL VIEW OF BRAIN
Lateral geniculate
body
Medial geniculate
body
Olfactory centre
Temporal lobe
Olfactory tract
Frontal lobe
Paracoel or
Lateral ventricle
Third ventricle
or diocoel
Cerebral queduct
or aqueduct of
sylvius or Iter
Fourth ventricle
Cerebrum
Diencephalon
Midbrain
Pons
Cerebellum
Medulla
oblongata
L.S. OF BRAIN
Interventricular foramen or
foramen of
monro
39
Except mid brain, cerebellum, pons and olfactory lobes complete brain is internally hollow.
Its cavity is lined by ependymal epithelium (ciliated columnar epithelium). Cavities of brain
are known as ventricles, filled with cerebrospinal fluid (C.S.F).
In humans, 1
st
and 2
nd
ventricles are considered as paracoel or lateral ventricles.
On the posterior side, both paracoel combine with each other and open into cavity of
Diencephalon through an aperture known as Foramen of Monro.
Cavity of diencephalon is known as 3
rd
ventricle or diocoel.
A tent shaped space or cavity present between anterior pons, medulla and posterior cerebellum
is called 4
th
ventricle.
3
rd
and 4
th
ventricles are connected with each other through a hollow tube known as Iter of
Aqueduct of sylvius.
4
th
ventricle continues in the metacoel and metacoel continues in the cavity of spinal cord
called neurocoel or central canal.
One aperture is found on dorsal surface of metacoel known as foramen of magendie.
Two apertures are found on lateral sides of metacoel known as Foramen of Luschka [1-1].
CSF of brain comes out from the foramen of Magendie and Luschka and is poured into sub
arachnoid space.
TARGET POINTS
In rabbit, cavity of olfactory lobe is hollow called as 1
st
ventricle or rhinocoel. Both rhinocoel
continue in cavity of cerebral hemisphere, known as 2
nd
ventricle or paracoel or lateral ventricle.
The optic lobes of frog are hollow and in them optocoel cavity is found. 2 optic lobes are
present. These are hollow and termed as corpora bigemina. In mammals, 4 solid optic lobes
are present.
The valve of vieussens joins the optic lobes with the cerebellum.
E. Histology of brain
On dorsal surface of cerebral hemisphere, gray matter becomes more thick and is known as
cerebral cortex/ Neopallium/ pallium.
W
G
Cerebrum
Diencephalon
Cerebellum
1
G
W
Spinal cord
Brain stem
2
G - Gray matter
W - White matte
Except mid brain, cerebellum, pons and olfactory lobes complete brain is internally hollow.
Its cavity is lined by ependymal epithelium (ciliated columnar epithelium). Cavities of brain
are known as ventricles, filled with cerebrospinal fluid (C.S.F).
In humans, 1
st
and 2
nd
ventricles are considered as paracoel or lateral ventricles.
On the posterior side, both paracoel combine with each other and open into cavity of
Diencephalon through an aperture known as Foramen of Monro.
Cavity of diencephalon is known as 3
rd
ventricle or diocoel.
A tent shaped space or cavity present between anterior pons, medulla and posterior cerebellum
is called 4
th
ventricle.
3
rd
and 4
th
ventricles are connected with each other through a hollow tube known as Iter of
Aqueduct of sylvius.
4
th
ventricle continues in the metacoel and metacoel continues in the cavity of spinal cord
called neurocoel or central canal.
One aperture is found on dorsal surface of metacoel known as foramen of magendie.
Two apertures are found on lateral sides of metacoel known as Foramen of Luschka [1-1].
CSF of brain comes out from the foramen of Magendie and Luschka and is poured into sub
arachnoid space.
TARGET POINTS
In rabbit, cavity of olfactory lobe is hollow called as 1
st
ventricle or rhinocoel. Both rhinocoel
continue in cavity of cerebral hemisphere, known as 2
nd
ventricle or paracoel or lateral ventricle.
The optic lobes of frog are hollow and in them optocoel cavity is found. 2 optic lobes are
present. These are hollow and termed as corpora bigemina. In mammals, 4 solid optic lobes
are present.
The valve of vieussens joins the optic lobes with the cerebellum.
E. Histology of brain
On dorsal surface of cerebral hemisphere, gray matter becomes more thick and is known as
cerebral cortex/ Neopallium/ pallium.
W
G
Cerebrum
Diencephalon
Cerebellum
1
G
W
Spinal cord
Brain stem
2
G - Gray matter
W - White matte
40
Outer part of cerebellum is made up of gray matter while inner part is of white matter. White
matter projects outside and forms a branched tree like structure known as Arbor Vitae.
Coroid plexus: Telachoroidea (Piameter which is merged in ventricle) + blood capillaries +
ependymal epithelium.
Site: Two major plexuses in lateral ventricles; 2 minor plexuses in 3
rd
ventricle while 1 minor
plexus in 4
th
ventricle.
Function: Formation of CSF by secretion of plasma.
Sometimes (congenitally or infection) aqueduct becomes blocked leading to improper
circulation of CSF and intra cranial pressure increases, head becomes enlarged, this condition
is called hydrocephalus.
Circulation: From the ventricles, CSF comes into subarachnoid space through foramen of
Magendie and Foramen of Luschka. In sub arachnoid space, CSF is absorbed by arachnoid
villi which pour it into cranial venous sinus. From venous sinus CSF enters in blood circulation.
Choroid plexusLateral ventricleForamen of monroDiocoelAqueduct
IV Ventricle
th
MetacoelForamen of megendie and
foramenof luschka
Arachnoid
space
Arachnoid
villi
Cranial venous sinusBlood circulation
F. Limbic system:
It is visible like a wish bone, tuning fork or liplike.
Limbic lobe (area of temporal lobe) + hippocampus + hypothalamus including septum + part
of thalamus + mammalary bodies + amygdaloid complex.
Functions of limbic system
– Behavior, emotion, rage and anger (hypothalamus, amygdaloid body)
– Recent memory and short term memory converts into long term memory. (hippocampal
lobe)
– Food habit (hypothalamus)
– Sexual behavior (hypothalamus)
– Olfaction (hippocampal lobe and limbic lobe)
Name of area Location Relation or analysis
Prefrontal cortex Frontal lobe Seat of intelligence, knowledge, creative
ideas, ability to abstract, memory (organ of mind).
Premotor area Frontal lobe Written center
Associated movement of eye, head and body
Control complex movement of jaw, tongue,
pharynx, larynx.
Outer part of cerebellum is made up of gray matter while inner part is of white matter. White
matter projects outside and forms a branched tree like structure known as Arbor Vitae.
Coroid plexus: Telachoroidea (Piameter which is merged in ventricle) + blood capillaries +
ependymal epithelium.
Site: Two major plexuses in lateral ventricles; 2 minor plexuses in 3
rd
ventricle while 1 minor
plexus in 4
th
ventricle.
Function: Formation of CSF by secretion of plasma.
Sometimes (congenitally or infection) aqueduct becomes blocked leading to improper
circulation of CSF and intra cranial pressure increases, head becomes enlarged, this condition
is called hydrocephalus.
Circulation: From the ventricles, CSF comes into subarachnoid space through foramen of
Magendie and Foramen of Luschka. In sub arachnoid space, CSF is absorbed by arachnoid
villi which pour it into cranial venous sinus. From venous sinus CSF enters in blood circulation.
Choroid plexusLateral ventricleForamen of monroDiocoelAqueduct
IV Ventricle
th
MetacoelForamen of megendie and
foramenof luschka
Arachnoid
space
Arachnoid
villi
Cranial venous sinusBlood circulation
F. Limbic system:
It is visible like a wish bone, tuning fork or liplike.
Limbic lobe (area of temporal lobe) + hippocampus + hypothalamus including septum + part
of thalamus + mammalary bodies + amygdaloid complex.
Functions of limbic system
– Behavior, emotion, rage and anger (hypothalamus, amygdaloid body)
– Recent memory and short term memory converts into long term memory. (hippocampal
lobe)
– Food habit (hypothalamus)
– Sexual behavior (hypothalamus)
– Olfaction (hippocampal lobe and limbic lobe)
Name of area Location Relation or analysis
Prefrontal cortex Frontal lobe Seat of intelligence, knowledge, creative
ideas, ability to abstract, memory (organ of mind).
Premotor area Frontal lobe Written center
Associated movement of eye, head and body
Control complex movement of jaw, tongue,
pharynx, larynx.
41
Limbic association area
Premotor cortex
Primary motor cortex
Central sulcus
Primary somatosensory cortex
Parietal lobe
Somatosensory
association cortex
Parieto-occipital sulcus
Occipital lobe
Visual
association area
Primary visual cortex
Calcarine
sulcus
Parahippocampal gyrus
Uncus
Primary
olfactory
cortex
Temporal lobe
Olfactory bulb
Olfactory tract
Fornix
Orbitofrontal cortex
Processes emotions related to personal and social interactions
Cingulate gyrus
Prefrontal cortex
Frontal eye field
Frontal eye field
Functional areas of cerebral cortex
Motor area Frontal lobe Analysis of all type of voluntary muscle
Frontal eye field Frontal lobe Responsible for conjugate movement of eye.
Opening and closing of eye lid.
Broca’s area Frontal lobe Analysis for speak if injury to this region
In right handed personIn Present of left side inability to speak (aphasia) even though
left handed person Present of right side muscle concerned are not paralyzed
(motor speech area)
Auditory area Temporal Analysis for sound
Olfactory Temporal or Analysis for smell
hippocampal gyrus
Wernicke’s area (sensory Temporal Analysis for language
area of speech) Sensory analysis for speech
Gustatory area Parietal Analysis for taste
Somesthetic area Parietal Analysis for touch, pressure, pain, knowledge
about position in space taking in information
from environment etc.
Angular gyrus Parietal Sensory analysis for writing
Occipital area Occipital Analysis for vision
Limbic association area
Premotor cortex
Primary motor cortex
Central sulcus
Primary somatosensory cortex
Parietal lobe
Somatosensory
association cortex
Parieto-occipital sulcus
Occipital lobe
Visual
association area
Primary visual cortex
Calcarine
sulcus
Parahippocampal gyrus
Uncus
Primary
olfactory
cortex
Temporal lobe
Olfactory bulb
Olfactory tract
Fornix
Orbitofrontal cortex
Processes emotions related to personal and social interactions
Cingulate gyrus
Prefrontal cortex
Frontal eye field
Frontal eye field
Functional areas of cerebral cortex
Motor area Frontal lobe Analysis of all type of voluntary muscle
Frontal eye field Frontal lobe Responsible for conjugate movement of eye.
Opening and closing of eye lid.
Broca’s area Frontal lobe Analysis for speak if injury to this region
In right handed personIn Present of left side inability to speak (aphasia) even though
left handed person Present of right side muscle concerned are not paralyzed
(motor speech area)
Auditory area Temporal Analysis for sound
Olfactory Temporal or Analysis for smell
hippocampal gyrus
Wernicke’s area (sensory Temporal Analysis for language
area of speech) Sensory analysis for speech
Gustatory area Parietal Analysis for taste
Somesthetic area Parietal Analysis for touch, pressure, pain, knowledge
about position in space taking in information
from environment etc.
Angular gyrus Parietal Sensory analysis for writing
Occipital area Occipital Analysis for vision
42
TARGET POINTS
Association area responsible for complex functions like inter sensory association, memory and
communications.
Reticular activating system: It is special sensory fibers which is situated in brain stem and
further go in to thalamus. It is related with consciousness, alertness and awakening. Therefore
it is also called gate keeper of consciousness.
G. Functions of brain
Olfactory lobe: It is supposed to be the center of smelling power. Its size is small in mammals
comparatively because most of its parts become a part of cerebrum (including olfactory tract)
some animals like sharks and dogs have well developed olfactory lobes.
Cerebral hemispheres: Controls and regulates different parts of brain. This is the center of
conscious senses, will power, voluntary movements, knowledge, memory, speech and thinking,
reasoning etc. different sense organs send impulses here, and analysis and coordination of
impulses is done then messages are transferred according to the reactions through voluntary
muscles. All the voluntary actions are controlled by cerebral hemispheres.
Diencephalon: Pineal body, situated in the epithalamus, controls the sexual maturity of animal.
Thalamus – Act as relay center for sensory stimulation. In lower animals, cerebral cortex is
not developed and thalamus acts as sensory center. It is related with RAS and also act as
limbic part.
Functions of hypothalamus: Thermoregulation, behavior and emotion, endocrine control,
biological clock system and ANS control.
Centers of animal feelings/ emotions like sleep, anger, (libido), hate, love, affection, and
temperature control pain, hunger, thirst and satisfaction in the hypothalamus.
Optic chiasma found in the hypothalamus carry optic impulses received from eyes to the
cerebral hemispheres. Animal becomes blind if this part is destroyed by chance.
Metathalamus: It is related with MGB and LGB: MGB is related with hearing and LGB related
with vision. Nerve fibers of concerning place go through metathalamus.
Mid brain: Four optic lobes or colliculus present, superior optic lobes are the main centers of
pupillary light reflexes inferior optic lobes are related with acoustic (sound) reflex action.
Crura cerebri controls the muscles of limbs.
Cerebellum: Impulses are received from different voluntary muscles, joints and controlling
of their movements. When alcohol is consumed in excess, the cerebellum gets affected; as
a result one cannot maintain balance and walking in disturbed.
Thus it is related with fine and skillful voluntary movement and also related with body
balance, equilibrium, posture and tone.
Pons regulates the breathing reaction through pneumotaxic center.
TARGET POINTS
Association area responsible for complex functions like inter sensory association, memory and
communications.
Reticular activating system: It is special sensory fibers which is situated in brain stem and
further go in to thalamus. It is related with consciousness, alertness and awakening. Therefore
it is also called gate keeper of consciousness.
G. Functions of brain
Olfactory lobe: It is supposed to be the center of smelling power. Its size is small in mammals
comparatively because most of its parts become a part of cerebrum (including olfactory tract)
some animals like sharks and dogs have well developed olfactory lobes.
Cerebral hemispheres: Controls and regulates different parts of brain. This is the center of
conscious senses, will power, voluntary movements, knowledge, memory, speech and thinking,
reasoning etc. different sense organs send impulses here, and analysis and coordination of
impulses is done then messages are transferred according to the reactions through voluntary
muscles. All the voluntary actions are controlled by cerebral hemispheres.
Diencephalon: Pineal body, situated in the epithalamus, controls the sexual maturity of animal.
Thalamus – Act as relay center for sensory stimulation. In lower animals, cerebral cortex is
not developed and thalamus acts as sensory center. It is related with RAS and also act as
limbic part.
Functions of hypothalamus: Thermoregulation, behavior and emotion, endocrine control,
biological clock system and ANS control.
Centers of animal feelings/ emotions like sleep, anger, (libido), hate, love, affection, and
temperature control pain, hunger, thirst and satisfaction in the hypothalamus.
Optic chiasma found in the hypothalamus carry optic impulses received from eyes to the
cerebral hemispheres. Animal becomes blind if this part is destroyed by chance.
Metathalamus: It is related with MGB and LGB: MGB is related with hearing and LGB related
with vision. Nerve fibers of concerning place go through metathalamus.
Mid brain: Four optic lobes or colliculus present, superior optic lobes are the main centers of
pupillary light reflexes inferior optic lobes are related with acoustic (sound) reflex action.
Crura cerebri controls the muscles of limbs.
Cerebellum: Impulses are received from different voluntary muscles, joints and controlling
of their movements. When alcohol is consumed in excess, the cerebellum gets affected; as
a result one cannot maintain balance and walking in disturbed.
Thus it is related with fine and skillful voluntary movement and also related with body
balance, equilibrium, posture and tone.
Pons regulates the breathing reaction through pneumotaxic center.
43
Medulla oblongata: Controls all the involuntary activities of the body eg. Heart beats,
respiration, metabolism, secretory actions of different cells rate of engulfing food etc. it acts
as conduction path for all impulses between spinal cord and remaining portions of brain. It is
also concerned with reflex – sneezing reflex, salivation reflex, coughing reflex, swallowing
reflex, vomiting reflex, yawning reflex.
H. Basal nuclei / Basal ganglia: Situated in the wall of cerebral hemisphere. Corpus striatum
(caudate nucleus + (putamen globus pallidus) lentiform nucleus) + amygdaloid + claustrum.
Cleft for internal capsule
Caudate
nucleus
Levels of
sections
above
Lentiform nucleus
(globus pallidus medial
to putamen)
Amygdaloid body Tail of caudate nucleus
Lateral geniculate body
Medial geniculate body
Pulvinar
A
B
Thalamus
Body
Head
A
B
Interrelationship of thalamus, lentiform nucleus, caudate nucleus, and amygdaloid body
Functions:
– Maintains muscle tone.
– Regulates automatic associated movement like swinging of arms during walking.
– In lower animals, when cerebral cortex is not developed basal nuclei acts as motor center.
– Lesion in basal nuclei leads to parkinsonism (rigidity, tremor at rest, mask like face)
– Regulate stereotypic movements; related to initiation and termination of movements.
2.1.2 Spinal cord
A. Anatomy
Medulla oblongata comes out from foramen of magnum and continues in neural canal of
vertebral column, the continued part of MO is known as spinal cord. It extends from base of
skull to lower vertebra of lumbar (L
1
). Its upper part is wide while lower most part is narrow
known as conus medullaris.
Medulla oblongata: Controls all the involuntary activities of the body eg. Heart beats,
respiration, metabolism, secretory actions of different cells rate of engulfing food etc. it acts
as conduction path for all impulses between spinal cord and remaining portions of brain. It is
also concerned with reflex – sneezing reflex, salivation reflex, coughing reflex, swallowing
reflex, vomiting reflex, yawning reflex.
H. Basal nuclei / Basal ganglia: Situated in the wall of cerebral hemisphere. Corpus striatum
(caudate nucleus + (putamen globus pallidus) lentiform nucleus) + amygdaloid + claustrum.
Cleft for internal capsule
Caudate
nucleus
Levels of
sections
above
Lentiform nucleus
(globus pallidus medial
to putamen)
Amygdaloid body Tail of caudate nucleus
Lateral geniculate body
Medial geniculate body
Pulvinar
A
B
Thalamus
Body
Head
A
B
Interrelationship of thalamus, lentiform nucleus, caudate nucleus, and amygdaloid body
Functions:
– Maintains muscle tone.
– Regulates automatic associated movement like swinging of arms during walking.
– In lower animals, when cerebral cortex is not developed basal nuclei acts as motor center.
– Lesion in basal nuclei leads to parkinsonism (rigidity, tremor at rest, mask like face)
– Regulate stereotypic movements; related to initiation and termination of movements.
2.1.2 Spinal cord
A. Anatomy
Medulla oblongata comes out from foramen of magnum and continues in neural canal of
vertebral column, the continued part of MO is known as spinal cord. It extends from base of
skull to lower vertebra of lumbar (L
1
). Its upper part is wide while lower most part is narrow
known as conus medullaris.
44
Conus medullaris is present upto L
1
vertebra.
Terminal part of conus medullaris extends in the
form of thread like structure made up of fibrous
connective tissue called filum terminale.
Filum terminale is non-nervous part.
Metacoel also continues in spinal cord where it
is known as neurocoel or central canal.
Spinal cord is also covered by durameter,
arachnoid and piameter. A narrow space is found
between vertebra and durameter known as
epidural space.
Length of spinal cord is 45 cm, length of filum
terminale is 20 cm and weight of spinal cord is
approximately 35 gm.
B. Internal structure
The outer part of spinal cord is of white matter while inner part is gray matter.
On the dorso lateral and ventro lateral surface of spinal cord, the gray matter (butter fly like)
projects outside and forms the one pair dorsal and ventral horns.
Due to formation of dorsal and ventral horns, white matter is divided into 4 segments and is
known as funiculus or white column.
Dorsal and ventral horns continue in a tube like (bundle of nerve fibers) structure known as
root of dorsal and ventral horn. In root of dorsal horn, ganglia is present called dorsal root
ganglia. Both root are combined with each other at the place of intervertebral foramen.
Vertebra
Medulla
Conus medullaris
Dural sheath
Filum terminale
Coccyx
Level of
lumbar
puncture
C1
L1
L3
L4
S2
Ventral horn
Lateral horn
Transverse section of spinal cord
Dorsal root ganglieDorsal Horn
Interneuron
Anterior median fissure
Motor fibre
Ramus ventralis
Ramus
communicans
(form ANS)
Ramus dorsalis
Intervertebral foramen (IVF)
Sensory nerve fibre
Posterior median septum
Neurocoel
Mixed nerve
Mixed nerve
Grey matter
W hite matter
S
M
Conus medullaris is present upto L
1
vertebra.
Terminal part of conus medullaris extends in the
form of thread like structure made up of fibrous
connective tissue called filum terminale.
Filum terminale is non-nervous part.
Metacoel also continues in spinal cord where it
is known as neurocoel or central canal.
Spinal cord is also covered by durameter,
arachnoid and piameter. A narrow space is found
between vertebra and durameter known as
epidural space.
Length of spinal cord is 45 cm, length of filum
terminale is 20 cm and weight of spinal cord is
approximately 35 gm.
B. Internal structure
The outer part of spinal cord is of white matter while inner part is gray matter.
On the dorso lateral and ventro lateral surface of spinal cord, the gray matter (butter fly like)
projects outside and forms the one pair dorsal and ventral horns.
Due to formation of dorsal and ventral horns, white matter is divided into 4 segments and is
known as funiculus or white column.
Dorsal and ventral horns continue in a tube like (bundle of nerve fibers) structure known as
root of dorsal and ventral horn. In root of dorsal horn, ganglia is present called dorsal root
ganglia. Both root are combined with each other at the place of intervertebral foramen.
Vertebra
Medulla
Conus medullaris
Dural sheath
Filum terminale
Coccyx
Level of
lumbar
puncture
C1
L1
L3
L4
S2
Ventral horn
Lateral horn
Transverse section of spinal cord
Dorsal root ganglieDorsal Horn
Interneuron
Anterior median fissure
Motor fibre
Ramus ventralis
Ramus
communicans
(form ANS)
Ramus dorsalis
Intervertebral foramen (IVF)
Sensory nerve fibre
Posterior median septum
Neurocoel
Mixed nerve
Mixed nerve
Grey matter
W hite matter
S
M
45
Sensory neurons are found in dorsal root ganglia (pseudounipolar) and near to inter vertebral
foramen, its axon extend and gets embedded into gray matter of spinal cord and sensory
nerve fiber come from ganglia and make synapse with ventral root neuron.
Motor neurons are found in the ventral root. Cyton is found in ventral horn while its dendrons
are embedded into gray matter of spinal cord where they make synapse with axon of sensory
neuron.
Axon of motor neuron extends up to intervertebral foramen.
Both sensory and motor nerve fibers combinely come out from intervertebral foramen and
form spinal nerve.
In some part, lateral horns are also found. Lateral horn cells are found in these horns. There
nerve fibers come through ventral root and further come into intervertebral foramen. These
fibers called Ramus communicans. Ramus communicans forms ANS .
The group of spinal nerve at the terminal end (L
1
) of spinal cord from tail like structure called
cauda equina (horse tail).
Spinal nerve and its branches are mixed type except Ramus communicans.
C. Functions:
Acts as bridge between brain and organs of the body.
Provides relay path for the impulses coming from brain.
Regulates and conducts the reflex action.
TARGET POINTS
REFLEX ACTION
“Marshal Hall” first observed the reflex actions.
Reflex actions are spontaneous, automatic and involuntary. These are mechanical responses
produced by specific stimulating receptors.
Reflex actions are completed very quickly as compared to normal actions and have no adverse
effect.
Reflex actions are of two types:
A. Cranial reflex: These actions are completed by brain. No urgency is required for these
actions. These are slow actions e.g. watering of mouth to see good food.
B. Spinal reflex: These actions are completed by spinal cord. Urgency is required for these
actions. These are very fast actions e.g. Displacement of the leg at the time of pinching by
any needle.
Classification of reflex actions on the basis of previous experiences:
Sensory neurons are found in dorsal root ganglia (pseudounipolar) and near to inter vertebral
foramen, its axon extend and gets embedded into gray matter of spinal cord and sensory
nerve fiber come from ganglia and make synapse with ventral root neuron.
Motor neurons are found in the ventral root. Cyton is found in ventral horn while its dendrons
are embedded into gray matter of spinal cord where they make synapse with axon of sensory
neuron.
Axon of motor neuron extends up to intervertebral foramen.
Both sensory and motor nerve fibers combinely come out from intervertebral foramen and
form spinal nerve.
In some part, lateral horns are also found. Lateral horn cells are found in these horns. There
nerve fibers come through ventral root and further come into intervertebral foramen. These
fibers called Ramus communicans. Ramus communicans forms ANS .
The group of spinal nerve at the terminal end (L
1
) of spinal cord from tail like structure called
cauda equina (horse tail).
Spinal nerve and its branches are mixed type except Ramus communicans.
C. Functions:
Acts as bridge between brain and organs of the body.
Provides relay path for the impulses coming from brain.
Regulates and conducts the reflex action.
TARGET POINTS
REFLEX ACTION
“Marshal Hall” first observed the reflex actions.
Reflex actions are spontaneous, automatic and involuntary. These are mechanical responses
produced by specific stimulating receptors.
Reflex actions are completed very quickly as compared to normal actions and have no adverse
effect.
Reflex actions are of two types:
A. Cranial reflex: These actions are completed by brain. No urgency is required for these
actions. These are slow actions e.g. watering of mouth to see good food.
B. Spinal reflex: These actions are completed by spinal cord. Urgency is required for these
actions. These are very fast actions e.g. Displacement of the leg at the time of pinching by
any needle.
Classification of reflex actions on the basis of previous experiences:
46
A. Conditioned reflex: Previous experience is required to complete these actions. E.g.
swimming, cycling, dancing, singing etc. These actions are studied first by Evan Pavlov on
dog. Initially these actions are voluntary at the time of learning and after perfection, these
become involuntary.
B. Unconditioned reflex: These actions do not require previous experience e.g. sneezing,
coughing, yawning, sexual behavior for opposite sex partner, migration in birds etc.
REFLEX ARCH:
The path of completion of reflex action is called reflex arch.
Sensory fibers carry sensory impulses in the gray matter. These sensory impulses are converted
now into motor impulses and reach up to muscles. These muscles show reflex actions for
motor impulses obtained from motor neurons. Reflex arch is of two types:
A. Monosynaptic: There is a direct synapse (relation) found between sensory and motor
neurons, thus nerve impulse travels through only one synapse. E.g. Stretch reflex.
B. Polysynaptic: There are one or more small neurons found in between the sensory and
motor neurons. These small neurons are called connector neuron or inter neurons or
internuncial neurons e.g. withdrawal reflex. Nerve impulse will have to travel through more
than one synapse in this reflex arch.
To brain
6Primary afferent
neuron stimulates
inhibitory interneuron
7Interneuron inhibits
alpha motor neuron
to flexor muscle
5Alpha motor neuron
stimulates extensor
muscle to contract
3Primary afferent neuron excited
4Primary afferent neuron stimulates
alpha motor neuron
to extensor muscle
2Muscle spindle
stimulated
Extensor muscle
stretched
1
Flexor muscle
(antagonist) relaxes
8
Stretch reflex
A. Conditioned reflex: Previous experience is required to complete these actions. E.g.
swimming, cycling, dancing, singing etc. These actions are studied first by Evan Pavlov on
dog. Initially these actions are voluntary at the time of learning and after perfection, these
become involuntary.
B. Unconditioned reflex: These actions do not require previous experience e.g. sneezing,
coughing, yawning, sexual behavior for opposite sex partner, migration in birds etc.
REFLEX ARCH:
The path of completion of reflex action is called reflex arch.
Sensory fibers carry sensory impulses in the gray matter. These sensory impulses are converted
now into motor impulses and reach up to muscles. These muscles show reflex actions for
motor impulses obtained from motor neurons. Reflex arch is of two types:
A. Monosynaptic: There is a direct synapse (relation) found between sensory and motor
neurons, thus nerve impulse travels through only one synapse. E.g. Stretch reflex.
B. Polysynaptic: There are one or more small neurons found in between the sensory and
motor neurons. These small neurons are called connector neuron or inter neurons or
internuncial neurons e.g. withdrawal reflex. Nerve impulse will have to travel through more
than one synapse in this reflex arch.
To brain
6Primary afferent
neuron stimulates
inhibitory interneuron
7Interneuron inhibits
alpha motor neuron
to flexor muscle
5Alpha motor neuron
stimulates extensor
muscle to contract
3Primary afferent neuron excited
4Primary afferent neuron stimulates
alpha motor neuron
to extensor muscle
2Muscle spindle
stimulated
Extensor muscle
stretched
1
Flexor muscle
(antagonist) relaxes
8
Stretch reflex
47
2Sensory neuron
activates multiple
interneurons
3Ipsilateral motor neurons to flexor excited
5Contralateral
motor neurons
to extensor excited
4Ipsilateral
flexor contracts
1Stepping on
glass stimulates
pain receptors in right foot
Withdrawal of right leg (flexor reflex)
Extension of left leg
(crossed extension reflex)
6
Withdrawal reflex
2.2 PERIPHERAL NERVOUS SYSTEM
All the nerves arising from brain and spinal cord are included in peripheral nervous system. Nerves
arising from brain are called cranial nerves, and nerves coming out of spinal cords are called
spinal nerves. 12 pairs of cranial nerves are found in reptiles, birds and mammals but amphibians
and fishes have only 10 pairs of cranial nerves.
In human, I, II, and VIII cranial nerves out of 12 pairs of total cranial nerves are pure sensory in
nature. III, IV, VI, XI, and XII cranial nerves are motor nerves and V, VII, IX and X cranial nerves are
mixed types of nerves. Fibers of autonomous nervous system are found in III, VII, IX and X cranial
nerves.
Knee jerk reflex Withdrawal reflex
No involvement of any interneurons. Role of interneuron is important.
It is an example of monosynaptic reflex. It is an example of polysynaptic reflex.
2Sensory neuron
activates multiple
interneurons
3Ipsilateral motor neurons to flexor excited
5Contralateral
motor neurons
to extensor excited
4Ipsilateral
flexor contracts
1Stepping on
glass stimulates
pain receptors in right foot
Withdrawal of right leg (flexor reflex)
Extension of left leg
(crossed extension reflex)
6
Withdrawal reflex
2.2 PERIPHERAL NERVOUS SYSTEM
All the nerves arising from brain and spinal cord are included in peripheral nervous system. Nerves
arising from brain are called cranial nerves, and nerves coming out of spinal cords are called
spinal nerves. 12 pairs of cranial nerves are found in reptiles, birds and mammals but amphibians
and fishes have only 10 pairs of cranial nerves.
In human, I, II, and VIII cranial nerves out of 12 pairs of total cranial nerves are pure sensory in
nature. III, IV, VI, XI, and XII cranial nerves are motor nerves and V, VII, IX and X cranial nerves are
mixed types of nerves. Fibers of autonomous nervous system are found in III, VII, IX and X cranial
nerves.
Knee jerk reflex Withdrawal reflex
No involvement of any interneurons. Role of interneuron is important.
It is an example of monosynaptic reflex. It is an example of polysynaptic reflex.
48
TARGET POINTS
Longest cranial nerve is vagus nerve.
Largest cranial nerve is trigeminal nerve.
Smallest cranial nerve is abducens cranial nerve.
Thinnest cranial nerve is trochlear/ pathetic.
Trigeminal nerve is also called “ the dentist nerve” because the dentists desensitizes this nerve
with some anesthetic before pulling out the troubling tooth.
Important nuclei related with cranial nerves:
E danger westpal nucleusocculomoto nerve.
Gasserian gangliontrigeminal nerve.
Semilunar ganglion
Nervus intermediumfacial nerve
Geniculate ganglion.
2.2.1 Human cranial nerves
No. Name Origin Distribution Nature Function
I Olfactory Olfactory Enters olfactory lobes. Sensory Smell
epithelium Extends to temporal lobe.
II Optic Retina Leads to occipital lobe. Sensory Sight
III Oculomotor Mid brain Four eye muscles Motor Movement of
eyeball
IV Trochlear Mid brain Superior oblique eye muscle. Motor Movement of
(pathetic) eyeball
V Trigeminal Pons – Mixed
(dentist nerve) –
(i) Opthalmic Skin of nose, upper eyelids, Sensory Sensory supply
forehead, scalp, conjunctiva, to concerning
lachrymal gland. part
(ii) Maxillary – Mucous membrane of cheeks and Sensory –
upper lip and lower eyelid.
(iii) Mandibular – Lower jaw, lower lip, pinna. Mixed Muscle of
Mastication
VI Abducens Pons Lateral rectus eye muscle. Motor Movement of
eyeball
TARGET POINTS
Longest cranial nerve is vagus nerve.
Largest cranial nerve is trigeminal nerve.
Smallest cranial nerve is abducens cranial nerve.
Thinnest cranial nerve is trochlear/ pathetic.
Trigeminal nerve is also called “ the dentist nerve” because the dentists desensitizes this nerve
with some anesthetic before pulling out the troubling tooth.
Important nuclei related with cranial nerves:
E danger westpal nucleusocculomoto nerve.
Gasserian gangliontrigeminal nerve.
Semilunar ganglion
Nervus intermediumfacial nerve
Geniculate ganglion.
2.2.1 Human cranial nerves
No. Name Origin Distribution Nature Function
I Olfactory Olfactory Enters olfactory lobes. Sensory Smell
epithelium Extends to temporal lobe.
II Optic Retina Leads to occipital lobe. Sensory Sight
III Oculomotor Mid brain Four eye muscles Motor Movement of
eyeball
IV Trochlear Mid brain Superior oblique eye muscle. Motor Movement of
(pathetic) eyeball
V Trigeminal Pons – Mixed
(dentist nerve) –
(i) Opthalmic Skin of nose, upper eyelids, Sensory Sensory supply
forehead, scalp, conjunctiva, to concerning
lachrymal gland. part
(ii) Maxillary – Mucous membrane of cheeks and Sensory –
upper lip and lower eyelid.
(iii) Mandibular – Lower jaw, lower lip, pinna. Mixed Muscle of
Mastication
VI Abducens Pons Lateral rectus eye muscle. Motor Movement of
eyeball
49
Olfactory
nerve
Oculomotor
nerve
Trochlear nerve
Abducens
nerve
Vestibulocochlear
nerves
Hypoglossal
nerves
Accessory
nerves
Optic nerve
Cranial nerves
2.2.2 Spinal nerves
In rabbit, there are 37 pairs while in frog there are 9 or 10 pairs. Humans have only 31
pairs of spinal nerves. Caudal spinal nerves are absent because human is a tailless animal
and only 1 pair coccygeal nerve are present.
Each spinal nerve is mixed type and arises from the roots of the horns of gray matter of the
spinal cord.
VII Facial Pons Face, neck, taste buds, salivary Mixed Taste (ant. 2/3
gland. part of tongue)
facial expression,
saliva secretion
VIII Auditory Pons Internal ear Sensory
(i) Cochlear -------- -------- -------- Hearing and
(ii)Vestibular -------- -------- -------- equilibrium
IX Glossopha- Medulla Muscles and mucus
ryngeal membrane of pharyx and tongue. Mixed Taste (post. 1/3
part of tongue),
saliva secretion
X Vagus Medulla Larynx, lungs, heart, stomach, Mixed Visceral
(pneumo- intestine. sensations and
gastric) movements
XI Accessory Medulla Muscles of pharynx, larynx Motor Movement of
spinal pharynx, larynx
XII Hypoglossal Medulla Muscles of tongue Motor Movement of
tongue
Olfactory
nerve
Oculomotor
nerve
Trochlear nerve
Abducens
nerve
Vestibulocochlear
nerves
Hypoglossal
nerves
Accessory
nerves
Optic nerve
Cranial nerves
2.2.2 Spinal nerves
In rabbit, there are 37 pairs while in frog there are 9 or 10 pairs. Humans have only 31
pairs of spinal nerves. Caudal spinal nerves are absent because human is a tailless animal
and only 1 pair coccygeal nerve are present.
Each spinal nerve is mixed type and arises from the roots of the horns of gray matter of the
spinal cord.
VII Facial Pons Face, neck, taste buds, salivary Mixed Taste (ant. 2/3
gland. part of tongue)
facial expression,
saliva secretion
VIII Auditory Pons Internal ear Sensory
(i) Cochlear -------- -------- -------- Hearing and
(ii)Vestibular -------- -------- -------- equilibrium
IX Glossopha- Medulla Muscles and mucus
ryngeal membrane of pharyx and tongue. Mixed Taste (post. 1/3
part of tongue),
saliva secretion
X Vagus Medulla Larynx, lungs, heart, stomach, Mixed Visceral
(pneumo- intestine. sensations and
gastric) movements
XI Accessory Medulla Muscles of pharynx, larynx Motor Movement of
spinal pharynx, larynx
XII Hypoglossal Medulla Muscles of tongue Motor Movement of
tongue
50
In dorsal root only afferent or sensory fibers and in ventral root efferent or motor fibers are
found.
Both the roots after moving for distance in the spinal cord of vertebrates combine with each
other and come out from the inter vertebral foramen in the form of spinal nerves.
As soon as the spinal nerves comes out of the inter vertebral foramen they divide into 3
branches:
Ramus dorsalis
Ramus ventralis
Ramus communicans
Somatic nerve
A.N.S
Sympathetic nervous system
Parasympathetic nervous system
Spinal nerves of rabbit
2.2.3 Autonomic nervous system
The autonomic nervous system is a part of the peripheral nervous system which controls activities
inside the body that are normally involuntary, such as heart beat, peristalsis, sweating etc. It consists
of motor neuron passing to the smooth muscle of internal organs. Smooth muscles are involuntary
muscles. Most of the activities of the autonomic nervous system is controlled within the spinal cord
or brain by reflexes known as visceral reflexes and does not involve the conscious control of higher
centers of the brain.
Overall control of the autonomic nervous system is maintained, however by centers in the medulla
(a part of the hind brain) and hypothalamus. These receive and integrate sensory information and
coordinate this with information from other parts of the nervous system to produce the appropriate
response.
ANS plays an important role in maintaining the constant internal environment (homeostasis). ANS is
composed of two types of neurons, a preganglionic neuron (myelinated) which leaves the central
nervous system in the ventral root before synapsing several postganglionic neurons (non myelinated)
leading to effector (concerning organs).
Cervical spinal nerves 8 Pairs -I To -VIII
Thoracic spinal nerves 12 airs -IX To -XX
Lumbar spinal nerves 7 pairs -XXI To -XXVII
(in human – 21 to 25 (5 pair)]
Sacral spinal nerves 4 pairs -XXVIII To -XXXI
(in human – 26 to 30 (5 pairs)]
Caudal spinal nerves 5 pairs -XXXII To -XXXVII
(in human- 1 pair coccygeal nerve)
In dorsal root only afferent or sensory fibers and in ventral root efferent or motor fibers are
found.
Both the roots after moving for distance in the spinal cord of vertebrates combine with each
other and come out from the inter vertebral foramen in the form of spinal nerves.
As soon as the spinal nerves comes out of the inter vertebral foramen they divide into 3
branches:
Ramus dorsalis
Ramus ventralis
Ramus communicans
Somatic nerve
A.N.S
Sympathetic nervous system
Parasympathetic nervous system
Spinal nerves of rabbit
2.2.3 Autonomic nervous system
The autonomic nervous system is a part of the peripheral nervous system which controls activities
inside the body that are normally involuntary, such as heart beat, peristalsis, sweating etc. It consists
of motor neuron passing to the smooth muscle of internal organs. Smooth muscles are involuntary
muscles. Most of the activities of the autonomic nervous system is controlled within the spinal cord
or brain by reflexes known as visceral reflexes and does not involve the conscious control of higher
centers of the brain.
Overall control of the autonomic nervous system is maintained, however by centers in the medulla
(a part of the hind brain) and hypothalamus. These receive and integrate sensory information and
coordinate this with information from other parts of the nervous system to produce the appropriate
response.
ANS plays an important role in maintaining the constant internal environment (homeostasis). ANS is
composed of two types of neurons, a preganglionic neuron (myelinated) which leaves the central
nervous system in the ventral root before synapsing several postganglionic neurons (non myelinated)
leading to effector (concerning organs).
Cervical spinal nerves 8 Pairs -I To -VIII
Thoracic spinal nerves 12 airs -IX To -XX
Lumbar spinal nerves 7 pairs -XXI To -XXVII
(in human – 21 to 25 (5 pair)]
Sacral spinal nerves 4 pairs -XXVIII To -XXXI
(in human – 26 to 30 (5 pairs)]
Caudal spinal nerves 5 pairs -XXXII To -XXXVII
(in human- 1 pair coccygeal nerve)
51
Mechanism sites of ANS: Involuntary muscles, exocrine glands, blood vessels, skin (pilomotor
muscles, blood vessels, sweat glands).
There are two divisions of ANS: The sympathetic (SNS) and the parasympathetic (PNS) –
A. Sympathetic system is related with such visceral reactions, which increases the protection of
body in adverse atmospheric conditions along with calorie consumption (causes loss of energy).
B. Parasympathetic system is related with those reactions in which energy is conserved.
In this way, autonomic nervous system controls the activities of visceral organs double sided i.e.
antagonistic to each other.
Anatomical difference between SNS and PNS
Physiological difference between SNS and PNS
Sympathetic nervous system Parasympathetic nervous system
Thoracico lumbar outflow (T
1
to L
3
) (Ramus Cranio sacral outflow (cranial nerves) 3, 7, 9,
communicans of T
1
to L
3
) 10 and sacral’s ramus communicans 2, 3, 4.
Just lateral to vertebral column sympathetic Ganglia are situated separately either near the
trunks are there on both sides (each made up organ or surface of organ.
of 22 ganglia) (rabbit = 18 ganglia)
Preganglionic nerve fibers (Ramus communicans Preganglionic nerve fibers are longer than
of spinal nerves) are smaller than post ganglionic postganglionic nerve fibers.
nerve fibers (arises from sympathetic trunk or
ganglia to organs)
Preganglionic nerve fibers are cholinergic Both pre and post ganglionic nerve fibers are
(filled with acetylcholine) and post ganglionic cholinergic.
nerve fibers are adrenergic (filled with
noradrenaline) except sweat gland which have
cholinergic postganglionic nerve fibers.
Preganglionic nerve fibers are made up of white
ramus communicans and postganglionic nerve
fibers are made up of gray ramus communicans.
Visceral organs Sympathetic nervous Parasympathetic nervous
system system
Secretion Acetylcholine + sympathetin Only acetylcholine
Iris of eye Dilates pupils Constricts pupils
Tear glands or Stimulates secretion of lachrymal Inhibits secretion of lachrymal
lachrymal glands glands glands
Mechanism sites of ANS: Involuntary muscles, exocrine glands, blood vessels, skin (pilomotor
muscles, blood vessels, sweat glands).
There are two divisions of ANS: The sympathetic (SNS) and the parasympathetic (PNS) –
A. Sympathetic system is related with such visceral reactions, which increases the protection of
body in adverse atmospheric conditions along with calorie consumption (causes loss of energy).
B. Parasympathetic system is related with those reactions in which energy is conserved.
In this way, autonomic nervous system controls the activities of visceral organs double sided i.e.
antagonistic to each other.
Anatomical difference between SNS and PNS
Physiological difference between SNS and PNS
Sympathetic nervous system Parasympathetic nervous system
Thoracico lumbar outflow (T
1
to L
3
) (Ramus Cranio sacral outflow (cranial nerves) 3, 7, 9,
communicans of T
1
to L
3
) 10 and sacral’s ramus communicans 2, 3, 4.
Just lateral to vertebral column sympathetic Ganglia are situated separately either near the
trunks are there on both sides (each made up organ or surface of organ.
of 22 ganglia) (rabbit = 18 ganglia)
Preganglionic nerve fibers (Ramus communicans Preganglionic nerve fibers are longer than
of spinal nerves) are smaller than post ganglionic postganglionic nerve fibers.
nerve fibers (arises from sympathetic trunk or
ganglia to organs)
Preganglionic nerve fibers are cholinergic Both pre and post ganglionic nerve fibers are
(filled with acetylcholine) and post ganglionic cholinergic.
nerve fibers are adrenergic (filled with
noradrenaline) except sweat gland which have
cholinergic postganglionic nerve fibers.
Preganglionic nerve fibers are made up of white
ramus communicans and postganglionic nerve
fibers are made up of gray ramus communicans.
Visceral organs Sympathetic nervous Parasympathetic nervous
system system
Secretion Acetylcholine + sympathetin Only acetylcholine
Iris of eye Dilates pupils Constricts pupils
Tear glands or Stimulates secretion of lachrymal Inhibits secretion of lachrymal
lachrymal glands glands glands
52
TARGET POINTS
Heart Increases the rate of cardiac Inhibits the rate of cardiac
contraction i.e. accelerates heart beat contraction i.e. retards heart beat
Secretion of adrenal Stimulates adrenal secretion Inhibits adrenal secretion
glands
Salivary secretion Inhibits the secretion of salivary and Stimulates the secretion of
digestive glands. salivary and digestive glands.
Blood vessels Constricts cutaneous blood vessels, Dilates all blood vessels
which causes increased blood pressure decreasing blood pressure.
but dilates blood vessels of brain,
lungs, heart, and striated muscle.
Increases RBC count in blood.
Lungs, trachea and Dilates trachea bronchi and lungs for Constricts these organs during
bronchi easy breathing. normal breathing.
Alimentary canal Inhibits peristalsis of alimentary canal Stimulates peristalsis of
alimentary canal
Digestive glands Inhibits the secretion of these glands Stimulates the secretion of these
glands
Sweat glands Stimulates secretion of sweat Inhibits secretion of sweat
Arrector pilli Stimulates contraction of these muscles Relaxes arrector pilli muscles
muscles of skin, causing goose flesh
Urinary bladder Relaxes the muscles of urinary bladder Contracts the muscles for
ejaculation of urine (micturition).
Anal sphincter Closes anus by contracting anal Relaxes anal sphincter and opens
sphincters the anus (defecation)
External ganglia Ejaculation Erection
Basal metabolic rate Accelerates BMR Retards BMR.
Comparative account of nervous system in rabbit and human
Characters Rabbit Human
Olfactory lobe
Position Attached distinctly to anterior Attached indistinctly as part of cerebral
end of cerebrum hemisphere embedded in frontal lobe
Shape and size Small, elongated Small, occur as olfactory bulb
Rhinocoel Present Absent and solid lobe
TARGET POINTS
Heart Increases the rate of cardiac Inhibits the rate of cardiac
contraction i.e. accelerates heart beat contraction i.e. retards heart beat
Secretion of adrenal Stimulates adrenal secretion Inhibits adrenal secretion
glands
Salivary secretion Inhibits the secretion of salivary and Stimulates the secretion of
digestive glands. salivary and digestive glands.
Blood vessels Constricts cutaneous blood vessels, Dilates all blood vessels
which causes increased blood pressure decreasing blood pressure.
but dilates blood vessels of brain,
lungs, heart, and striated muscle.
Increases RBC count in blood.
Lungs, trachea and Dilates trachea bronchi and lungs for Constricts these organs during
bronchi easy breathing. normal breathing.
Alimentary canal Inhibits peristalsis of alimentary canal Stimulates peristalsis of
alimentary canal
Digestive glands Inhibits the secretion of these glands Stimulates the secretion of these
glands
Sweat glands Stimulates secretion of sweat Inhibits secretion of sweat
Arrector pilli Stimulates contraction of these muscles Relaxes arrector pilli muscles
muscles of skin, causing goose flesh
Urinary bladder Relaxes the muscles of urinary bladder Contracts the muscles for
ejaculation of urine (micturition).
Anal sphincter Closes anus by contracting anal Relaxes anal sphincter and opens
sphincters the anus (defecation)
External ganglia Ejaculation Erection
Basal metabolic rate Accelerates BMR Retards BMR.
Comparative account of nervous system in rabbit and human
Characters Rabbit Human
Olfactory lobe
Position Attached distinctly to anterior Attached indistinctly as part of cerebral
end of cerebrum hemisphere embedded in frontal lobe
Shape and size Small, elongated Small, occur as olfactory bulb
Rhinocoel Present Absent and solid lobe
53
In rabbit, “Swammerdams glands” are absent. These glands are present at the origin place
of spinal nerves in vertebrates and present in frog. It provides extra supply of Ca
++
for synaptic
transmission.
In embryonal: stages inside the brain the layer of gray matter is towards inside and that of white
matter is towards outside. In adults, this arrangement continues in the spinal cord but during
the development of the wall of the brain the gray matter is transferred outside.
In 1 minute 750 ml of blood is conducted to the human brain.
Largest cranial venous sinus is cavernous venous sinus which is situated in the middle
cranial fossa.
All preganglionic sympathetic nerve fibers are myelinated while post ganglionic nerve fiber are
non myelinated.
Alzheimer’s disease: In this disease, the cerebral cortex is atrophied and ultimately the ventricle
enlarges. Symptoms consists loss of memory particularly recent memory. Alzheimer disease is
more common in Down syndrome.
Treatment – no effective treatment.
Stroke – may be caused by hemorrhage into the brain.
Symptoms – unconsciousness.
Treatment – Intravenous tissue plasminogen activator.
Epilepsy – Epilepsy is characterized by short, recurrent periodic attack of motor, sensory of
physiological malfunction.
Cause – Due to abnormal discharge of cerebral neurons.
Cerebrum Surface bears fissures and divided Surface is folded having gyri and sulci,
into lobes. bearing fissures and divided into lobes.
Pallium Developed Highly developed
Corpora striata Comparatively less developed Developed
Pituitary body Infundibulum and hypophysis from Same as in rabbit but intermediate lobe
pituitary body also having an vestigial.
intermediate lobe.
Cerebellum
Divisions Divided into 5 lobes- a median Divided into two cerebellar hemispheres,
vermis, two lateral lobes each connected by median vermis, cerebellar
terminating into a flocculus. peduncle also present
Spinal nerve 37 pairs – 8 cervical, 12 thoracic, 31 pairs- 8 cervical, 12 thoracic,
7 lumbar, 4 sacral and 6 caudal or 5 lumbar, 5 sacral, and 1 coccygeal pairs.
coccygeal pairs
In rabbit, “Swammerdams glands” are absent. These glands are present at the origin place
of spinal nerves in vertebrates and present in frog. It provides extra supply of Ca
++
for synaptic
transmission.
In embryonal: stages inside the brain the layer of gray matter is towards inside and that of white
matter is towards outside. In adults, this arrangement continues in the spinal cord but during
the development of the wall of the brain the gray matter is transferred outside.
In 1 minute 750 ml of blood is conducted to the human brain.
Largest cranial venous sinus is cavernous venous sinus which is situated in the middle
cranial fossa.
All preganglionic sympathetic nerve fibers are myelinated while post ganglionic nerve fiber are
non myelinated.
Alzheimer’s disease: In this disease, the cerebral cortex is atrophied and ultimately the ventricle
enlarges. Symptoms consists loss of memory particularly recent memory. Alzheimer disease is
more common in Down syndrome.
Treatment – no effective treatment.
Stroke – may be caused by hemorrhage into the brain.
Symptoms – unconsciousness.
Treatment – Intravenous tissue plasminogen activator.
Epilepsy – Epilepsy is characterized by short, recurrent periodic attack of motor, sensory of
physiological malfunction.
Cause – Due to abnormal discharge of cerebral neurons.
Cerebrum Surface bears fissures and divided Surface is folded having gyri and sulci,
into lobes. bearing fissures and divided into lobes.
Pallium Developed Highly developed
Corpora striata Comparatively less developed Developed
Pituitary body Infundibulum and hypophysis from Same as in rabbit but intermediate lobe
pituitary body also having an vestigial.
intermediate lobe.
Cerebellum
Divisions Divided into 5 lobes- a median Divided into two cerebellar hemispheres,
vermis, two lateral lobes each connected by median vermis, cerebellar
terminating into a flocculus. peduncle also present
Spinal nerve 37 pairs – 8 cervical, 12 thoracic, 31 pairs- 8 cervical, 12 thoracic,
7 lumbar, 4 sacral and 6 caudal or 5 lumbar, 5 sacral, and 1 coccygeal pairs.
coccygeal pairs
54
Symptoms – Seizures, unconsciousness, involuntary contraction of muscles.
Treatment – Anti epileptic drugs.
Botulism: It is food poisoning disease and it produces by Clostridium botulinum bacteria. This
bacteria release neurotoxin.
Phrenic nerve is branch of cervical plexus which supply diaphragm.
Malathione: This substance is used as insecticide and it destroy the acetyl cholinesterase in
synapse area.
Corpus striatum regulates planning and execution or stereotyped movement.
The region between the thalamus and spinal cord is referred to as brain stem.
Intelligency quoutient (I.Q)
Mental age
= × 100
chrono logical age
Idiot 0-24%
Imbecile 25-49% Moron 50-69%
Borderline 70-79% Low normal 80-89%
Normal 90-109%
Superior 110-119% Very superior 120-139%
Genius 140-More
Symptoms – Seizures, unconsciousness, involuntary contraction of muscles.
Treatment – Anti epileptic drugs.
Botulism: It is food poisoning disease and it produces by Clostridium botulinum bacteria. This
bacteria release neurotoxin.
Phrenic nerve is branch of cervical plexus which supply diaphragm.
Malathione: This substance is used as insecticide and it destroy the acetyl cholinesterase in
synapse area.
Corpus striatum regulates planning and execution or stereotyped movement.
The region between the thalamus and spinal cord is referred to as brain stem.
Intelligency quoutient (I.Q)
Mental age
= × 100
chrono logical age
Idiot 0-24%
Imbecile 25-49% Moron 50-69%
Borderline 70-79% Low normal 80-89%
Normal 90-109%
Superior 110-119% Very superior 120-139%
Genius 140-More
55
1. Which has H shaped gray matter?
a) Cerebrum b) Spinal cord
c) Cerebellum d) Medulla oblongata
2. Match the following human spinal nerves in
column I with II and choose the correct
options
a) A = 2, B = 4, C = 1, D = 3
b) A = 4, B = 3, C = 1, D = 2
c) A = 4, B = 2, C = 1, D = 4
d) A = 1, B = 4, C = 2, D = 3
3. Broca’s area is located in
a) Ventral part of temporal lobe
b) Lateral part of frontal lobe
c) Dorsal part of optic lobe
d) None of them
4. The main function of sympathetic nervous
system are
a) Contraction of skin blood vessels and
sudden increase of blood pressure
b) Contraction of muscles, secretion of
sweat glands and rapid coagulation of
blood
c) Dilation of bronchi, contraction of heart
and sudden decrease in the number of
RBC in the blood
d) All of the above
5. Cavity in spinal cord is called
a) Enterocoel b) Blastocoel
c) Schizocoel d) Neurocoel
Simple Questions
Column I Column II
A. Cervical nerves 1. 5 pairs
B. Thoracic nerves 2. 1 pairs
C. Lumbar nerves 3. 12 pairs
D. Coccygeal nerves 4. 8 pairs
6. Parasympathetic system increase activity of
a) Lacrimal gland, sweat gland, arrector pili
b) Heart, lacrimal gland, pancreas
c) Heart, adrenal gland and sweat gland
d) Gut, iris and urinary bladder
7. Which of the following is responsible for
control of reflex actions?
a) Motor nerves
b) Sensory nerves
c) Central nervous system
d) Sympathetic nervous system
8. Which of the following spinal nerves are not
found in human?
a) Caudal nerves b) Sacral nerves
c) Cervical nerves d) Lumbar nerves
9. Glands of swammerdams are associated
with
a) Nervous system b) Muscles
c) Bones d) All
10. In human, autonomic nervous system is
composed of
a) Sympathetic and parasympathetic
nerves
b) Cranial and spinal nerves
c) Brain and spinal nerves
d) Medullated and non medullated nerves
11. How many pairs of cranial nerves are purely
sensory?
a) Two b) Three
c) Four d) Five
12. If cerebral hemispheres of rabbit are
removed, then it will
a) Die immediately
b) Die after some time
c) Behave normally
d) Stop feeding
1. Which has H shaped gray matter?
a) Cerebrum b) Spinal cord
c) Cerebellum d) Medulla oblongata
2. Match the following human spinal nerves in
column I with II and choose the correct
options
a) A = 2, B = 4, C = 1, D = 3
b) A = 4, B = 3, C = 1, D = 2
c) A = 4, B = 2, C = 1, D = 4
d) A = 1, B = 4, C = 2, D = 3
3. Broca’s area is located in
a) Ventral part of temporal lobe
b) Lateral part of frontal lobe
c) Dorsal part of optic lobe
d) None of them
4. The main function of sympathetic nervous
system are
a) Contraction of skin blood vessels and
sudden increase of blood pressure
b) Contraction of muscles, secretion of
sweat glands and rapid coagulation of
blood
c) Dilation of bronchi, contraction of heart
and sudden decrease in the number of
RBC in the blood
d) All of the above
5. Cavity in spinal cord is called
a) Enterocoel b) Blastocoel
c) Schizocoel d) Neurocoel
Simple Questions
Column I Column II
A. Cervical nerves 1. 5 pairs
B. Thoracic nerves 2. 1 pairs
C. Lumbar nerves 3. 12 pairs
D. Coccygeal nerves 4. 8 pairs
6. Parasympathetic system increase activity of
a) Lacrimal gland, sweat gland, arrector pili
b) Heart, lacrimal gland, pancreas
c) Heart, adrenal gland and sweat gland
d) Gut, iris and urinary bladder
7. Which of the following is responsible for
control of reflex actions?
a) Motor nerves
b) Sensory nerves
c) Central nervous system
d) Sympathetic nervous system
8. Which of the following spinal nerves are not
found in human?
a) Caudal nerves b) Sacral nerves
c) Cervical nerves d) Lumbar nerves
9. Glands of swammerdams are associated
with
a) Nervous system b) Muscles
c) Bones d) All
10. In human, autonomic nervous system is
composed of
a) Sympathetic and parasympathetic
nerves
b) Cranial and spinal nerves
c) Brain and spinal nerves
d) Medullated and non medullated nerves
11. How many pairs of cranial nerves are purely
sensory?
a) Two b) Three
c) Four d) Five
12. If cerebral hemispheres of rabbit are
removed, then it will
a) Die immediately
b) Die after some time
c) Behave normally
d) Stop feeding
56
13. Find out the correct sequence of a simple
reflex arc
a) Brain – spinal cord – nerves – effector.
b) Effector – CNS – sensory nerves –
receptor
c) Muscles – Spinal cord – brain – receptor.
d) Receptor – sensory nerves – CNS –
effector
14. The correct route of reflex arc is
a) Effectors, grey matter, motor fibers,
sensory fibers and receptors
b) Receptors, sensory fibers, grey matter
and motor fibers
c) Receptors, sensory fibers, grey matter,
motor fibers and effectors
d) Sensory fibers, grey matter, motor fibers,
receptors and effectors
15. II, VII, VIII and IX cranial nerves are
a) Optic, facial, auditory, glossopharyngeal
b) Optic, auditory, facial, hypoglossal
c) Occulomotor, auditory, abducens,
hypoglossal
d) Optic, f acial, abducens and
glossopharyngeal
16. Voluntary activities of body are controlled
by
a) Diencephalon b) Cerebrum
c) Crura cerebri d) Cerebellum
17. Which destroys the acetylcholinesterase?
a) Malathione b) CO
c) KCN d) Colchicine
18. Nerve cells possess
1) Dendrites 2) Axon
3) Sarcolemma 4) Neurilemma
a) 1, 2 b) 1, 2, 3
c) 1, 2, 4 d) 1, 2, 3, 4
19. Corpora quadrigemina acts as the center
for
a) Audio and vision
b) Olfaction and gustation
c) Thermoregulation and chemical sense
d) None of the above
20. Brain of rabbit differs from that of frog in
having
a) Large olfactory lobe
b) Small hypothalamus
c) Small cerebellum
d) Corpus callosum
21. Norepinephrine leads to increase in
a) Blood pressure
b) Urine production
c) Cellular respiration
d) Release of epinephrine
22. Posterior choroid plexus in brain is found in
the
a) Diencephalon
b) Cerebrum
c) Cerebellum
d) Space between pons and medulla
(anteriorly) and cerebellum (posteriorly)
23. Which of the following is a richly vascular
layer with lots of blood capillaries
a) Durameter
b) Piameter
c) Epidermis of skin
d) Both (a) and (b)
24. Cerebrospinal fluid is secreted by
a) Cerebellum b) Choroid plexus
c) Olfactory lobe d) Cerebrum
25. Smallest cranial nerve is
a) X cranial nerve b) VI cranial nerve
c) VII cranial nerve d) II cranial nerve
13. Find out the correct sequence of a simple
reflex arc
a) Brain – spinal cord – nerves – effector.
b) Effector – CNS – sensory nerves –
receptor
c) Muscles – Spinal cord – brain – receptor.
d) Receptor – sensory nerves – CNS –
effector
14. The correct route of reflex arc is
a) Effectors, grey matter, motor fibers,
sensory fibers and receptors
b) Receptors, sensory fibers, grey matter
and motor fibers
c) Receptors, sensory fibers, grey matter,
motor fibers and effectors
d) Sensory fibers, grey matter, motor fibers,
receptors and effectors
15. II, VII, VIII and IX cranial nerves are
a) Optic, facial, auditory, glossopharyngeal
b) Optic, auditory, facial, hypoglossal
c) Occulomotor, auditory, abducens,
hypoglossal
d) Optic, f acial, abducens and
glossopharyngeal
16. Voluntary activities of body are controlled
by
a) Diencephalon b) Cerebrum
c) Crura cerebri d) Cerebellum
17. Which destroys the acetylcholinesterase?
a) Malathione b) CO
c) KCN d) Colchicine
18. Nerve cells possess
1) Dendrites 2) Axon
3) Sarcolemma 4) Neurilemma
a) 1, 2 b) 1, 2, 3
c) 1, 2, 4 d) 1, 2, 3, 4
19. Corpora quadrigemina acts as the center
for
a) Audio and vision
b) Olfaction and gustation
c) Thermoregulation and chemical sense
d) None of the above
20. Brain of rabbit differs from that of frog in
having
a) Large olfactory lobe
b) Small hypothalamus
c) Small cerebellum
d) Corpus callosum
21. Norepinephrine leads to increase in
a) Blood pressure
b) Urine production
c) Cellular respiration
d) Release of epinephrine
22. Posterior choroid plexus in brain is found in
the
a) Diencephalon
b) Cerebrum
c) Cerebellum
d) Space between pons and medulla
(anteriorly) and cerebellum (posteriorly)
23. Which of the following is a richly vascular
layer with lots of blood capillaries
a) Durameter
b) Piameter
c) Epidermis of skin
d) Both (a) and (b)
24. Cerebrospinal fluid is secreted by
a) Cerebellum b) Choroid plexus
c) Olfactory lobe d) Cerebrum
25. Smallest cranial nerve is
a) X cranial nerve b) VI cranial nerve
c) VII cranial nerve d) II cranial nerve
57
26. When the medulla oblongata (M.O) is
compressed. Then what happens?
a) Immediately die
b) Die after few hours
c) Live at 1 hour and after it may die
d) No affect
27. Which is correct about Pons varolli?
a) Situated between midbrain and M.O.
b) Pons regulates pneumotaxic center
c) Inner gray, outer white matter
d) All of the above
28. Father of conditioned reflex is
a) Pavlov b) Calvin
c) Oparin d) Smith and Neil
29. Small, solid and four optic lobes or colliculus
called corpora quadrigemia are found in
a) Mammals b) Amphibians
c) Aves d) Reptiles
30. “Foramen of monro” is an aperture found
between
a) Third ventricle and forth ventricle
b) Diocoel and metacoel
c) Brain and spinal cord
d) Lateral ventricle and third ventricle
31. In brain of crura cerebri is a structure made
of
a) Six bands of nerve fibers
b) Eight bands of nerve fibers
c) Two large bands of nerve fibers
d) Four bands of nerve fibers
32. The roof of cerebrum is
a) Centrocoel b) Pallium
c) Arbor vitae d) Third ventricles
1. Regarding cerebrospinal fluid, which of the
following is a false statement?
a) It has a specific gravity of 1.007 and
buoys the brain
b) It maintains a volume of 140 to 200 ml
and a fluid pressure of 10 mm Hg
c) It moves metabolic wastes away from
the cells of nervous tissue
d) It is produced in the choroid plexuses
and drains into the cerebral arterial circle
2. The presence of theta waves in an adult is
an indication of
a) Visual acuity
b) Dreaming
c) Brain damage
d) Severe emotional stress
Difficult Questions
3. A patient scheduled “for surgery confides
in his nurse the night” before that he is
“terribly scared”. Which of the following
indicate(s) increased sympathetic activity in
this patient?
a) Patient complains that his mouth feels
dry
b) Patient’s gown is moist with perspiration
c) Patients appear pale
d) All of the above
4. In a patient with a contusion over the parotid
region, the facial muscles on one side of
the face are paralysed, one eye cannot be
shut and the corner of the mouth droops.
Which cranial nerve is damaged?
a) Abducens nerve
b) Facial nerve
c) Glossopharyngeal nerve
d) Accessory nerve
26. When the medulla oblongata (M.O) is
compressed. Then what happens?
a) Immediately die
b) Die after few hours
c) Live at 1 hour and after it may die
d) No affect
27. Which is correct about Pons varolli?
a) Situated between midbrain and M.O.
b) Pons regulates pneumotaxic center
c) Inner gray, outer white matter
d) All of the above
28. Father of conditioned reflex is
a) Pavlov b) Calvin
c) Oparin d) Smith and Neil
29. Small, solid and four optic lobes or colliculus
called corpora quadrigemia are found in
a) Mammals b) Amphibians
c) Aves d) Reptiles
30. “Foramen of monro” is an aperture found
between
a) Third ventricle and forth ventricle
b) Diocoel and metacoel
c) Brain and spinal cord
d) Lateral ventricle and third ventricle
31. In brain of crura cerebri is a structure made
of
a) Six bands of nerve fibers
b) Eight bands of nerve fibers
c) Two large bands of nerve fibers
d) Four bands of nerve fibers
32. The roof of cerebrum is
a) Centrocoel b) Pallium
c) Arbor vitae d) Third ventricles
1. Regarding cerebrospinal fluid, which of the
following is a false statement?
a) It has a specific gravity of 1.007 and
buoys the brain
b) It maintains a volume of 140 to 200 ml
and a fluid pressure of 10 mm Hg
c) It moves metabolic wastes away from
the cells of nervous tissue
d) It is produced in the choroid plexuses
and drains into the cerebral arterial circle
2. The presence of theta waves in an adult is
an indication of
a) Visual acuity
b) Dreaming
c) Brain damage
d) Severe emotional stress
Difficult Questions
3. A patient scheduled “for surgery confides
in his nurse the night” before that he is
“terribly scared”. Which of the following
indicate(s) increased sympathetic activity in
this patient?
a) Patient complains that his mouth feels
dry
b) Patient’s gown is moist with perspiration
c) Patients appear pale
d) All of the above
4. In a patient with a contusion over the parotid
region, the facial muscles on one side of
the face are paralysed, one eye cannot be
shut and the corner of the mouth droops.
Which cranial nerve is damaged?
a) Abducens nerve
b) Facial nerve
c) Glossopharyngeal nerve
d) Accessory nerve
58
5. Ventral root of spinal nerve has
a) Sensory fibers
b) Motor fibers
c) Sensory and motor fibers both
d) None of these
6. Difference found between brain of frog and
rabbit is
a) Presence of corpus callosum
b) Corpus albicans
c) Four optic lobes
d) All of these
7. Comprehension of spoken and written
words take place in the region of
a) Association area
b) Motor area
c) Wernicke’s area
d) Broca’s area
8. Which converts short time memory into long
time remembrance?
a) Reticular system
b) Hippocampus
c) Thalamus
d) Medulla oblongata
9. Regarding the medulla oblongata, which of
the following is false statement?
a) It is pyramidal in shape
b) It is located within the mesencephalon
c) It contains posterior choroid plexuses
d) It functions as cardiac, vasomotor and
respiratory centers
10. Closing of magandii foramen will prevent
the flow of cerebro spinal fluid from IV
ventricle to
a) Central canal
b) II ventricle
c) III ventricle
d) Outside the brain
11. Which of the following structures is present
characteristically only in mammalian brain?
a) Corpus fibrosum
b) Corpus callosum
c) Corpus luteum
d) Corpus striatum
12. The cavity of diocoel is known as
a) I ventricle
b) II ventricle
c) III ventricle
d) Iter
13. Cell bodies of neurons bringing afferent
information into the spinal cord are located
in
a) Grey matter of spinal cord
b) White matter of spinal cord
c) Dorsal root ganglia
d) Ventral root ganglia
14. How many laminae are present in the grey
matter of spinal cord?
a) Four b) Six
c) Eight d) Ten
15. Hypothalamus does not control
a) Libido
b) Thermoregulation
c) Osmoregulation
d) Hunger and satiety
16. Choroid plexus is a network of
a) Nerves b) Muscle fibers
c) Capillaries d) Lymph vessels
17. Paralysis of both lower limbs due to spinal
cord damage and not the upper limbs is
called
a) Hemiplegia b) Quadriplegia
c) Posterioplegia d) Paraplegia
5. Ventral root of spinal nerve has
a) Sensory fibers
b) Motor fibers
c) Sensory and motor fibers both
d) None of these
6. Difference found between brain of frog and
rabbit is
a) Presence of corpus callosum
b) Corpus albicans
c) Four optic lobes
d) All of these
7. Comprehension of spoken and written
words take place in the region of
a) Association area
b) Motor area
c) Wernicke’s area
d) Broca’s area
8. Which converts short time memory into long
time remembrance?
a) Reticular system
b) Hippocampus
c) Thalamus
d) Medulla oblongata
9. Regarding the medulla oblongata, which of
the following is false statement?
a) It is pyramidal in shape
b) It is located within the mesencephalon
c) It contains posterior choroid plexuses
d) It functions as cardiac, vasomotor and
respiratory centers
10. Closing of magandii foramen will prevent
the flow of cerebro spinal fluid from IV
ventricle to
a) Central canal
b) II ventricle
c) III ventricle
d) Outside the brain
11. Which of the following structures is present
characteristically only in mammalian brain?
a) Corpus fibrosum
b) Corpus callosum
c) Corpus luteum
d) Corpus striatum
12. The cavity of diocoel is known as
a) I ventricle
b) II ventricle
c) III ventricle
d) Iter
13. Cell bodies of neurons bringing afferent
information into the spinal cord are located
in
a) Grey matter of spinal cord
b) White matter of spinal cord
c) Dorsal root ganglia
d) Ventral root ganglia
14. How many laminae are present in the grey
matter of spinal cord?
a) Four b) Six
c) Eight d) Ten
15. Hypothalamus does not control
a) Libido
b) Thermoregulation
c) Osmoregulation
d) Hunger and satiety
16. Choroid plexus is a network of
a) Nerves b) Muscle fibers
c) Capillaries d) Lymph vessels
17. Paralysis of both lower limbs due to spinal
cord damage and not the upper limbs is
called
a) Hemiplegia b) Quadriplegia
c) Posterioplegia d) Paraplegia
59
18. Consider the following statements about the
sympathetic division of the ANS
I) All its neurons release norepinephrine
as their primary neurotransmitter
substance
II) All the cell bodies of its post ganglionic
neurons lie in or near the organ
innervated
III) The cell bodies of its pre ganglionic
neurons lie in the thoracic and lumbar
spinal cord
Of these statements
a) I is true
b) II is true
c) III is true
d) I and II are true
19. A patient with symptoms of tremor, halting
speech and an irregular gait may have
experienced trauma to the
a) Cerebrum b) Pons
c) Cerebellum d) Thalamus
20. Parkinson’s disease is present due to lesion
in
a) Corpus striatum
b) RAS
c) Limbic system
d) Analysis center of cerebrum
21. The name of nervous band connecting the
cerebral hemispheres in rabbit is
a) Corpus albicans
b) Corpus callosum
c) Corpus striatum
d) Corpus spongiosum
22. Which one of the following menix is present
only in mammalian brain?
a) Durameter b) Arachnoid
c) Piameter d) None of them
23. Which statement is wrong about the function
of brain?
a) Hypothalamus mainly controls ANS
b) Voluntary muscle activity is started by
cerebellum
c) Medulla oblongata regulates involuntary
activity of our body
d) Thalamus is responsible for sensory
sensation in lower vertebrate
24. The “butter fly” like structure surrounding
the central of human’s spinal cord is called
a) Funiculus b) Horn
c) White matter d) Gray matter
25. Brain waves common to a healthy sleeping
person and a brain damaged awake person
are called
a) Alpha waves
b) Beta waves
c) Gamma waves
d) Delta waves
26. The mesencephalic (cerebral) aqueduct
links the
a) Lateral ventricles
b) Lateral ventricles and the third ventricle
c) Third and fourth ventricle
d) Lateral ventricles and the fourth ventricle
27. Two extra cranial nerves found in rabbit/
human are
a) Hypoglossal and spinal accessory
b) Hypoglossal and pneumatogastric
c) Spinal accessory and glossopharyngeal
d) Hypoglossal and glossopharyngeal
28. The corpora quadrigemina, composed of
the superior and inferior colliculi, is located
in the
a) Telencephalon b) Mesencephalon
c) Diencephalon d) Metencephalon
18. Consider the following statements about the
sympathetic division of the ANS
I) All its neurons release norepinephrine
as their primary neurotransmitter
substance
II) All the cell bodies of its post ganglionic
neurons lie in or near the organ
innervated
III) The cell bodies of its pre ganglionic
neurons lie in the thoracic and lumbar
spinal cord
Of these statements
a) I is true
b) II is true
c) III is true
d) I and II are true
19. A patient with symptoms of tremor, halting
speech and an irregular gait may have
experienced trauma to the
a) Cerebrum b) Pons
c) Cerebellum d) Thalamus
20. Parkinson’s disease is present due to lesion
in
a) Corpus striatum
b) RAS
c) Limbic system
d) Analysis center of cerebrum
21. The name of nervous band connecting the
cerebral hemispheres in rabbit is
a) Corpus albicans
b) Corpus callosum
c) Corpus striatum
d) Corpus spongiosum
22. Which one of the following menix is present
only in mammalian brain?
a) Durameter b) Arachnoid
c) Piameter d) None of them
23. Which statement is wrong about the function
of brain?
a) Hypothalamus mainly controls ANS
b) Voluntary muscle activity is started by
cerebellum
c) Medulla oblongata regulates involuntary
activity of our body
d) Thalamus is responsible for sensory
sensation in lower vertebrate
24. The “butter fly” like structure surrounding
the central of human’s spinal cord is called
a) Funiculus b) Horn
c) White matter d) Gray matter
25. Brain waves common to a healthy sleeping
person and a brain damaged awake person
are called
a) Alpha waves
b) Beta waves
c) Gamma waves
d) Delta waves
26. The mesencephalic (cerebral) aqueduct
links the
a) Lateral ventricles
b) Lateral ventricles and the third ventricle
c) Third and fourth ventricle
d) Lateral ventricles and the fourth ventricle
27. Two extra cranial nerves found in rabbit/
human are
a) Hypoglossal and spinal accessory
b) Hypoglossal and pneumatogastric
c) Spinal accessory and glossopharyngeal
d) Hypoglossal and glossopharyngeal
28. The corpora quadrigemina, composed of
the superior and inferior colliculi, is located
in the
a) Telencephalon b) Mesencephalon
c) Diencephalon d) Metencephalon
60
29. The III, VI and XI cranial nerve in mammals
are respectively
a) Occulomotor, abducens and hypoglossal
b) Occulomotor, abducens and spinal
accessory
c) Trochlear, facial and spinal accessory
d) Trigeminal, abducens and vagus
30. Vagus nerve is a
a) Mixed X
th
spinal nerve
b) Mixed XI
th
cranial nerve
c) Mixed X
th
thoracic nerve
d) Mixed X
th
cranial nerve
ANSWER KEYS
Simple Questions
1.b 2.b 3.b 4.d 5.d 6.d 7.c 8.a 9.a 10.a 11.b 12.b
13.d 14.c 15.a 16.b 17.a 18.c 19.a 20.d 21.a 22.d 23.b 24.b
25.b 26.a 27.d 28.a 29.a 30.d 31.c 32.b
Difficult Questions
1.b 2.d 3.d 4.b 5.b 6.d 7.c 8.c 9.b 10.d 11.b 12.c
13.c 14.d 15.a 16.c 17.c 18.c 19.c 20.a 21.b 22.b 23.b 24.d
25.d 26.c 27.a 28.b 29.b 30.d
29. The III, VI and XI cranial nerve in mammals
are respectively
a) Occulomotor, abducens and hypoglossal
b) Occulomotor, abducens and spinal
accessory
c) Trochlear, facial and spinal accessory
d) Trigeminal, abducens and vagus
30. Vagus nerve is a
a) Mixed X
th
spinal nerve
b) Mixed XI
th
cranial nerve
c) Mixed X
th
thoracic nerve
d) Mixed X
th
cranial nerve
ANSWER KEYS
Simple Questions
1.b 2.b 3.b 4.d 5.d 6.d 7.c 8.a 9.a 10.a 11.b 12.b
13.d 14.c 15.a 16.b 17.a 18.c 19.a 20.d 21.a 22.d 23.b 24.b
25.b 26.a 27.d 28.a 29.a 30.d 31.c 32.b
Difficult Questions
1.b 2.d 3.d 4.b 5.b 6.d 7.c 8.c 9.b 10.d 11.b 12.c
13.c 14.d 15.a 16.c 17.c 18.c 19.c 20.a 21.b 22.b 23.b 24.d
25.d 26.c 27.a 28.b 29.b 30.d
61
1. Which of the following answer shows the
correct arrangement of nerve fiber?
CNS
A B
C D
E Sym. Nervous system
a) (A) Centrifugal (B) Efferent (C) PNS (D)
ANS (E) Parasympathetic
b) (A) Centripetal (B) Afferent (C) PNS (D)
ANS (E) Parasympathetic
c) (A) Centrifugal (B) Afferent (C) SNS (D)
ANS (E) Parasympathetic
d) (A) Centripetal (B) Efferent (C) SNS (D)
ANS (E) Parasympathetic
2. The cerebrospinal fluid passes out from the
ventricle of medulla oblongata into the
space between meninges of brain through
a) Foramen of monro
b) Foramen of magnum
c) Foramen of magandii and luschaka
d) Foramen ovale
3. If cerebellum of man gets damaged, his
movement becomes
a) Shaky and speech becomes defective
b) Unbalanced, walk uncontrolled,
defective speech and intention tremor
c) Jerky and defective speech
d) Jerky and walk uncontrolled
4. Phrenic nerve is a
a) Cranial nerve b) Spinal nerve
c) Sciatic nerve d) Lumbar nerve
DPP - 2
5. The diagram shows a section through the
head showing the brain and part of the
spinal cord
Y
X
W
Z
Which structures carry out the functions
listed below?
Conscious Control of body
thought movements
and memory and posture
a) X W
b) W X
c) Y Z
d) Z Y
6. Excessive stimulation of vagus nerve in
humans may lead to
a) Hoarse voice
b) Peptic ulcers
c) Efficient digestion of proteins
d) Irregular contractions of diaphragm
7. Hippocampal lobes are the parts of
a) Olfactory lobes
b) Cerebrum
c) Cerebellum
d) Medulla oblongata
8. If Broca’s area is injured then what happens
firstly
a) Concerning speech muscles are
paralyzed
b) Speech stattered and not clear
c) Unable to speak
d) Only able to speak written word
1. Which of the following answer shows the
correct arrangement of nerve fiber?
CNS
A B
C D
E Sym. Nervous system
a) (A) Centrifugal (B) Efferent (C) PNS (D)
ANS (E) Parasympathetic
b) (A) Centripetal (B) Afferent (C) PNS (D)
ANS (E) Parasympathetic
c) (A) Centrifugal (B) Afferent (C) SNS (D)
ANS (E) Parasympathetic
d) (A) Centripetal (B) Efferent (C) SNS (D)
ANS (E) Parasympathetic
2. The cerebrospinal fluid passes out from the
ventricle of medulla oblongata into the
space between meninges of brain through
a) Foramen of monro
b) Foramen of magnum
c) Foramen of magandii and luschaka
d) Foramen ovale
3. If cerebellum of man gets damaged, his
movement becomes
a) Shaky and speech becomes defective
b) Unbalanced, walk uncontrolled,
defective speech and intention tremor
c) Jerky and defective speech
d) Jerky and walk uncontrolled
4. Phrenic nerve is a
a) Cranial nerve b) Spinal nerve
c) Sciatic nerve d) Lumbar nerve
DPP - 2
5. The diagram shows a section through the
head showing the brain and part of the
spinal cord
Y
X
W
Z
Which structures carry out the functions
listed below?
Conscious Control of body
thought movements
and memory and posture
a) X W
b) W X
c) Y Z
d) Z Y
6. Excessive stimulation of vagus nerve in
humans may lead to
a) Hoarse voice
b) Peptic ulcers
c) Efficient digestion of proteins
d) Irregular contractions of diaphragm
7. Hippocampal lobes are the parts of
a) Olfactory lobes
b) Cerebrum
c) Cerebellum
d) Medulla oblongata
8. If Broca’s area is injured then what happens
firstly
a) Concerning speech muscles are
paralyzed
b) Speech stattered and not clear
c) Unable to speak
d) Only able to speak written word
62
9. The cavity of brain is lined by
a) Neural epithelium
b) Ependymal epithelium
c) Cerebrospinal fluid
d) Glandular epithelium
10. Hearing is controlled by
a) Cerebellum
b) Diencephalon
c) Frontal lobe of cerebrum
d) Temporal lobe of cerebrum
9. The cavity of brain is lined by
a) Neural epithelium
b) Ependymal epithelium
c) Cerebrospinal fluid
d) Glandular epithelium
10. Hearing is controlled by
a) Cerebellum
b) Diencephalon
c) Frontal lobe of cerebrum
d) Temporal lobe of cerebrum
63
3.1 SENSORY FUNCTIONS OF THE NERVOUS SYSTEM
In order to respond and maintain homeostasis, we must be able to detect that a change has happened
in the first place. The nervous system is well adapted to carry out this specific function. This overall
process of sensing and interpreting these signals is called sensation.
Stimuli from varying sources, and of different types, must be received and changed into the
electrochemical signals of the nervous system represented by changes in the membrane potential.
The sensory information is relayed to the central nervous system where it is integrated with other
sensory information, or sometimes higher cognitive functions, to become a conscious perception of
that stimulus. The central integration may then lead to a motor response.
Not all stimuli are used only for homeostasis maintenance, with sensory input playing a role in all
kinds of reflex and conscious responses as well.
3.1.1 Types of receptors
Stimuli in the environment activate specialized receptors in the peripheral nervous system. The
classification of receptors into types can be based on three different criteria: structure of the receptors,
location of the receptor relative to the stimuli they sense, and by the types of stimuli to which they
respond. Regardless of type, the function of these receptors is to transduce a stimulus from one
form of energy (chemical, physical, etc) into a change in the cell membrane potential that may or
may not create an action potential.
A. Structural receptor types
The cells that detect change in the environment can be neurons with free nerve endings, where
the dendrites are exposed to the surrounding tissue; neurons with encapsulated endings, where
supporting cells aid in the reception of stimuli; or specialized receptor cells, which have specific
structural components for detecting stimuli. Examples of neurons with free nerve endings are the
pain and temperature receptors in the dermis of the skin. Also in the dermis are encapsulated nerve
endings such as the lamellar corpuscle that sense pressure. The cells in the retina that receive light
stimuli are an example of specialized photoreceptor cells, not neurons that in turn can stimulate
an associated sensory neuron.
B. Locational receptor types
Receptors can also be classified based on their location relative to the stimuli. Exteroceptors are
receptors that receive input from the external environment, such as the lamellar corpuscles of the
dermis and photoreceptors of the eye that have already been mentioned. Interoceptors are those
that sense stimuli from the internal organs. Examples would include a stretch receptor in the wall of
an organ, such as those that sense the increase in blood pressure in the aorta or carotid artery or
detects stretch as the bladder fills with urine. Finally, proprioceptors are widely distributed receptors
in muscles, tendons and joint capsules that the body uses to determine position and movement of
structures, such as its limbs and fingers. Proprioceptors allow you to touch your finger to your nose,
even with your eyes closed.
UNIT 3 - NERVOUS SYSTEM III
3.1 SENSORY FUNCTIONS OF THE NERVOUS SYSTEM
In order to respond and maintain homeostasis, we must be able to detect that a change has happened
in the first place. The nervous system is well adapted to carry out this specific function. This overall
process of sensing and interpreting these signals is called sensation.
Stimuli from varying sources, and of different types, must be received and changed into the
electrochemical signals of the nervous system represented by changes in the membrane potential.
The sensory information is relayed to the central nervous system where it is integrated with other
sensory information, or sometimes higher cognitive functions, to become a conscious perception of
that stimulus. The central integration may then lead to a motor response.
Not all stimuli are used only for homeostasis maintenance, with sensory input playing a role in all
kinds of reflex and conscious responses as well.
3.1.1 Types of receptors
Stimuli in the environment activate specialized receptors in the peripheral nervous system. The
classification of receptors into types can be based on three different criteria: structure of the receptors,
location of the receptor relative to the stimuli they sense, and by the types of stimuli to which they
respond. Regardless of type, the function of these receptors is to transduce a stimulus from one
form of energy (chemical, physical, etc) into a change in the cell membrane potential that may or
may not create an action potential.
A. Structural receptor types
The cells that detect change in the environment can be neurons with free nerve endings, where
the dendrites are exposed to the surrounding tissue; neurons with encapsulated endings, where
supporting cells aid in the reception of stimuli; or specialized receptor cells, which have specific
structural components for detecting stimuli. Examples of neurons with free nerve endings are the
pain and temperature receptors in the dermis of the skin. Also in the dermis are encapsulated nerve
endings such as the lamellar corpuscle that sense pressure. The cells in the retina that receive light
stimuli are an example of specialized photoreceptor cells, not neurons that in turn can stimulate
an associated sensory neuron.
B. Locational receptor types
Receptors can also be classified based on their location relative to the stimuli. Exteroceptors are
receptors that receive input from the external environment, such as the lamellar corpuscles of the
dermis and photoreceptors of the eye that have already been mentioned. Interoceptors are those
that sense stimuli from the internal organs. Examples would include a stretch receptor in the wall of
an organ, such as those that sense the increase in blood pressure in the aorta or carotid artery or
detects stretch as the bladder fills with urine. Finally, proprioceptors are widely distributed receptors
in muscles, tendons and joint capsules that the body uses to determine position and movement of
structures, such as its limbs and fingers. Proprioceptors allow you to touch your finger to your nose,
even with your eyes closed.
UNIT 3 - NERVOUS SYSTEM III
64
Free nerve endings
Enclosed nerve endings
Unmyelinated axon
Cell body
a. Free nerve endings have
dendrites exposed to
surrounding tissueb. Encapsulated nerve endings
have connective tissue around
the dendrites that contribute to
sensation
c. Specialized receptor cells
sense their specific stimuli and,
in turn, stimulate a sensory
neuron
Layers of connective tissue
Synaptic vesicles
Myelinated axon
Cell body
Cell body
Sensory neuron
Synapse
Specialized receptor
cell (hair cell)
Stimulus
Structural receptor types
C. Functional receptor types
Lastly, receptors can be classified by the types of signals they transduce into changes in membrane
potential.
Chemoreceptors sense chemical stimuli, examples being taste, smell and the osmotic pressure of
the body’s extracellular fluids (the latter sensed by osmoreceptors).
Nociceptors are pain receptors. Although pain is primarily a chemical sense that detects the presence
of chemicals released during tissue damage, nociceptors are typically considered in a functional
category of their own. Nociceptors are found in most tissues throughout the body, exceptions being
the brain and possibly certain internal structures of organs.
Mechanoreceptors sense physical stimuli, such as pressure and vibration, as well as the sensation
of sound and pull of gravity. A specific example of a mechanoreceptors is the baroreceptors (pressure
receptors) found in the carotid arteries, which sense blood pressure.
Thermoreceptors are specific to sensing temperature and changes in temperature. Thermoreceptors
are found in two forms, those that respond most strongly to temperatures below normal body
temperature (cold thermoreceptors), and those that respond most strongly at temperatures above
normal body temperature (warm thermoreceptors). At normal body temperature, both types of
receptors are active, but there is generally no awareness of cold or warmth.
Free nerve endings
Enclosed nerve endings
Unmyelinated axon
Cell body
a. Free nerve endings have
dendrites exposed to
surrounding tissueb. Encapsulated nerve endings
have connective tissue around
the dendrites that contribute to
sensation
c. Specialized receptor cells
sense their specific stimuli and,
in turn, stimulate a sensory
neuron
Layers of connective tissue
Synaptic vesicles
Myelinated axon
Cell body
Cell body
Sensory neuron
Synapse
Specialized receptor
cell (hair cell)
Stimulus
Structural receptor types
C. Functional receptor types
Lastly, receptors can be classified by the types of signals they transduce into changes in membrane
potential.
Chemoreceptors sense chemical stimuli, examples being taste, smell and the osmotic pressure of
the body’s extracellular fluids (the latter sensed by osmoreceptors).
Nociceptors are pain receptors. Although pain is primarily a chemical sense that detects the presence
of chemicals released during tissue damage, nociceptors are typically considered in a functional
category of their own. Nociceptors are found in most tissues throughout the body, exceptions being
the brain and possibly certain internal structures of organs.
Mechanoreceptors sense physical stimuli, such as pressure and vibration, as well as the sensation
of sound and pull of gravity. A specific example of a mechanoreceptors is the baroreceptors (pressure
receptors) found in the carotid arteries, which sense blood pressure.
Thermoreceptors are specific to sensing temperature and changes in temperature. Thermoreceptors
are found in two forms, those that respond most strongly to temperatures below normal body
temperature (cold thermoreceptors), and those that respond most strongly at temperatures above
normal body temperature (warm thermoreceptors). At normal body temperature, both types of
receptors are active, but there is generally no awareness of cold or warmth.
65
Photoreceptors respond to electromagnetic radiation (light). Humans have the ability to sense
electromagnetic waves at wavelength between 400 and 700 nanometres, with different wavelengths
corresponding to different colours.
3.1.2 Types of senses
Because the central nervous system requires a significant amount of input in order to carry out
homeostatic functions, receptors are numerous. Some of these receptors are widely distributed
throughout body tissues (general or somesthetic senses), while others are localized to special
sense organs of the head, such as the eye or ear (special senses). Collectively the receptors and
associated neurons that sense and process information related to our somesthetic senses are
called the somatosensory system.
The receptors that provide information for somesthetic senses come in a variety of anatomical and
functional types. Each specific receptor will respond to only one type of functional signal (such as
mechanical or chemical, but not both). If the information is transmitted all the way to the brain’s
cortex, we perceive a sensation. The type or perception that this information leads to is called a
modality. There are four main modalities typically recognized as part of the somesthetic senses.
These include temperature, touch, pain (nociception), and position and movement (proprioception).
Yet each of these can be further subdivided into sub modalities (sometimes called stimulus
modalities). For example, the modality of pain can be subdivided into sharp, dull and aching.
General (Somesthetic) senses
Receptors are widely distributed throughout the body
Somatic senses
Information from skin,
muscles and joints
and organ capsules
Visceral senses
Information from
internal organs,
blood and body fluids
Types of information
Touch
Pain (nociception)
Temperature
Proprioception
Types of information
(examples)
Blood pressure
pH of fluids
Osmolarity of fluids
Stretch receptors in organs
The receptive field is the area from which a sensory receptor, and its corresponding neuron, can
detect a stimulus. The size of a receptive field might vary from a few square mm to tens of square
mm, depending on receptor type and location. With larger receptive fields, the CNS has less ability
to localize stimuli or to differentiate between multiple stimuli.
Photoreceptors respond to electromagnetic radiation (light). Humans have the ability to sense
electromagnetic waves at wavelength between 400 and 700 nanometres, with different wavelengths
corresponding to different colours.
3.1.2 Types of senses
Because the central nervous system requires a significant amount of input in order to carry out
homeostatic functions, receptors are numerous. Some of these receptors are widely distributed
throughout body tissues (general or somesthetic senses), while others are localized to special
sense organs of the head, such as the eye or ear (special senses). Collectively the receptors and
associated neurons that sense and process information related to our somesthetic senses are
called the somatosensory system.
The receptors that provide information for somesthetic senses come in a variety of anatomical and
functional types. Each specific receptor will respond to only one type of functional signal (such as
mechanical or chemical, but not both). If the information is transmitted all the way to the brain’s
cortex, we perceive a sensation. The type or perception that this information leads to is called a
modality. There are four main modalities typically recognized as part of the somesthetic senses.
These include temperature, touch, pain (nociception), and position and movement (proprioception).
Yet each of these can be further subdivided into sub modalities (sometimes called stimulus
modalities). For example, the modality of pain can be subdivided into sharp, dull and aching.
General (Somesthetic) senses
Receptors are widely distributed throughout the body
Somatic senses
Information from skin,
muscles and joints
and organ capsules
Visceral senses
Information from
internal organs,
blood and body fluids
Types of information
Touch
Pain (nociception)
Temperature
Proprioception
Types of information
(examples)
Blood pressure
pH of fluids
Osmolarity of fluids
Stretch receptors in organs
The receptive field is the area from which a sensory receptor, and its corresponding neuron, can
detect a stimulus. The size of a receptive field might vary from a few square mm to tens of square
mm, depending on receptor type and location. With larger receptive fields, the CNS has less ability
to localize stimuli or to differentiate between multiple stimuli.
66
Receptive
field 1
Receptive
field 3
Receptive
field 2
Individual sensory neurons that are in proximity to each other are bundled together into nerves that
enter the spinal cord through its posterior root of horn. The region of the skin that each spinal nerve
carries information from is called its dermatome. Because there are 31 spinal nerves, there are an
equal number of dermatomes, each named for the spinal nerve to which it sends information.
3.1.3 Reflexes
Reflexes are a unique category of responses because they do not require the higher centres used
for conscious or voluntary responses. Instead reflexes are involuntary, stereotyped (they are
repeatable under the same stimulus conditions) responses that occur quickly.
Categories of reflexes
Reflexes can either be visceral or somatic. Visceral reflexes involve a glandular or non-skeletal
muscular response carried out in internal organ such as the heart, blood vessels, or structures of
the GI tract. They utilize neurons of the autonomic nervous system to elicit their actions.
In contrast, somatic reflexes involve unconscious skeletal muscle motor responses. In doing so,
these reflexes utilize some of the same lower motor neurons (alpha motor neurons) used to control
skeletal muscle during conscious movement. Because reflexes are quick, it makes sense that somatic
reflexes are often meant to protect us from injury. As examples, reflexes contribute to the maintenance
of balance and rapid withdrawal of the hand or foot from damaging stimuli.
Somatic reflexes can either be intrinsic (present at birth) or learned. We will be focusing on intrinsic
reflexes, which occur as the result of normal human development. Learned reflexes are much
more complicated in their anatomical structure and result from repetitive actions, such as athletic
training. Reflexes can also be categorized by the number of synapses they involve (monosynaptic
reflex versus polysynaptic reflex) or the relative position of the sensory receptors to the responding
muscles (ipsilateral = same side of the body, contralateral = opposite sides of the body).
A. Stretch reflex
A common example of this reflex is the knee jerk reflex that is elicited by a rubber hammer striking
against the patellar tendon, such as during a physical exam. When the hammer strikes, it stretches
Receptive
field 1
Receptive
field 3
Receptive
field 2
Individual sensory neurons that are in proximity to each other are bundled together into nerves that
enter the spinal cord through its posterior root of horn. The region of the skin that each spinal nerve
carries information from is called its dermatome. Because there are 31 spinal nerves, there are an
equal number of dermatomes, each named for the spinal nerve to which it sends information.
3.1.3 Reflexes
Reflexes are a unique category of responses because they do not require the higher centres used
for conscious or voluntary responses. Instead reflexes are involuntary, stereotyped (they are
repeatable under the same stimulus conditions) responses that occur quickly.
Categories of reflexes
Reflexes can either be visceral or somatic. Visceral reflexes involve a glandular or non-skeletal
muscular response carried out in internal organ such as the heart, blood vessels, or structures of
the GI tract. They utilize neurons of the autonomic nervous system to elicit their actions.
In contrast, somatic reflexes involve unconscious skeletal muscle motor responses. In doing so,
these reflexes utilize some of the same lower motor neurons (alpha motor neurons) used to control
skeletal muscle during conscious movement. Because reflexes are quick, it makes sense that somatic
reflexes are often meant to protect us from injury. As examples, reflexes contribute to the maintenance
of balance and rapid withdrawal of the hand or foot from damaging stimuli.
Somatic reflexes can either be intrinsic (present at birth) or learned. We will be focusing on intrinsic
reflexes, which occur as the result of normal human development. Learned reflexes are much
more complicated in their anatomical structure and result from repetitive actions, such as athletic
training. Reflexes can also be categorized by the number of synapses they involve (monosynaptic
reflex versus polysynaptic reflex) or the relative position of the sensory receptors to the responding
muscles (ipsilateral = same side of the body, contralateral = opposite sides of the body).
A. Stretch reflex
A common example of this reflex is the knee jerk reflex that is elicited by a rubber hammer striking
against the patellar tendon, such as during a physical exam. When the hammer strikes, it stretches
67
the tendon, which pulls on the quadriceps femoris muscle. Because bones and tendon do not typically
pull muscles, the muscle “thinks” it is stretching very rapidly, and the reflex acts to counteract this
stretch. In doing so, the “knee jerk” occurs.
B. Flexor (withdrawal) reflex
Sensory receptors in the skin sense extreme temperature and the early signs of tissue damage. To
avoid further damage, information travels along the sensory fibres from the skin and into the posterior
(dorsal) horn of the spinal cord. Once in the spinal cord, the sensory fibres synapse with a variety of
interneurons that mediate the responses of the reflex. These responses included a strong initial
withdrawal of the flexor muscle (caused by activation of the alpha motor neurons), inhibition of the
extensor muscle (mediated through inhibitory interneurons), and sustained contraction of the flexor
(mediated by the spinal cord neuronal circuit). The sensory information will also travel to the brain to
develop a conscious awareness of the situation such that conscious decision making can take over
immediately after the reflex occurs.
C. Crossed-extensor reflex
Imagine what would happen if, when you stepped on a sharp object, it elicited a strong withdrawal
reflex of your leg. You would likely topple over. In order to prevent this from happening, as the flexor
(withdrawal) reflex involving the injured leg happens, an extension reflex of the opposite (contralateral)
leg occurs at the same time, creating a crossed extensor reflex. In this case, the ipsilateral limb
reacts with a withdrawal reflex (stimulating flexor muscles and inhibiting extensor muscles on same
side), but the contralateral extensor muscles contract so that the person can appropriately shift
balance to the opposite foot during the reflex.
SPECIAL SENSES
3.2 EYE
3.2.1 Anatomy
The eyes are located within the skull orbits, which provide protection for the eyes, as well as provide
a place to anchor the soft tissues that support the functions of the eye. The eyelids, with lashes at
their leading edges, help to protect the eye from abrasions by blocking particles that may get onto its
surface. From the inner surface of each lid, a thin mucus membrane known as the conjunctiva
folds in and covers the surface of the eye. Tears are produced by the lacrimal glands, which are
superior and lateral to the orbit in each eye, and they flow over the conjunctiva to wash away
particles that may have gotten past the lashes and the lids. Tears flow down through the lacrimal
ducts, located on the medial side of each orbit, into the nasal cavity.
3.2.2 Eye movement
Movement of the eye within the orbit is accomplished by the contraction of six extralocular muscles
that originate from the bones of the orbit and insert into the surface of the eye.
the tendon, which pulls on the quadriceps femoris muscle. Because bones and tendon do not typically
pull muscles, the muscle “thinks” it is stretching very rapidly, and the reflex acts to counteract this
stretch. In doing so, the “knee jerk” occurs.
B. Flexor (withdrawal) reflex
Sensory receptors in the skin sense extreme temperature and the early signs of tissue damage. To
avoid further damage, information travels along the sensory fibres from the skin and into the posterior
(dorsal) horn of the spinal cord. Once in the spinal cord, the sensory fibres synapse with a variety of
interneurons that mediate the responses of the reflex. These responses included a strong initial
withdrawal of the flexor muscle (caused by activation of the alpha motor neurons), inhibition of the
extensor muscle (mediated through inhibitory interneurons), and sustained contraction of the flexor
(mediated by the spinal cord neuronal circuit). The sensory information will also travel to the brain to
develop a conscious awareness of the situation such that conscious decision making can take over
immediately after the reflex occurs.
C. Crossed-extensor reflex
Imagine what would happen if, when you stepped on a sharp object, it elicited a strong withdrawal
reflex of your leg. You would likely topple over. In order to prevent this from happening, as the flexor
(withdrawal) reflex involving the injured leg happens, an extension reflex of the opposite (contralateral)
leg occurs at the same time, creating a crossed extensor reflex. In this case, the ipsilateral limb
reacts with a withdrawal reflex (stimulating flexor muscles and inhibiting extensor muscles on same
side), but the contralateral extensor muscles contract so that the person can appropriately shift
balance to the opposite foot during the reflex.
SPECIAL SENSES
3.2 EYE
3.2.1 Anatomy
The eyes are located within the skull orbits, which provide protection for the eyes, as well as provide
a place to anchor the soft tissues that support the functions of the eye. The eyelids, with lashes at
their leading edges, help to protect the eye from abrasions by blocking particles that may get onto its
surface. From the inner surface of each lid, a thin mucus membrane known as the conjunctiva
folds in and covers the surface of the eye. Tears are produced by the lacrimal glands, which are
superior and lateral to the orbit in each eye, and they flow over the conjunctiva to wash away
particles that may have gotten past the lashes and the lids. Tears flow down through the lacrimal
ducts, located on the medial side of each orbit, into the nasal cavity.
3.2.2 Eye movement
Movement of the eye within the orbit is accomplished by the contraction of six extralocular muscles
that originate from the bones of the orbit and insert into the surface of the eye.
68
Orbicularis
oculi muscie
Upper eyelid
Eyelashes
Cornea
Conjunctiva
Orbicularis
oculi muscle
Sclera
Inferior oblique muscle
Inferior rectus muscle
Lateral rectus muscle
Medial rectus muscle
Levator palpebrae
superioris muscle
Superior rectus muscle
Superior oblique muscle
Muscles that control eye movement
Any defect in one of the eyeball muscles (eg. Muscle may remain small or extra large than required)
causes strabismus or squint eyes. In this defect, eye ball remains inclined to any of the one side.
Muscles Effect of contraction Innervated by (including cranial nerve number)
Superior rectus Eye rotates to look up Occulomotor nerve (III)
Medial rectus Eye rotates to look medially Occulomotor (III)
Inferior rectus Eye rotates to look down Occulomotor (III)
Lateral rectus Eye rotates to look laterally Abducens (VI)
Superior oblique Medial rotation Trochlear (IV)
Inferior oblique Lateral rotation Occulomotor (III)
Orbicularis
oculi muscie
Upper eyelid
Eyelashes
Cornea
Conjunctiva
Orbicularis
oculi muscle
Sclera
Inferior oblique muscle
Inferior rectus muscle
Lateral rectus muscle
Medial rectus muscle
Levator palpebrae
superioris muscle
Superior rectus muscle
Superior oblique muscle
Muscles that control eye movement
Any defect in one of the eyeball muscles (eg. Muscle may remain small or extra large than required)
causes strabismus or squint eyes. In this defect, eye ball remains inclined to any of the one side.
Muscles Effect of contraction Innervated by (including cranial nerve number)
Superior rectus Eye rotates to look up Occulomotor nerve (III)
Medial rectus Eye rotates to look medially Occulomotor (III)
Inferior rectus Eye rotates to look down Occulomotor (III)
Lateral rectus Eye rotates to look laterally Abducens (VI)
Superior oblique Medial rotation Trochlear (IV)
Inferior oblique Lateral rotation Occulomotor (III)
69
3.2.3 Components of the eye
LENS: A transparent, ectodermal, biconvex lens is present just after iris. In frog, lens is spherical in
eyeball lens is connected by ciliary body with the help of “suspensory ligaments” called “zonula
of zinn” or zonules. These ligaments are flexible and this can slide the lens and can change its
focal length. Lens divides the cavity of eyeball into two chambers.
The anterior chamber, of anterior cavity is the space between the cornea and iris. The posterior
chamber sits between the iris and the lens. Both the anterior and posterior chambers are filled with
a watery fluid called the aqueous humour. The posterior vitreous chamber (also posterior cavity) is
posterior to the lens and is filled with a more viscous fluid called the vitreous humour (vitreous
body). In this fluid 99% water, some salts, a mucoprotein called vitrin and a mucopolysaccharide.
Hyaluronic acid is present. Gelatinous nature of vitreous humour depends upon fibrillar protein and
hyaluronic acid. It is formed during embryonic stage. In this chamber Hyalocytes cells are found.
Aqueous humour and vitreous humour both are secreted by the glands of ciliary body. Aqueous
humour leak out by canal of schlemm into blood capillaries and again reach up to their veins.
Both these fluids maintain proper pressure inside the cavity of the eye ball. These check the eye ball
from collapsing. If this canal of schlemm is blocked by any reason and fluids do not return back to
veins fluid is increased in the chambers of eye. When amount of this humour is increased in the eye
chambers then pressure is increased inside the eye ball thus retina pressure is increased. This is
known as Glaucoma.
A thin Hyaloid canal or Cloquet’s canal is also found in vitreous humor from blind spot to central
point of lens, it provide nourishment to the developing lens which gradually atrophied.
The eye itself is a hollow sphere composed of three layers of tissue. The outermost layer is the
fibrous tunic which is the white sclera and clear cornea. The two parts of the fibrous tunic are
continuous, though they have different properties. The sclera accounts for 5/6 of the surface of the
eye, most of which is not visible (though humans are unique in having so much of the “white of the
eye” visible). The cornea covers the anterior region of the eye and allows light to pass into the eye
where it will eventually stimulate photoreceptors. The next layer of the eye is the vascular tunic,
which is mostly composed of the choroid, a highly vascularized connective tissue that provides a
blood supply to the adjacent tissue. The choroid is posterior to the ciliary body, a muscular structure
that is attached to the lens by the suspensory ligament. The ciliary body focuses light on the back
of the eye. Overlaying the ciliary body, and visible in the anterior eye, is the iris, the coloured part of
the eye that opens in the center as the pupil. The innermost layer of the eye is the neural tunic,
which is the retina or the nervous tissue that is responsible for photoreception.
3.2.3 Components of the eye
LENS: A transparent, ectodermal, biconvex lens is present just after iris. In frog, lens is spherical in
eyeball lens is connected by ciliary body with the help of “suspensory ligaments” called “zonula
of zinn” or zonules. These ligaments are flexible and this can slide the lens and can change its
focal length. Lens divides the cavity of eyeball into two chambers.
The anterior chamber, of anterior cavity is the space between the cornea and iris. The posterior
chamber sits between the iris and the lens. Both the anterior and posterior chambers are filled with
a watery fluid called the aqueous humour. The posterior vitreous chamber (also posterior cavity) is
posterior to the lens and is filled with a more viscous fluid called the vitreous humour (vitreous
body). In this fluid 99% water, some salts, a mucoprotein called vitrin and a mucopolysaccharide.
Hyaluronic acid is present. Gelatinous nature of vitreous humour depends upon fibrillar protein and
hyaluronic acid. It is formed during embryonic stage. In this chamber Hyalocytes cells are found.
Aqueous humour and vitreous humour both are secreted by the glands of ciliary body. Aqueous
humour leak out by canal of schlemm into blood capillaries and again reach up to their veins.
Both these fluids maintain proper pressure inside the cavity of the eye ball. These check the eye ball
from collapsing. If this canal of schlemm is blocked by any reason and fluids do not return back to
veins fluid is increased in the chambers of eye. When amount of this humour is increased in the eye
chambers then pressure is increased inside the eye ball thus retina pressure is increased. This is
known as Glaucoma.
A thin Hyaloid canal or Cloquet’s canal is also found in vitreous humor from blind spot to central
point of lens, it provide nourishment to the developing lens which gradually atrophied.
The eye itself is a hollow sphere composed of three layers of tissue. The outermost layer is the
fibrous tunic which is the white sclera and clear cornea. The two parts of the fibrous tunic are
continuous, though they have different properties. The sclera accounts for 5/6 of the surface of the
eye, most of which is not visible (though humans are unique in having so much of the “white of the
eye” visible). The cornea covers the anterior region of the eye and allows light to pass into the eye
where it will eventually stimulate photoreceptors. The next layer of the eye is the vascular tunic,
which is mostly composed of the choroid, a highly vascularized connective tissue that provides a
blood supply to the adjacent tissue. The choroid is posterior to the ciliary body, a muscular structure
that is attached to the lens by the suspensory ligament. The ciliary body focuses light on the back
of the eye. Overlaying the ciliary body, and visible in the anterior eye, is the iris, the coloured part of
the eye that opens in the center as the pupil. The innermost layer of the eye is the neural tunic,
which is the retina or the nervous tissue that is responsible for photoreception.
70
Posterior chamber
Anterior chamber
Iris
Pupil
Cornea
Lens
Suspensory ligament
Schlemm’s canal
Limbus
Ciliary body
Ciliary muscle
Ciliary processOra serrata Hyaloid canal
Central retinal
blood vessels
Optic nerves
(Carnial nerve II)
Optic disc area (blind spot)
Fovea centralis
Retina
Choroid
Sclera
Vitreous chamber
Cornea
Corneal epithelium
Corneal endothelium
Aqueous humorANTERIOR
Anterior chamber
Posterior chamber
Anterior segment
Scleral venous sinus
Limbus (corneal-scleral junction)
Anterior ciliary vein
Bulbar conjunctive
Sclera
Iris
Lens
epithelium
Lens
Posterior
segment
containing
vitreous
humor
Ciliary zonule
Ciliary body
Ciliary
process
Ciliary
muscle
Cornea Lens
A. Fibrous tunic
Cornea: It is covered by st. non-keratinized squamous epithelium. The joint between cornea and
sclera is called limbus or sclero-corneal junction. Cornea transplantation is successful because
it lacks blood vessels.
Sclera: It is made up of white, hard, opaque thick fibrous connective tissue in rabbit but in frog, it is
made up of cartilage. It is the inner portion of eye ball, non-vascularised, mesodermal in origin.
Inner layer of eyelids remain streched over limbus in the form of translucent membrane, called
conjunctiva. It is made up of epidermis of skin and is the thinnest epidermis in animal body.
Posterior chamber
Anterior chamber
Iris
Pupil
Cornea
Lens
Suspensory ligament
Schlemm’s canal
Limbus
Ciliary body
Ciliary muscle
Ciliary processOra serrata Hyaloid canal
Central retinal
blood vessels
Optic nerves
(Carnial nerve II)
Optic disc area (blind spot)
Fovea centralis
Retina
Choroid
Sclera
Vitreous chamber
Cornea
Corneal epithelium
Corneal endothelium
Aqueous humorANTERIOR
Anterior chamber
Posterior chamber
Anterior segment
Scleral venous sinus
Limbus (corneal-scleral junction)
Anterior ciliary vein
Bulbar conjunctive
Sclera
Iris
Lens
epithelium
Lens
Posterior
segment
containing
vitreous
humor
Ciliary zonule
Ciliary body
Ciliary
process
Ciliary
muscle
Cornea Lens
A. Fibrous tunic
Cornea: It is covered by st. non-keratinized squamous epithelium. The joint between cornea and
sclera is called limbus or sclero-corneal junction. Cornea transplantation is successful because
it lacks blood vessels.
Sclera: It is made up of white, hard, opaque thick fibrous connective tissue in rabbit but in frog, it is
made up of cartilage. It is the inner portion of eye ball, non-vascularised, mesodermal in origin.
Inner layer of eyelids remain streched over limbus in the form of translucent membrane, called
conjunctiva. It is made up of epidermis of skin and is the thinnest epidermis in animal body.
71
B. Vascular tunic
Melanin is found in this layer and thus, eye looks like green, blue, brown, black in colour. Eyes of
rabbit are red due to red melanin pigments.
Choroid layer: Lies below sclera, contains abundant pigment cells and blood vessels, dark brown
in color, darkens the cavity of eyeball to prevent internal reflection of light and nourishes the retina.
Ciliary body: Lower swollen portion below limbus, has ciliary processes which project into eyeball,
has ciliary muscles (i) circular (ii) meridional. Inner end of meridional is attached to choroid and
outer end at the junction of sclera and cornea.
Iris: A coloured screen formed when the vascular tunic separates from sclera (just after cornea)
and inclines towards innerside. Iris muscles are ectodermal in origin where as other body muscles
are mesodermal in origin. Pupil is the aperture where light rays enter the eyeball. Iris controls the
intensity of light by increasing or decreasing the diameter of pupil i.e. Iris acts as diaphragm of a
camera. The parasympathetic fibres constrict and sympathetic fibre dilate the pupil.
Muscles related with iris are:
(i) Radial dilatory muscles: Outer unstriated muscles expanded in the iris breadthwise. Iris becomes
constricted if these muscles contract and diameter of pupil is increased at that time. It happens in
dim light, it is called Mydriasis.
(ii) Circular sphincter muscles: Scattered in inner part of iris, contraction in high light causes iris
to expand breadthwise and diameter of pupil decreases. It is called miosis.
C. Neural tunic
It is the inner most layer of eye ball with 3 parts:
(i) Pars Ciliaris: Attached with ciliary bodies, there are present spine like projections at the
surfae of ciliary body, these are called “Orra serrata”.
(ii) Pars iridica: Lies just after the iris. It has a layer of pigmented cells. Pars iridica and pars
ciliaris are made up of simple cuboidal epithelium.
(iii) Pars optica: Also called retina. It is the part just below the choroid layer.
3.2.4 Retina
The retina is composed of a several layers and contains specialized cells for the initial processing of
visual stimuli, with the rest of the visual processing occuring in the central nervous system.
The photoreceptors are found in the retinal layer closest to the back of the eye (outermost layer)
when stimulated by light energy, they change their membrane potential and alter the amount of
neurotransmitter released onto the bipolar cells. The bipolar cells connect to the retinal ganglion
cells (RGC) where amacrine cells also contribute to retinal processing such as contrast
enhancement and edge detection. The axons of RGCs, which are lying at the innermost aspects of
the retina, collect at the optic disc and leave the eye as the optic nerve. Because of the axons
passing through the wall of the eye at the optic disc, there are no photoreceptors resulting in a “blind
spot” in the retina. The blind spot in either reting falls in the medial retina and does not process
corresponding regions of the visual field.
B. Vascular tunic
Melanin is found in this layer and thus, eye looks like green, blue, brown, black in colour. Eyes of
rabbit are red due to red melanin pigments.
Choroid layer: Lies below sclera, contains abundant pigment cells and blood vessels, dark brown
in color, darkens the cavity of eyeball to prevent internal reflection of light and nourishes the retina.
Ciliary body: Lower swollen portion below limbus, has ciliary processes which project into eyeball,
has ciliary muscles (i) circular (ii) meridional. Inner end of meridional is attached to choroid and
outer end at the junction of sclera and cornea.
Iris: A coloured screen formed when the vascular tunic separates from sclera (just after cornea)
and inclines towards innerside. Iris muscles are ectodermal in origin where as other body muscles
are mesodermal in origin. Pupil is the aperture where light rays enter the eyeball. Iris controls the
intensity of light by increasing or decreasing the diameter of pupil i.e. Iris acts as diaphragm of a
camera. The parasympathetic fibres constrict and sympathetic fibre dilate the pupil.
Muscles related with iris are:
(i) Radial dilatory muscles: Outer unstriated muscles expanded in the iris breadthwise. Iris becomes
constricted if these muscles contract and diameter of pupil is increased at that time. It happens in
dim light, it is called Mydriasis.
(ii) Circular sphincter muscles: Scattered in inner part of iris, contraction in high light causes iris
to expand breadthwise and diameter of pupil decreases. It is called miosis.
C. Neural tunic
It is the inner most layer of eye ball with 3 parts:
(i) Pars Ciliaris: Attached with ciliary bodies, there are present spine like projections at the
surfae of ciliary body, these are called “Orra serrata”.
(ii) Pars iridica: Lies just after the iris. It has a layer of pigmented cells. Pars iridica and pars
ciliaris are made up of simple cuboidal epithelium.
(iii) Pars optica: Also called retina. It is the part just below the choroid layer.
3.2.4 Retina
The retina is composed of a several layers and contains specialized cells for the initial processing of
visual stimuli, with the rest of the visual processing occuring in the central nervous system.
The photoreceptors are found in the retinal layer closest to the back of the eye (outermost layer)
when stimulated by light energy, they change their membrane potential and alter the amount of
neurotransmitter released onto the bipolar cells. The bipolar cells connect to the retinal ganglion
cells (RGC) where amacrine cells also contribute to retinal processing such as contrast
enhancement and edge detection. The axons of RGCs, which are lying at the innermost aspects of
the retina, collect at the optic disc and leave the eye as the optic nerve. Because of the axons
passing through the wall of the eye at the optic disc, there are no photoreceptors resulting in a “blind
spot” in the retina. The blind spot in either reting falls in the medial retina and does not process
corresponding regions of the visual field.
72
Back of eye
Front of eye
Sclera
Choroid
Pigment epithelium
Rod and cone outer
segments
Rod and cone nuclei
Bipolar cells
Ganglion cells
Nerve fibers to
optic nerve
Vitreous body
Pigment epithelium
Photorecetors:
Rod
Cone
Transmission
of rod signals
Transmission
of cone signals
Bipolar cell
Horizontal cell
Amacrine cell
Ganglion cell
To optic nerve
Nerve fibers
Direction of light
Layers of the retina
At the exact centre of the retina is a point where light is focused by the lens and the greatest visual
acuity is found. This is known as the fovea and it is a small dimple in the layers of the retina where
there are no blood vessels, ganglion cells or bipolar cells to interrupt light reaching the receptor
cells. Because more light passes to the receptor cells at the fovea, it is in this region that visual
acuity is the greatest. From this central point of the retins, visual acuity drops off towards the peripheral
retina.
A large part of neural function to support the visual system is concerned with moving the eyes and
head so that important visual stimuli are centered on the fovea of the retina.
Retina
Capillary
Bipolar cells
Photoreceptors
Pigment
epithelium
FoveaGanglion cells
Anatomy of the fovea
Back of eye
Front of eye
Sclera
Choroid
Pigment epithelium
Rod and cone outer
segments
Rod and cone nuclei
Bipolar cells
Ganglion cells
Nerve fibers to
optic nerve
Vitreous body
Pigment epithelium
Photorecetors:
Rod
Cone
Transmission
of rod signals
Transmission
of cone signals
Bipolar cell
Horizontal cell
Amacrine cell
Ganglion cell
To optic nerve
Nerve fibers
Direction of light
Layers of the retina
At the exact centre of the retina is a point where light is focused by the lens and the greatest visual
acuity is found. This is known as the fovea and it is a small dimple in the layers of the retina where
there are no blood vessels, ganglion cells or bipolar cells to interrupt light reaching the receptor
cells. Because more light passes to the receptor cells at the fovea, it is in this region that visual
acuity is the greatest. From this central point of the retins, visual acuity drops off towards the peripheral
retina.
A large part of neural function to support the visual system is concerned with moving the eyes and
head so that important visual stimuli are centered on the fovea of the retina.
Retina
Capillary
Bipolar cells
Photoreceptors
Pigment
epithelium
FoveaGanglion cells
Anatomy of the fovea
73
Photoreceptor cells
Light falling on the retina causes chemical changes to pigment molecules (called opsins) in
photoreceptors ultimately leading to a change in the activity of the retinal ganglion cells. Photoreceptor
cells have two parts, the inner segment and the outer segment.
Outer
segment
Rod
Cone
Inner
segment
Cell body
Stalk
Mitochondria
Nucleus
Synaptic
vesicles
Rods
Cones
Structure of the photoreceptor cells
The inner segment contains the nucleus and other common organelles of a cell while the outer
segment is a specialized region of the cell where photoreception takes place. There are two types of
photoreceptors, rods and cones, based on the shape of their outer segment. The rod shaped outer
segments of rod photoreceptors contains a stack of membrane bound discs that contain a
photosensitive opsin pigment called rhodopsin, which is sensitive to a wide bandwidth of light
(white light). The cone shaped outer segment of cone cells contain one of three photosensitive
opsin pigments, called photopsins. Each of the three photopsin are sensitive to a particular bandwidth
of light, corresponding to the colours of red, green or blue, allowing for the ability to distinguish
colour.
When a photoreceptor cell is activated by a photon near the wavelength it is sensitive to, energy
from the light creates a change in its opsin molecule called photoisomerization. Photoisomerisation
is the first step in a process that ultimately leads to a change in membrane potential of the
photoreceptor. Until the opsin is changed back to its original shape, the photoreceptor cell cannot
respond to light energy, which is called bleaching. When a large group of opsins are bleached,
vision will be affected until enough opsins can return to the receptive state. You may have experienced
this after the bright flash from a camera.
3.2.5 Working of eye
A. Focusing light on the retina
For retina to transmit the most appropriate information to the brain, the light rays must land on the
retinal cells in focus and with sppropriate intensity. The cornea, pupil (the center of the iris) and the
lens are responsible for meeting these requirements.
Photoreceptor cells
Light falling on the retina causes chemical changes to pigment molecules (called opsins) in
photoreceptors ultimately leading to a change in the activity of the retinal ganglion cells. Photoreceptor
cells have two parts, the inner segment and the outer segment.
Outer
segment
Rod
Cone
Inner
segment
Cell body
Stalk
Mitochondria
Nucleus
Synaptic
vesicles
Rods
Cones
Structure of the photoreceptor cells
The inner segment contains the nucleus and other common organelles of a cell while the outer
segment is a specialized region of the cell where photoreception takes place. There are two types of
photoreceptors, rods and cones, based on the shape of their outer segment. The rod shaped outer
segments of rod photoreceptors contains a stack of membrane bound discs that contain a
photosensitive opsin pigment called rhodopsin, which is sensitive to a wide bandwidth of light
(white light). The cone shaped outer segment of cone cells contain one of three photosensitive
opsin pigments, called photopsins. Each of the three photopsin are sensitive to a particular bandwidth
of light, corresponding to the colours of red, green or blue, allowing for the ability to distinguish
colour.
When a photoreceptor cell is activated by a photon near the wavelength it is sensitive to, energy
from the light creates a change in its opsin molecule called photoisomerization. Photoisomerisation
is the first step in a process that ultimately leads to a change in membrane potential of the
photoreceptor. Until the opsin is changed back to its original shape, the photoreceptor cell cannot
respond to light energy, which is called bleaching. When a large group of opsins are bleached,
vision will be affected until enough opsins can return to the receptive state. You may have experienced
this after the bright flash from a camera.
3.2.5 Working of eye
A. Focusing light on the retina
For retina to transmit the most appropriate information to the brain, the light rays must land on the
retinal cells in focus and with sppropriate intensity. The cornea, pupil (the center of the iris) and the
lens are responsible for meeting these requirements.
74
When light moves from one medium (such as air) into another medium (such as the cornea or lens),
any rays not entering at a 90 degree angle will be refracted, or bent. Because both the cornea and
lens have curved surfaces, they refract some of the light rays entering the eye, in doing so, they
compress the image of what we see so that a large amount of visual information can be processed
by a small amount of retinal tissue. The cornea refracts more light than the lens does because its
surface is more curved, but the lens has the ability to change its shape, and therefore fine tune the
amount of refraction necessary to focus the light rays on the retina. This process is known as
accomodation.
The lens changes its shape in response to changes in tension of the ciliary muscles on the suspensory
ligamnets (also called zonules) that hold the lens in place. When the ciliary muscles contract, the
suspensory ligaments are less taught, causing the lens to become slightly more spherical and
refract light more. This is what happens when pbjects that are being viewed are close, or moved
closer. Light coming from objects that are far away do not require as much refraction and are
viewed with the ciliary muscles relaxed and more tension on the lens, which makes it more oblong.
Vitreous body
Retina
Air
Lens
Aqueous humor
Cornea
The refraction of light rays as they pass through the cornea and lens
Along with accomodation of the lens when objects are near, the pupil also tends to constrict to allow
less peripheral light to enter the posterior chamber of the eye. In doing so, objects can be viewed
more crisply. The pupil will also constrict when conditions are bright and dilate under low light
conditions. This way the retina can receive an appropriate amount of light to activate its photoreceptors
without bleaching them with too much light.
Ciliary muscle
relaxed
Lens thins
Suspensory
ligament taut
a. Distant vision (emmetropia)
Ciliary muscle
contracted
Lens thickens
Suspensory ligament relaxed
b. Near vision (accommodation)
When light moves from one medium (such as air) into another medium (such as the cornea or lens),
any rays not entering at a 90 degree angle will be refracted, or bent. Because both the cornea and
lens have curved surfaces, they refract some of the light rays entering the eye, in doing so, they
compress the image of what we see so that a large amount of visual information can be processed
by a small amount of retinal tissue. The cornea refracts more light than the lens does because its
surface is more curved, but the lens has the ability to change its shape, and therefore fine tune the
amount of refraction necessary to focus the light rays on the retina. This process is known as
accomodation.
The lens changes its shape in response to changes in tension of the ciliary muscles on the suspensory
ligamnets (also called zonules) that hold the lens in place. When the ciliary muscles contract, the
suspensory ligaments are less taught, causing the lens to become slightly more spherical and
refract light more. This is what happens when pbjects that are being viewed are close, or moved
closer. Light coming from objects that are far away do not require as much refraction and are
viewed with the ciliary muscles relaxed and more tension on the lens, which makes it more oblong.
Vitreous body
Retina
Air
Lens
Aqueous humor
Cornea
The refraction of light rays as they pass through the cornea and lens
Along with accomodation of the lens when objects are near, the pupil also tends to constrict to allow
less peripheral light to enter the posterior chamber of the eye. In doing so, objects can be viewed
more crisply. The pupil will also constrict when conditions are bright and dilate under low light
conditions. This way the retina can receive an appropriate amount of light to activate its photoreceptors
without bleaching them with too much light.
Ciliary muscle
relaxed
Lens thins
Suspensory
ligament taut
a. Distant vision (emmetropia)
Ciliary muscle
contracted
Lens thickens
Suspensory ligament relaxed
b. Near vision (accommodation)
75
B. Light and dark adaptation
Because rhodopsin found in the rod cells is most sensitive to white light while the cone cells are
color specific, rods are suited for vision in low light conditions and cones are suited for brighter
conditions. In normal sunlight, rhodopsin will be constantly bleached and the cones are active. In a
darkened room, there is not enough light to activate cone opsins, and vision is entirely dependent
on rods. Rods are so sensitive to light that a single photon can result in an action potential from the
corresponding RGC. The three cone photopsins, being sensitive to different wavelength of light,
can aid in colour vision. By comparing the activity of the three different cones, the brain can extract
color information from visual stimuli. Sincerods are bleached when cones are active and cones
cannot react to low intensity light, rods result in monochromatic vision. In a dark room, everything
appears as a shade of gray shadow. If you think that you can see colors in the dark, it is most likely
because your brain knows what color something is and relies on that memory. If you are walking
through your dark living room and you are certain that the couch appears green, this is because you
already know what color it is, not because you percieve it with rod photoreceptors.
C. Changes in vision
Sometimes the structures of the eye do not refract light appropriately, such that it focuses either in
front of (myopia) or behind (hyperopia) the retina. This can happen, for instance, when the eye is not
perfetly round. In order to correct for abnormalities in light refraction, glasses or contact lenses can
be added to the system to better focus light on the retina and improve vision.
Focal plane
Uncorrected
CorrectedConvex lens Concave lens
a. Emmetropia (normal)b. Hyperopia (farsiqhtedness)c. Myopia (nearsiqhtedness)
Focal plane
Uncorrected
Focal plane
Normal light refraction leads to the light rays converging on the retina (a). in the case of hyperopia,
the light rays focus behind the retina. This is corrected using a convex lens to begin to bend the light
before it reaches the cornea (b). in the case of myopia, the light rays focus in front of the retina. This
is corrected using a concave lens to diverge the light rays before it reaches the cornea.
B. Light and dark adaptation
Because rhodopsin found in the rod cells is most sensitive to white light while the cone cells are
color specific, rods are suited for vision in low light conditions and cones are suited for brighter
conditions. In normal sunlight, rhodopsin will be constantly bleached and the cones are active. In a
darkened room, there is not enough light to activate cone opsins, and vision is entirely dependent
on rods. Rods are so sensitive to light that a single photon can result in an action potential from the
corresponding RGC. The three cone photopsins, being sensitive to different wavelength of light,
can aid in colour vision. By comparing the activity of the three different cones, the brain can extract
color information from visual stimuli. Sincerods are bleached when cones are active and cones
cannot react to low intensity light, rods result in monochromatic vision. In a dark room, everything
appears as a shade of gray shadow. If you think that you can see colors in the dark, it is most likely
because your brain knows what color something is and relies on that memory. If you are walking
through your dark living room and you are certain that the couch appears green, this is because you
already know what color it is, not because you percieve it with rod photoreceptors.
C. Changes in vision
Sometimes the structures of the eye do not refract light appropriately, such that it focuses either in
front of (myopia) or behind (hyperopia) the retina. This can happen, for instance, when the eye is not
perfetly round. In order to correct for abnormalities in light refraction, glasses or contact lenses can
be added to the system to better focus light on the retina and improve vision.
Focal plane
Uncorrected
CorrectedConvex lens Concave lens
a. Emmetropia (normal)b. Hyperopia (farsiqhtedness)c. Myopia (nearsiqhtedness)
Focal plane
Uncorrected
Focal plane
Normal light refraction leads to the light rays converging on the retina (a). in the case of hyperopia,
the light rays focus behind the retina. This is corrected using a convex lens to begin to bend the light
before it reaches the cornea (b). in the case of myopia, the light rays focus in front of the retina. This
is corrected using a concave lens to diverge the light rays before it reaches the cornea.
76
D. Processing visual information
The photoreceptors, and other neuronal cells of the retina, send varied types of information to the
brain. These include light intensity, colors and the spatial distribution of the information received. All
of this information is then carried along the optic nerve and into the optic tract to be distributed to
nuclei in the brain. At the point where the optic nerve becomes the optic tract, the optic chiasm is
found. At this point, fibers carrying information from the nasal half of the retina on each side decussate
(cross over) such that the information from the nasal half of the retina of the left eye crosses over to
the right side of the brain and vice versa. In doing so, the left side of the brain receives information
from the right visual field of each eye, and the right side of the brain receives information from the
left visual field of each eye. This matches the sidedness of the brain to motor control. For example,
visual information from the left side of the body, and motor control of the left limbs, are both processed
by the right hemisphere of the brain.
Left visual
field
Right visual
field
Nasal
Temporal
Left eye
Optic nerve
Optic tract
Optic radiation
Temporal
Right eye
Depiction of how visual information has sidedness in the brain
Visual information from the optic tract is sent to a variety of nuclei in the brain. These nuclei, along with the type of processing they are involved in are summarized is table below.
Brain structures involved in visual processing
Nuclei Role
Lateral geniculate nucleus of the thalamus Project to the occipital lobe for processing of
visual perception
Superior colliculus Control of eye movements
Pretectum Pupillary light reflex
Suprachiasmatic nucleus of the hypothalamus. Hormonal control.
D. Processing visual information
The photoreceptors, and other neuronal cells of the retina, send varied types of information to the
brain. These include light intensity, colors and the spatial distribution of the information received. All
of this information is then carried along the optic nerve and into the optic tract to be distributed to
nuclei in the brain. At the point where the optic nerve becomes the optic tract, the optic chiasm is
found. At this point, fibers carrying information from the nasal half of the retina on each side decussate
(cross over) such that the information from the nasal half of the retina of the left eye crosses over to
the right side of the brain and vice versa. In doing so, the left side of the brain receives information
from the right visual field of each eye, and the right side of the brain receives information from the
left visual field of each eye. This matches the sidedness of the brain to motor control. For example,
visual information from the left side of the body, and motor control of the left limbs, are both processed
by the right hemisphere of the brain.
Left visual
field
Right visual
field
Nasal
Temporal
Left eye
Optic nerve
Optic tract
Optic radiation
Temporal
Right eye
Depiction of how visual information has sidedness in the brain
Visual information from the optic tract is sent to a variety of nuclei in the brain. These nuclei, along with the type of processing they are involved in are summarized is table below.
Brain structures involved in visual processing
Nuclei Role
Lateral geniculate nucleus of the thalamus Project to the occipital lobe for processing of
visual perception
Superior colliculus Control of eye movements
Pretectum Pupillary light reflex
Suprachiasmatic nucleus of the hypothalamus. Hormonal control.
77
The majority of the visual information flows through the lateral geniculate nucleus of the thalamus into
the occipital lobe for perception of vision. From here fibers will carry some information to regions of the
parietal and temporal lobes, called the visual association areas. These areas contribute to object
recognition (such as recognizing a face) and motion processing (such as catching a moving ball).
3.2.6 Types of vision
(a) Monocular vision or panoramic vision: Most vertebrates have their eyes on the lateral sides
of head and due to this animal is capable to see large area of both sides. It is called monocular
vision. Eg. Rabbit, frog, horse (most of the herbivorous animals have this type of vision).
(b) Binocular vision: Most carnivorous mammals have eyes in front of their heads and side by
side so as to focus on one object by both the eyes. It is called binocular vision. Eg. Man,
monkeys and apes.
(c) Stereoscopic vision: It is three dimensional vision found in human.
(d) Telescopic vision: this is found in birds.
– Sharpest vision is found in eagle while shortest sight is found in monkey.
3.2.7 Eye disorders
A. Hypermatropia (far sightedness): In this defect of eye, person is able to see objects placed at
far distance but is unable to see objects closer to him or her. This defect is due to small size of
eyeball or flatness of lens. Image is formed behind the retina. To cure this defect person should
wear convex lenses in spectacles. Sometimes in old age this defect may occur due to reduction in
the flexibility of lens or ciliary body, then it is known as presbyopia.
B. Myopia or near sightedness or short sightedness: In this defect of eye, person is able to see
objects near/ close to him or her but is unable to see objects placed at far distance. This is due to
enlargement of eyeball or increased convexity of lens. In this defect image is formed before the
retina because light rays coming from distant objects converge before retina. To overcome this
defect person should wear concave lenses in spectacles.
C. Astigmatism: In this defect curvature of cornea is changed as a result of that light rays do not
focus on macula lutea but somewhere else, causing incomplete and blurred vision. This defect may
be cured by cylindrical lenses.
D. Xerophthalmia: It is due to keratinisation of conjunctiva and cornea, and conjunctiva becomes
solid. It is also due to deficiency of vitamin A.
E. Night blindness: This is due to deficiency of vitamin A. In this disorder synthesis of rhodopsin is
reduced and a person is unable to see in dim light or night.
The majority of the visual information flows through the lateral geniculate nucleus of the thalamus into
the occipital lobe for perception of vision. From here fibers will carry some information to regions of the
parietal and temporal lobes, called the visual association areas. These areas contribute to object
recognition (such as recognizing a face) and motion processing (such as catching a moving ball).
3.2.6 Types of vision
(a) Monocular vision or panoramic vision: Most vertebrates have their eyes on the lateral sides
of head and due to this animal is capable to see large area of both sides. It is called monocular
vision. Eg. Rabbit, frog, horse (most of the herbivorous animals have this type of vision).
(b) Binocular vision: Most carnivorous mammals have eyes in front of their heads and side by
side so as to focus on one object by both the eyes. It is called binocular vision. Eg. Man,
monkeys and apes.
(c) Stereoscopic vision: It is three dimensional vision found in human.
(d) Telescopic vision: this is found in birds.
– Sharpest vision is found in eagle while shortest sight is found in monkey.
3.2.7 Eye disorders
A. Hypermatropia (far sightedness): In this defect of eye, person is able to see objects placed at
far distance but is unable to see objects closer to him or her. This defect is due to small size of
eyeball or flatness of lens. Image is formed behind the retina. To cure this defect person should
wear convex lenses in spectacles. Sometimes in old age this defect may occur due to reduction in
the flexibility of lens or ciliary body, then it is known as presbyopia.
B. Myopia or near sightedness or short sightedness: In this defect of eye, person is able to see
objects near/ close to him or her but is unable to see objects placed at far distance. This is due to
enlargement of eyeball or increased convexity of lens. In this defect image is formed before the
retina because light rays coming from distant objects converge before retina. To overcome this
defect person should wear concave lenses in spectacles.
C. Astigmatism: In this defect curvature of cornea is changed as a result of that light rays do not
focus on macula lutea but somewhere else, causing incomplete and blurred vision. This defect may
be cured by cylindrical lenses.
D. Xerophthalmia: It is due to keratinisation of conjunctiva and cornea, and conjunctiva becomes
solid. It is also due to deficiency of vitamin A.
E. Night blindness: This is due to deficiency of vitamin A. In this disorder synthesis of rhodopsin is
reduced and a person is unable to see in dim light or night.
78
F. Color blindness: it is genetic disorder of X chromosomes. It is due to recessive gene. Color
blind persons cannot differentiate in red and green color.
G. Cataract: In this defect, lens becomes more solid, brown or more flat. It occurs in old age mostly.
The lens become opaque, and reduces its power of accommodation. At this stage person cannot
see. A new lens is administered in place of defective lens by operation.
H. Glaucoma: If the canal of schlemm is blocked in eyeball, aqueous humour cannot return to veins
again as a pressure is increased in eye chambers ad retina is damaged and person becomes totally
blind.
I. Trachoma: A watery liquid oozes out from eyes in excess amount so eyes become red due to
irritation. It is caused by a microbe Chlamydia trachomatis.
J. Photophobia: In this defect proper image is not formed in bright light.
TARGET POINTS
Dimlight vision – Scotopic vision
Bright light vision – Photopic vision.
The eyes of some animals shine at night, because in the eyes of these animals, there is a
pigment just outside the retina in the choroid layer of eyeball, which reflects the light rays
coming from retina. This layer is called Tapetum. Due to this layer, these animals are capable
to see in dark also.
Kangaroo, hoofed mammals, elephants, whales etc, are having a silver shining layer of fibrous
connective tissue called Tapetum fibrosum.
In elasmobranch fishes a reflecting color pigment called Guanine is present in tapetum layer
so it is called tapetum lucidum.
Hunters and carnivorous mammals like dogs, cats, tigers etc have a layer in their retina called
tapetum cellulosum.
In the eyes of birds pectin is found.
Emmetropia: Normal vision of eyes is called emmetropia.
Few more glands of eyes:
(i) Meibomian glands: These are present at inner surface of eyelids and secrete an oily substance,
which is scattered at the edges of eye lids. It prevent friction between two eye lids.
(ii) Gland of Zeis: It is situated in margin of eye lid.
(iii)Harderian glands: These are found inside the lower eye lids. These moisten the nictitating
membrane. Harderian glands are absent in rabbit and human. In pace of Harderian glands, in
mammals, Meibomian glands are present. But in some mammals eg. Rats, shrews, whales
etc. these Harderian glands are found. These glands are also found in frog and birds.
(iv) Gland of Moll: These are modified sweat gland found in the eye lashes.
F. Color blindness: it is genetic disorder of X chromosomes. It is due to recessive gene. Color
blind persons cannot differentiate in red and green color.
G. Cataract: In this defect, lens becomes more solid, brown or more flat. It occurs in old age mostly.
The lens become opaque, and reduces its power of accommodation. At this stage person cannot
see. A new lens is administered in place of defective lens by operation.
H. Glaucoma: If the canal of schlemm is blocked in eyeball, aqueous humour cannot return to veins
again as a pressure is increased in eye chambers ad retina is damaged and person becomes totally
blind.
I. Trachoma: A watery liquid oozes out from eyes in excess amount so eyes become red due to
irritation. It is caused by a microbe Chlamydia trachomatis.
J. Photophobia: In this defect proper image is not formed in bright light.
TARGET POINTS
Dimlight vision – Scotopic vision
Bright light vision – Photopic vision.
The eyes of some animals shine at night, because in the eyes of these animals, there is a
pigment just outside the retina in the choroid layer of eyeball, which reflects the light rays
coming from retina. This layer is called Tapetum. Due to this layer, these animals are capable
to see in dark also.
Kangaroo, hoofed mammals, elephants, whales etc, are having a silver shining layer of fibrous
connective tissue called Tapetum fibrosum.
In elasmobranch fishes a reflecting color pigment called Guanine is present in tapetum layer
so it is called tapetum lucidum.
Hunters and carnivorous mammals like dogs, cats, tigers etc have a layer in their retina called
tapetum cellulosum.
In the eyes of birds pectin is found.
Emmetropia: Normal vision of eyes is called emmetropia.
Few more glands of eyes:
(i) Meibomian glands: These are present at inner surface of eyelids and secrete an oily substance,
which is scattered at the edges of eye lids. It prevent friction between two eye lids.
(ii) Gland of Zeis: It is situated in margin of eye lid.
(iii)Harderian glands: These are found inside the lower eye lids. These moisten the nictitating
membrane. Harderian glands are absent in rabbit and human. In pace of Harderian glands, in
mammals, Meibomian glands are present. But in some mammals eg. Rats, shrews, whales
etc. these Harderian glands are found. These glands are also found in frog and birds.
(iv) Gland of Moll: These are modified sweat gland found in the eye lashes.
79
3.3 EAR
3.3.1 Structures and functions of the outer and middle ear
Hearing is the transduction of sound waves into a neural signal that relies on the structure of the ear.
The outwardly visible structure that is often referred to as the ear is more correctly referred to as the
outer ear (external ear), or the auricle. The C shaped of the auricle direct sound waves towards the
ear canal, which enters into the skull through the external auditory meatus of the temporal bone. At
the end of the ear canal is the tympanic membrane, or ear drum, which vibrates with the movement
of air in sound waves.
Along the length of the ear canal are ceruminous glands that contribute to the production of cerumen
(earwax). Because cerumen is sticky it can help prevent small particles from finding their way to the
tympanic membrane. Cerumen also helps prevent bacterial growth, waterproofs the auditory canal
and tympanic membrane, and may be as deterrent to small insects.
The middle ear consists of a space spanned by three small bones, the ossicles, which amplify the
movements of the tympanic membrane. These small bones are the malleus, incus, and stapes,
which are Latin names that roughly translate to hammer, anvil, and stirrup. The malleus is attached
to the tympanic membrane and articulates with the incus, which articulates with the stapes. The
stapes is then attached to the inner ear where the sound waves will be transduced to a neural
signal.
The middle ear is also connected to the pharynx through the auditory tube (Eustachian tube) that
helps equilibrate air pressure across the tympanic membrane. When flying, you may have experienced
what happens when the pressures across the tympanic membrane. When flying, you may have
experienced what happens when the pressures across the tympanic membrane are not equal. As
the plane climbs, pressure on the outside of the membrane decreases. If there is not a corresponding
decrease in pressure in the middle ear, the pressure difference will cause the eardrum to push
outward, causing pain and muffled hearing. The auditory tube is normally closed, but will typically
open when muscles of the pharynx contract during swallowing or yawning. Thus, chewing gum or
drinking as the plane climbs will often relieve these symptoms. The auditory tube also provides a
pathway of drainage for fluids that accumulate during middle ear infections (otitis media).
Unfortunately, it is also the auditory tubes that play a role in causing otitis media, as microorganisms
can use this path to move from the pharynx into the middle ear. This is especially common in
children.
3.3 EAR
3.3.1 Structures and functions of the outer and middle ear
Hearing is the transduction of sound waves into a neural signal that relies on the structure of the ear.
The outwardly visible structure that is often referred to as the ear is more correctly referred to as the
outer ear (external ear), or the auricle. The C shaped of the auricle direct sound waves towards the
ear canal, which enters into the skull through the external auditory meatus of the temporal bone. At
the end of the ear canal is the tympanic membrane, or ear drum, which vibrates with the movement
of air in sound waves.
Along the length of the ear canal are ceruminous glands that contribute to the production of cerumen
(earwax). Because cerumen is sticky it can help prevent small particles from finding their way to the
tympanic membrane. Cerumen also helps prevent bacterial growth, waterproofs the auditory canal
and tympanic membrane, and may be as deterrent to small insects.
The middle ear consists of a space spanned by three small bones, the ossicles, which amplify the
movements of the tympanic membrane. These small bones are the malleus, incus, and stapes,
which are Latin names that roughly translate to hammer, anvil, and stirrup. The malleus is attached
to the tympanic membrane and articulates with the incus, which articulates with the stapes. The
stapes is then attached to the inner ear where the sound waves will be transduced to a neural
signal.
The middle ear is also connected to the pharynx through the auditory tube (Eustachian tube) that
helps equilibrate air pressure across the tympanic membrane. When flying, you may have experienced
what happens when the pressures across the tympanic membrane. When flying, you may have
experienced what happens when the pressures across the tympanic membrane are not equal. As
the plane climbs, pressure on the outside of the membrane decreases. If there is not a corresponding
decrease in pressure in the middle ear, the pressure difference will cause the eardrum to push
outward, causing pain and muffled hearing. The auditory tube is normally closed, but will typically
open when muscles of the pharynx contract during swallowing or yawning. Thus, chewing gum or
drinking as the plane climbs will often relieve these symptoms. The auditory tube also provides a
pathway of drainage for fluids that accumulate during middle ear infections (otitis media).
Unfortunately, it is also the auditory tubes that play a role in causing otitis media, as microorganisms
can use this path to move from the pharynx into the middle ear. This is especially common in
children.
80
Helix
Auricle
Tympanic
membrane
Auditory
canal
Lobule
Auditory tube
Tensor tympani
muscle
Tympanic cavity
Round window
Cochlea
Vestibule
Cochlear nerve
Vestibular nerve
Oval window
Semicircular ducts
Ossicles:
Stapes
Incus
Malleus
Outer ear Inner earMiddle ear
Anatomy of the Ear
3.3.2 Structure and function of the inner ear
The inner ear is entirely enclosed within the temporal bone, it has two separate regions, the cochlea
and vestibule, which are responsible for hearing and balance, respectively. The neural signals
from the two regions of the inner ear are relayed to the brainstem through separate fibre bundles,
but which run together as the vestibulo cochlear nerve.
Sound information is transmitted from the middle ear to the inner ear via the stapes attachment to
the oval window, which is a membrane at the beginning of the cochlea. As the tympanic membrane
vibrates from sound waves, the ossicles amplify that vibration, and then the oval window moves
with the same vibrations. The oval window is at the beginning of a tube that runs the length of the
cochlea to its tip (helicotrema)and back alongside itself to end at another membrane called the
round window (secondary tympanic membrane).
Tympanic membrane
(vibrating)
Stapes footplate vibrating
the oval window
Scala vestibuli
Scala tympani
Cochlear duct
HelicotremaBasilar membrane (vibrating)
Round window vibrating in response to fluid vibrations
a) Simplified anatomy of the cochlea
Helix
Auricle
Tympanic
membrane
Auditory
canal
Lobule
Auditory tube
Tensor tympani
muscle
Tympanic cavity
Round window
Cochlea
Vestibule
Cochlear nerve
Vestibular nerve
Oval window
Semicircular ducts
Ossicles:
Stapes
Incus
Malleus
Outer ear Inner earMiddle ear
Anatomy of the Ear
3.3.2 Structure and function of the inner ear
The inner ear is entirely enclosed within the temporal bone, it has two separate regions, the cochlea
and vestibule, which are responsible for hearing and balance, respectively. The neural signals
from the two regions of the inner ear are relayed to the brainstem through separate fibre bundles,
but which run together as the vestibulo cochlear nerve.
Sound information is transmitted from the middle ear to the inner ear via the stapes attachment to
the oval window, which is a membrane at the beginning of the cochlea. As the tympanic membrane
vibrates from sound waves, the ossicles amplify that vibration, and then the oval window moves
with the same vibrations. The oval window is at the beginning of a tube that runs the length of the
cochlea to its tip (helicotrema)and back alongside itself to end at another membrane called the
round window (secondary tympanic membrane).
Tympanic membrane
(vibrating)
Stapes footplate vibrating
the oval window
Scala vestibuli
Scala tympani
Cochlear duct
HelicotremaBasilar membrane (vibrating)
Round window vibrating in response to fluid vibrations
a) Simplified anatomy of the cochlea
81
Pure
tone
Cochlear partition (cochlear
duct and basilar membrane)
Air
Base Round window Fluid Apex
Oval
window
b) Sound wave transmitted into the cochlea
As the oval window is pushed in by sound waves, fluid within this tube is pushed along its length and
the round window at its other end can bulge out as a result of that movement. Likewise, when the
oval window is pulled back, the fluid inside this tube is drawn back and the round window can pucker
in to compensate. As vibrations of the tympanic membrane are transmitted through the ossicles, a
wave (often referred to as standing wave because of its properties) is created within the fluid in the
cochlea that displaces sections of the Cochlear partition (cochlear duct and basilar membrane).
It is these waves that are detected by the sensing cells found attached to the basilar membrane.
The tube running from the oval to the round window in the cochlea is separated into two spaces.
From the oval window to the tip of the cochlea the tube is referred to as the scala vestibule and
from the tip of the cochlea back to the round window it is the scala tympani. These spaces can be
seen in a cross section of one turn of the cochlea.
The two spaces are on either side of the cochlear duct, which is the space that contains the
structures that transduce sound into the neural signal. Those structures are contained within the
spiral organ or organ of corti, which lies on top of the basilar membrane that separates it from
the scala tympani. The spiral organ contains hair cells with stereocilia on their apical membrane.
The stereocilia bend in response to movement of the basilar membrane relative to the partially fixed
tectorial membrane. Depending on which direction the stereocilia bend, they open or close ion
channels, leading to signal changes in the cochlear nerve.
As a standing wave is set up within the scala vestibuli and scala tympani in response to movement
at the oval window, the basilar membrane responds by moving at a specific spot, dependent on the
frequency of the standing wave.
Pure
tone
Cochlear partition (cochlear
duct and basilar membrane)
Air
Base Round window Fluid Apex
Oval
window
b) Sound wave transmitted into the cochlea
As the oval window is pushed in by sound waves, fluid within this tube is pushed along its length and
the round window at its other end can bulge out as a result of that movement. Likewise, when the
oval window is pulled back, the fluid inside this tube is drawn back and the round window can pucker
in to compensate. As vibrations of the tympanic membrane are transmitted through the ossicles, a
wave (often referred to as standing wave because of its properties) is created within the fluid in the
cochlea that displaces sections of the Cochlear partition (cochlear duct and basilar membrane).
It is these waves that are detected by the sensing cells found attached to the basilar membrane.
The tube running from the oval to the round window in the cochlea is separated into two spaces.
From the oval window to the tip of the cochlea the tube is referred to as the scala vestibule and
from the tip of the cochlea back to the round window it is the scala tympani. These spaces can be
seen in a cross section of one turn of the cochlea.
The two spaces are on either side of the cochlear duct, which is the space that contains the
structures that transduce sound into the neural signal. Those structures are contained within the
spiral organ or organ of corti, which lies on top of the basilar membrane that separates it from
the scala tympani. The spiral organ contains hair cells with stereocilia on their apical membrane.
The stereocilia bend in response to movement of the basilar membrane relative to the partially fixed
tectorial membrane. Depending on which direction the stereocilia bend, they open or close ion
channels, leading to signal changes in the cochlear nerve.
As a standing wave is set up within the scala vestibuli and scala tympani in response to movement
at the oval window, the basilar membrane responds by moving at a specific spot, dependent on the
frequency of the standing wave.
82
Oval window
Vestibular
membrane
Cochlear duct
(scala media)
Cochlear nerve
Tectorial
membrane
Hairs
(stereocilia)
Outer
hair cells
Supporting
cells
Basilar
membrane
Fibers of
cochlear
nerve
Inner hair
cell
Scala tympani
(with perilymph)
Spiral
ganglion
Scala vestibuli
(with perilymph)
Vestibular membrane
Cochlear duct (with
endolympy)
Tectorial membrane
Spiral organ
Basilar membrane
Cochlea is a spiral structure (a) divided into three chambers. (b) Middle chamber, cochlear
duct, contains the spiral organ that has hair cells (c) for sensing the vibrations we perceive
as sound.
Low-frequcncy sound
(20-800Hz)
Medium-frequcncy sound
(1,500-4,000Hz)
High-frequcncy sound
(7,000-20,000Hz)
Distal
end
(free)
Proximal end
(attached)
20,000 5,000 1,000 500 200 Hz
Different frequencies are sensed in different regions of the cochlea. High frequencies (high
pitch) are sensed near the base of the cochlea, whereas low frequencies are sensed near the
tip of the cochlea.
The cochlea encodes auditory stimuli based on frequency between 20 Hz and 20,000 Hz, the range
of human hearing. Higher frequencies (higher pitch) cause the basilar membrane close to the base
of the cochlea to move and lower frequencies (lower pitch) cause the basilar membrane closer to
the tip of the cochlea to move. Loudness or sound intensity is determined by the number of hair cells
in an area that are stimulated. A louder sound produces greater displacement of the basilar membrane,
leading to a greater number of stereocilia responding.
Oval window
Vestibular
membrane
Cochlear duct
(scala media)
Cochlear nerve
Tectorial
membrane
Hairs
(stereocilia)
Outer
hair cells
Supporting
cells
Basilar
membrane
Fibers of
cochlear
nerve
Inner hair
cell
Scala tympani
(with perilymph)
Spiral
ganglion
Scala vestibuli
(with perilymph)
Vestibular membrane
Cochlear duct (with
endolympy)
Tectorial membrane
Spiral organ
Basilar membrane
Cochlea is a spiral structure (a) divided into three chambers. (b) Middle chamber, cochlear
duct, contains the spiral organ that has hair cells (c) for sensing the vibrations we perceive
as sound.
Low-frequcncy sound
(20-800Hz)
Medium-frequcncy sound
(1,500-4,000Hz)
High-frequcncy sound
(7,000-20,000Hz)
Distal
end
(free)
Proximal end
(attached)
20,000 5,000 1,000 500 200 Hz
Different frequencies are sensed in different regions of the cochlea. High frequencies (high
pitch) are sensed near the base of the cochlea, whereas low frequencies are sensed near the
tip of the cochlea.
The cochlea encodes auditory stimuli based on frequency between 20 Hz and 20,000 Hz, the range
of human hearing. Higher frequencies (higher pitch) cause the basilar membrane close to the base
of the cochlea to move and lower frequencies (lower pitch) cause the basilar membrane closer to
the tip of the cochlea to move. Loudness or sound intensity is determined by the number of hair cells
in an area that are stimulated. A louder sound produces greater displacement of the basilar membrane,
leading to a greater number of stereocilia responding.
83
The information sensed by the spiral organ of the cochlea is transmitted into the brain via the
vestibulocochlear nerve (cranial nerve VIII) to nuclei in the pons. At the level of the pons and related
connections in the midbrain, some processing of auditory information occurs, including identifying
where a sound is coming from and responding to loud noises. From the pons and midbrain, fibers
carrying auditory information project to the thalamus and then, from there to the primary auditory
cortex of the temporal lobe. It is here that the conscious perception of sound is located.
Maculae and dynamic equilibrium
Along with hearing, the inner ear is responsible for encoding information about equilibrium (the
sense of balance), which it does in the vestibular apparatus.
Similar to the cochlea, the vestibular structures use hair cells with stereocilia to detect movement of
fluid in this case, in response to changes in head position or acceleration. Detection of head position
when the body is stationary is termed static equilibrium. The information for static equilibrium
comes from the utricle and saccule. Dynamic equilibrium is the perception of acceleration.
Information for dynamic equilibrium can come from the utricle and saccule, which detect linear
acceleration, and/or the semi-circular canals, which detect angular acceleration. The neural signals
generated from the vestibule are transmitted to the brainstem and cerebellum from sensory neurons
in the vestibular ganglion.
The saccule and utricle each contain a sense organ, called the macula, where stereocilia and their
supporting cells are found. These maculae (plural) are oriented 90 degrees to one another so that
they respond to positions in different planes.
Superior
Vestibular apparatus
Endolymphatic sac
Semicircular ducts
Anterior
Posterior
Lateral
Ampullae
UtricleSaccule
Cochlea
Spiral ganglion of cochlea
Cochlear nerve
Vestibular ganglia
Vestibular nerve
The organs can respond to changes in position and acceleration because the tips of their stereocilia
project into a dense otolithic membrane made up of a mixture containing granules of calcium and
protein, called otoliths, which gives rise to their common name, the otolithic organs. When the
maculae (otolithic organs) move, gravity causes the dense otolithic membrane to move relative to
the less dense cell layer beneath the stereocilia. This causes the stereocilia to bend, initiating action
potentials in the vestibular nerve fibers that innervate them.
The information sensed by the spiral organ of the cochlea is transmitted into the brain via the
vestibulocochlear nerve (cranial nerve VIII) to nuclei in the pons. At the level of the pons and related
connections in the midbrain, some processing of auditory information occurs, including identifying
where a sound is coming from and responding to loud noises. From the pons and midbrain, fibers
carrying auditory information project to the thalamus and then, from there to the primary auditory
cortex of the temporal lobe. It is here that the conscious perception of sound is located.
Maculae and dynamic equilibrium
Along with hearing, the inner ear is responsible for encoding information about equilibrium (the
sense of balance), which it does in the vestibular apparatus.
Similar to the cochlea, the vestibular structures use hair cells with stereocilia to detect movement of
fluid in this case, in response to changes in head position or acceleration. Detection of head position
when the body is stationary is termed static equilibrium. The information for static equilibrium
comes from the utricle and saccule. Dynamic equilibrium is the perception of acceleration.
Information for dynamic equilibrium can come from the utricle and saccule, which detect linear
acceleration, and/or the semi-circular canals, which detect angular acceleration. The neural signals
generated from the vestibule are transmitted to the brainstem and cerebellum from sensory neurons
in the vestibular ganglion.
The saccule and utricle each contain a sense organ, called the macula, where stereocilia and their
supporting cells are found. These maculae (plural) are oriented 90 degrees to one another so that
they respond to positions in different planes.
Superior
Vestibular apparatus
Endolymphatic sac
Semicircular ducts
Anterior
Posterior
Lateral
Ampullae
UtricleSaccule
Cochlea
Spiral ganglion of cochlea
Cochlear nerve
Vestibular ganglia
Vestibular nerve
The organs can respond to changes in position and acceleration because the tips of their stereocilia
project into a dense otolithic membrane made up of a mixture containing granules of calcium and
protein, called otoliths, which gives rise to their common name, the otolithic organs. When the
maculae (otolithic organs) move, gravity causes the dense otolithic membrane to move relative to
the less dense cell layer beneath the stereocilia. This causes the stereocilia to bend, initiating action
potentials in the vestibular nerve fibers that innervate them.
Bundles of stereocilia are arranged in various directions, so that any direction of inclination will
depolarize a subset of the hair cells and hyperpolarize a corresponding subset of sensory neurons.
How the body senses head position and the linear (horizontal or vertical) direction of acceleration is
determined by the specific pattern of hair cell activity across the maculae.
Macula sacculi
Stereocilia of hair cells bend
Otolithic membrane sags
Gravitational force
Otoliths
Otolithic
membrane
Supporting cell
Hair cell
Vestibular nerve
Crista ampullaris and dynamic equilibrium
The semi-circular canals are three ring like extensions from the vestibule (the region containing the
saccule and utricle). One is oriented in the horizontal plane and two are in the vertical plane. The
vertical canals are 45
0
off of the sagittal plane, one is anterior and one is posterior.
At the base of each semi-circular canal where it meets with the vestibule is an enlarged region
known as the ampulla, which contains a hair cell containing structure, called the crista ampullaris
that responds to rotational movement. The stereocilia of the hair cells extend into the cupula, a
membrane tat attaches to the top of the ampulla.
When the head rotates in a plane parallel to the semi – circular canal, the fluid in the canal does not
move as quickly as the head is moving. This pushes the cupula in the opposite direction, deflecting
the stereocilia and creating a nerve impulse. Considering the semi-circular canals on either side of
the head, three orthogonal planes are defined, the horizontal plane with both horizontal canals, and
two vertical planes 90 degree to each other with the anterior canal from one side and the posterior
canal from the other. In each pair, deflection of the cupula on one side of the body causes
depolarization of the hair cells while the same movement causes hyperpolarization of the hair cells
on the other side of the body. For example, when the head rotates to the right, the horizontal canals
are active and the right side depolarizes while the left hyperpolarizes, indicating the direction of the
movement. By comparing the relative movements of all six semi – circular canals, the vestibular
system can establish movement in any direction within 3D space.
Informative from the vestibular apparatus projects to a wide range of structures in the brain. The
information enters the brain via the vestibulocochlear nerve (cranial nerve VIII) where it synapses
at
depolarize a subset of the hair cells and hyperpolarize a corresponding subset of sensory neurons.
How the body senses head position and the linear (horizontal or vertical) direction of acceleration is
determined by the specific pattern of hair cell activity across the maculae.
Macula sacculi
Stereocilia of hair cells bend
Otolithic membrane sags
Gravitational force
Otoliths
Otolithic
membrane
Supporting cell
Hair cell
Vestibular nerve
Crista ampullaris and dynamic equilibrium
The semi-circular canals are three ring like extensions from the vestibule (the region containing the
saccule and utricle). One is oriented in the horizontal plane and two are in the vertical plane. The
vertical canals are 45
0
off of the sagittal plane, one is anterior and one is posterior.
At the base of each semi-circular canal where it meets with the vestibule is an enlarged region
known as the ampulla, which contains a hair cell containing structure, called the crista ampullaris
that responds to rotational movement. The stereocilia of the hair cells extend into the cupula, a
membrane tat attaches to the top of the ampulla.
When the head rotates in a plane parallel to the semi – circular canal, the fluid in the canal does not
move as quickly as the head is moving. This pushes the cupula in the opposite direction, deflecting
the stereocilia and creating a nerve impulse. Considering the semi-circular canals on either side of
the head, three orthogonal planes are defined, the horizontal plane with both horizontal canals, and
two vertical planes 90 degree to each other with the anterior canal from one side and the posterior
canal from the other. In each pair, deflection of the cupula on one side of the body causes
depolarization of the hair cells while the same movement causes hyperpolarization of the hair cells
on the other side of the body. For example, when the head rotates to the right, the horizontal canals
are active and the right side depolarizes while the left hyperpolarizes, indicating the direction of the
movement. By comparing the relative movements of all six semi – circular canals, the vestibular
system can establish movement in any direction within 3D space.
Informative from the vestibular apparatus projects to a wide range of structures in the brain. The
information enters the brain via the vestibulocochlear nerve (cranial nerve VIII) where it synapses
at
vestibular nuclei in the pons and medulla. From here, information travels to a number of other
regions to stimulate reflexes and develop our conscious awareness of position and movement.
Semicircular ducts:
Anterior
Lateral
Posterior
Ampullae
Cupula
Endolymph
Hair cells
Supporting cells
Sensory nerve fibers
Endolymph
lags behind
due to inertia Stereocilia are bent
Direction of head rotation
Cupula is pushed
over and
stimulates
hair cells
Crista ampullaris
Crista ampullaris and cupula
3.4 TASTE (GUSTATION)
Taste buds are numerous in the circumvallate and foliate papillae. Taste buds are formed by the
transformation of epithelial cells of the tongue and bud possesses two types of cells:
A. Supporting cells: These cells are elongated in middle region. They do not bear sensory hairs at
their free ends.
B. Sensory cells: These cells are elongated
buldge in middle part, they bear sensory hair
at their free ends. Each taste bud is flask or
barrel shaped. Its upper part opens at the
epithelial surface of the tongue through a
fine pore. These sensory hairs, exposed to
outside through the gustatory pore areSensory
nerve fibers
Basal cell
stimulated by the food substances. The Taste bud
sensory cells are chemoreceptor in nature and taste the food while it is dissolved in saliva. Food
substances get mixed with saliva to enter into the pores of taste buds.
3.5 SMELL (OLFACTION)
Olfactoreceptors
Olfactoreceptors are situated in the upper part of nasal chamber in olfactory epithelium. This
membrane is called as schnederian membrane. Olfactoreceptors are related with olfactory bulb. It
Supporting
cell
Taste cell
Taste pore
Taste hairs
Tongue
epithelium
regions to stimulate reflexes and develop our conscious awareness of position and movement.
Semicircular ducts:
Anterior
Lateral
Posterior
Ampullae
Cupula
Endolymph
Hair cells
Supporting cells
Sensory nerve fibers
Endolymph
lags behind
due to inertia Stereocilia are bent
Direction of head rotation
Cupula is pushed
over and
stimulates
hair cells
Crista ampullaris
Crista ampullaris and cupula
3.4 TASTE (GUSTATION)
Taste buds are numerous in the circumvallate and foliate papillae. Taste buds are formed by the
transformation of epithelial cells of the tongue and bud possesses two types of cells:
A. Supporting cells: These cells are elongated in middle region. They do not bear sensory hairs at
their free ends.
B. Sensory cells: These cells are elongated
buldge in middle part, they bear sensory hair
at their free ends. Each taste bud is flask or
barrel shaped. Its upper part opens at the
epithelial surface of the tongue through a
fine pore. These sensory hairs, exposed to
outside through the gustatory pore areSensory
nerve fibers
Basal cell
stimulated by the food substances. The Taste bud
sensory cells are chemoreceptor in nature and taste the food while it is dissolved in saliva. Food
substances get mixed with saliva to enter into the pores of taste buds.
3.5 SMELL (OLFACTION)
Olfactoreceptors
Olfactoreceptors are situated in the upper part of nasal chamber in olfactory epithelium. This
membrane is called as schnederian membrane. Olfactoreceptors are related with olfactory bulb. It
Supporting
cell
Taste cell
Taste pore
Taste hairs
Tongue
epithelium
86
is the extension of limbic system. This bulb is situated below the frontal lobe of cerebral hemisphere
and above the ethmoid bone of nasal chamber.
Three types of cells are found in the olfactoreceptors.
A. Bipolar olfactory nerve cells: Special types of nerve cells with sensory hairs at the anterior end
of olfactory cells. They contact with external environment in nasal chamber. Sensory hairs are related
with dendrites of bipolar nerve cells. Middle part of olfactory cell is cyton. Posterior part of olfactory
cell is axon which is non myelinated.
B. Columnar epithelial cells: Also called as supporting cells, present around the bipolar olfactory
cells. They provide support to the olfactory cells. Some small conical cells are also found at the
basal part of olfactoreceptors and provide base to the olfactoreceptors. A layer of connective tissue
lies below the olfactoreceptors. It is also called as lamina propria.
C. Mucous glands (Bowman’s gland): Situated in the Lamina propria, opens at the outer part of
olfacto receptor through fine duct. Their secretory mucous substances dissolve the smell particles
and carry to the sensory hair of olfactory cells. Non myelinated axons of all olfacto sensory cells
makes the synapse with dendrites of multipolar neurons of olfactory bulb. The number of receptors
stimulated indicates the strength of smell.
In addition to smell receptors, a network of nerves is found in the nose, mouth and tongue. The
network formed by the trigeminal nerve of V cranial nerve. It is also known as Dentist’s nerve, reacts
to messages of pain of teeth. It also conveys the message of smell to brain. Such as ammonia,
vinegar etc. The trigeminal can protect by warning about harmful chemical in the air. Bowman’s glands
present inside the nose releases mucous to get rid of the irritating substances. Loss of the sense of
smell is known as anosmia. It occurs due to congenital abnormalities of olfactory bulbs or nerves.
Frontal lobe of cerebrum
Cribriform palte
of ethmoid bone
Olfactory bulb
Cribriform plate of
ethmoid bone
Olfactory (I) nefve fibre
Lamina propria
Supporting cell
Olfactory cell
Olfactory hairs
(dendrites)
Substance being smelled
Olfactory tract
Olfactory bulb
Olfactory (I)
nerves (receptor)
Olfactory epithelium
Superior nasal concha
Middle nasal concha
Olfactory tract
is the extension of limbic system. This bulb is situated below the frontal lobe of cerebral hemisphere
and above the ethmoid bone of nasal chamber.
Three types of cells are found in the olfactoreceptors.
A. Bipolar olfactory nerve cells: Special types of nerve cells with sensory hairs at the anterior end
of olfactory cells. They contact with external environment in nasal chamber. Sensory hairs are related
with dendrites of bipolar nerve cells. Middle part of olfactory cell is cyton. Posterior part of olfactory
cell is axon which is non myelinated.
B. Columnar epithelial cells: Also called as supporting cells, present around the bipolar olfactory
cells. They provide support to the olfactory cells. Some small conical cells are also found at the
basal part of olfactoreceptors and provide base to the olfactoreceptors. A layer of connective tissue
lies below the olfactoreceptors. It is also called as lamina propria.
C. Mucous glands (Bowman’s gland): Situated in the Lamina propria, opens at the outer part of
olfacto receptor through fine duct. Their secretory mucous substances dissolve the smell particles
and carry to the sensory hair of olfactory cells. Non myelinated axons of all olfacto sensory cells
makes the synapse with dendrites of multipolar neurons of olfactory bulb. The number of receptors
stimulated indicates the strength of smell.
In addition to smell receptors, a network of nerves is found in the nose, mouth and tongue. The
network formed by the trigeminal nerve of V cranial nerve. It is also known as Dentist’s nerve, reacts
to messages of pain of teeth. It also conveys the message of smell to brain. Such as ammonia,
vinegar etc. The trigeminal can protect by warning about harmful chemical in the air. Bowman’s glands
present inside the nose releases mucous to get rid of the irritating substances. Loss of the sense of
smell is known as anosmia. It occurs due to congenital abnormalities of olfactory bulbs or nerves.
Frontal lobe of cerebrum
Cribriform palte
of ethmoid bone
Olfactory bulb
Cribriform plate of
ethmoid bone
Olfactory (I) nefve fibre
Lamina propria
Supporting cell
Olfactory cell
Olfactory hairs
(dendrites)
Substance being smelled
Olfactory tract
Olfactory bulb
Olfactory (I)
nerves (receptor)
Olfactory epithelium
Superior nasal concha
Middle nasal concha
Olfactory tract
87
TARGET NOTES
Differences of receptors between rabbit and man
Minimum distance for proper vision of eyes is 25 cm. Anterior posterior diameter of eyeball is
17.5 mm at the time of birth, normally and in adults it is 20 to 21 mm. The lens of man’s eye ball
has its diameter of 11 mm. In a newly born child, eye balls are very small i.e. babies are always
very much hypermatropic.
The best colour differentiation is found in primates (advanced mammals). In the retina of man’s
eyes there are found 1110 – 1125 lacs rods and 65 lacs cones. Healthy eye of a person can see
clearly from 12 inch to 20 feet. Image of object is formed on retina and it is always inverted and
real. Eyes are most sensitive to the light having approx. 5000 Å wavelength.
Hyalocytes cells are found in vitreous humour. Ciliary body secretes aqueous humour and
vitreous humour.
In frog and other amphibians sclera is cartilaginous. Frog’s vision is hypermatropic in water
and myopic on land.
The largest eyes are found in deers in vertebrates with respect to body surface area.
Atropine, beladona and cocaine medicines are used to dilate the pupil.
Cornea and lens of eye lack blood supply
Light sensitive organ was discovered by Steven.
Stye is infection of gland of zeis.
The relationship of receptor to bipolar cells to ganglion cells is 1:1:1 within the fovea from the
fovea to the periphery, cones diminish and rods increase in number. Electrical activity of retina
is record in sequence of potential change known as electroretinogram.
The horizontal cells which transmit signals horizontally in the outer plexiform layer from the
rods and cones to the bipolar cell dendrites. The bipolar cells which transmit signals from the
rods, cones and horizontal cells to the inner plexiform layer where they synapse with ganglion
cell and amacrine cells. The amacrine cells which transmit signals in two directions directly
from bipolar cells to ganglion.
Internal or inner ear of rabbit is originated by ectoderm of embryo and middle ear (bony part
mesodermal) and Eustachian tube are originated by endoderm layer of embryo.
Rabbit Man
EYE: Monocular vision, Both eyes are locatedEYE: Binocular vision, Both eye are located
on the dorsal and lateral side of head, red in at anterior part of face, black, blue, brown in
color and nictitating membrane is present. color and nictitating membrane is vestigial
which is called as plica semilunaris.
EAR: Ear pinna is funnel shaped, motile andEAR: Ear pinna is kidney shaped, non-motile
no. of coiling of cochlear canal is 2 ½ and no. of coiling of cochlear canal is 2 ¾ .
TARGET NOTES
Differences of receptors between rabbit and man
Minimum distance for proper vision of eyes is 25 cm. Anterior posterior diameter of eyeball is
17.5 mm at the time of birth, normally and in adults it is 20 to 21 mm. The lens of man’s eye ball
has its diameter of 11 mm. In a newly born child, eye balls are very small i.e. babies are always
very much hypermatropic.
The best colour differentiation is found in primates (advanced mammals). In the retina of man’s
eyes there are found 1110 – 1125 lacs rods and 65 lacs cones. Healthy eye of a person can see
clearly from 12 inch to 20 feet. Image of object is formed on retina and it is always inverted and
real. Eyes are most sensitive to the light having approx. 5000 Å wavelength.
Hyalocytes cells are found in vitreous humour. Ciliary body secretes aqueous humour and
vitreous humour.
In frog and other amphibians sclera is cartilaginous. Frog’s vision is hypermatropic in water
and myopic on land.
The largest eyes are found in deers in vertebrates with respect to body surface area.
Atropine, beladona and cocaine medicines are used to dilate the pupil.
Cornea and lens of eye lack blood supply
Light sensitive organ was discovered by Steven.
Stye is infection of gland of zeis.
The relationship of receptor to bipolar cells to ganglion cells is 1:1:1 within the fovea from the
fovea to the periphery, cones diminish and rods increase in number. Electrical activity of retina
is record in sequence of potential change known as electroretinogram.
The horizontal cells which transmit signals horizontally in the outer plexiform layer from the
rods and cones to the bipolar cell dendrites. The bipolar cells which transmit signals from the
rods, cones and horizontal cells to the inner plexiform layer where they synapse with ganglion
cell and amacrine cells. The amacrine cells which transmit signals in two directions directly
from bipolar cells to ganglion.
Internal or inner ear of rabbit is originated by ectoderm of embryo and middle ear (bony part
mesodermal) and Eustachian tube are originated by endoderm layer of embryo.
Rabbit Man
EYE: Monocular vision, Both eyes are locatedEYE: Binocular vision, Both eye are located
on the dorsal and lateral side of head, red in at anterior part of face, black, blue, brown in
color and nictitating membrane is present. color and nictitating membrane is vestigial
which is called as plica semilunaris.
EAR: Ear pinna is funnel shaped, motile andEAR: Ear pinna is kidney shaped, non-motile
no. of coiling of cochlear canal is 2 ½ and no. of coiling of cochlear canal is 2 ¾ .
88
1. Damage to hearing is caused by sound
which exceeds
a) 70 decibels b) 100 decibels
c) 110 decibels d) 120 decibels
2. Gustatoreceptors are
a) Rod cells of eyes
b) Taste buds of tongue
c) Epithelium of skin
d) Cone cells of eyes
3. If the light source in front of an eye becomes
bright suddenly
a) Focus of lens will change
b) Retinal blood supply is cut
c) Vitreous humour becomes fluid
d) Pupil will contract
4. Aperture of pupil is controlled by
a) Conjunctiva b) Cornea
c) Iris d) Retina
5. Centre for sense of smell is
a) Cerebellum b) Olfactory lobes
c) Hind brain d) Midbrain
6. Cavity of aqueous humour is
a) Behind the lens
b) In front of lens
c) Between choroid and sclerotic
d) None of these
7. The cornea is very important component of
the human eye. The main function of the
cornea is to
a) Bend the light before it reaches the lens
b) Provide structural support to the eye
c) Contain concentrated amount of cone
cells in the correct orientation
d) Change the shape of the lens to enable
the image to be focused on the retina
Simple Questions
8. Sight of delicious food usually makes mouth
watery, it is a
a) Hormonal respons
b) Neural response
c) Optic response
d) Olfactory response
9. Malleus, incus and stapes the three ear
ossicles are derived respectively from which
of the following jaw bones
a) Articular, quadrate and hyomandibular
b) Hyomandibular, quadrate and articular
c) Quadrate, articular and hyomandibular
d) Humerus, articular and squamosal
10. The membranous labyrinth is concerned
with
a) Hearing b) Equilibrium
c) Both (a) and (b) d) None of these
11. The pigment that helps eye to see in dim
light is
a) Iodopsin b) Rhodopsin
c) Haemocyanin d) Haematin
12. Myopia is a defect in human eyes in which
the image is formed
a) Behind retina and can be corrected by
using convex lens.
b) Behind retina and can be corrected by
using concave lens.
c) In front of retina and can be corrected
by using concave lens.
d) In front of retina and can be corrected
by using convex lens
13. Vestibule is constituted by
a) Semi circular canals and utriculus
b) Sacculus and utriculus
c) Sacculus and ampullae
d) Ampullae and lagena.
1. Damage to hearing is caused by sound
which exceeds
a) 70 decibels b) 100 decibels
c) 110 decibels d) 120 decibels
2. Gustatoreceptors are
a) Rod cells of eyes
b) Taste buds of tongue
c) Epithelium of skin
d) Cone cells of eyes
3. If the light source in front of an eye becomes
bright suddenly
a) Focus of lens will change
b) Retinal blood supply is cut
c) Vitreous humour becomes fluid
d) Pupil will contract
4. Aperture of pupil is controlled by
a) Conjunctiva b) Cornea
c) Iris d) Retina
5. Centre for sense of smell is
a) Cerebellum b) Olfactory lobes
c) Hind brain d) Midbrain
6. Cavity of aqueous humour is
a) Behind the lens
b) In front of lens
c) Between choroid and sclerotic
d) None of these
7. The cornea is very important component of
the human eye. The main function of the
cornea is to
a) Bend the light before it reaches the lens
b) Provide structural support to the eye
c) Contain concentrated amount of cone
cells in the correct orientation
d) Change the shape of the lens to enable
the image to be focused on the retina
Simple Questions
8. Sight of delicious food usually makes mouth
watery, it is a
a) Hormonal respons
b) Neural response
c) Optic response
d) Olfactory response
9. Malleus, incus and stapes the three ear
ossicles are derived respectively from which
of the following jaw bones
a) Articular, quadrate and hyomandibular
b) Hyomandibular, quadrate and articular
c) Quadrate, articular and hyomandibular
d) Humerus, articular and squamosal
10. The membranous labyrinth is concerned
with
a) Hearing b) Equilibrium
c) Both (a) and (b) d) None of these
11. The pigment that helps eye to see in dim
light is
a) Iodopsin b) Rhodopsin
c) Haemocyanin d) Haematin
12. Myopia is a defect in human eyes in which
the image is formed
a) Behind retina and can be corrected by
using convex lens.
b) Behind retina and can be corrected by
using concave lens.
c) In front of retina and can be corrected
by using concave lens.
d) In front of retina and can be corrected
by using convex lens
13. Vestibule is constituted by
a) Semi circular canals and utriculus
b) Sacculus and utriculus
c) Sacculus and ampullae
d) Ampullae and lagena.
89
14. Eustachian canal connects
a) Middle ear with external ear
b) Middle ear with internal ear
c) External ear with internal ear
d) Pharynx with middle ear
15. Statoreceptors are located in
a) Cristae b) Maculae
c) Both (a) and (b) d) Cochlea
16. Which of the following is the correct
sequence for passage of sensory impulses
through the cells of the retina?
a) Ganglion neurons, rods and cones,
bipolar neurons
b) Rods and cones, bipolar neurons,
ganglion neurons
c) Rods and cones, ganglion neurons,
bipolar neurons
d) Ganglion neurons, bipolar neurons, rods
and cones
17. Receptor cells for balancing occur in human
ear in
a) Malleus, incus and stapes
b) Utriculus, sacculus and semi-circular
canals
c) Organ of corti
d) Eustachian tube
18. The receptors found in the muscles,
tendons and joints are
a) Teloreceptors b) Proprioceptors
c) Interoceptors d) Thermoreceptors
19. The exposed transparent region of eye ball
represents
a) Uvea
b) Cornea and conjunctiva
c) Fibrous coat
d) Iris
20. Myopia can be corrected by
a) Cylindrical lens
b) Bifocal lens
c) Biconvex lens
d) Biconcave lens
21. The other name of internal ear is
a) Utriculus
b) Membranous labyrinth
c) Sacculus
d) Ductus endolymphaticus
22. Color to the eye is imparted by
a) Lens b) Pupil
c) Iris d) Vitreous humour
23. Receptors for initial contact and movement
of object over the skin are
a) Pacinian corpuscles
b) Hair end organs
c) Merkel’s discs
d) Ruffini’s corpuscles
24. The order of the three layers of cells in the
retina of human eye from inside to outside
is
a) Bipolar cells, photoreceptor cells,
ganglion cells
b) Ganglion cells, rods, cones
c) Ganglion cells, bipolar cells,
photoreceptor cells
d) Photoreceptor cells, ganglion cells,
bipolar cells
25. In the central region of the retina, there is a
yellowish spot, the macula lutea, with a
depression in its centre that produces the
sharpest vision. This depression is called
a) Optic disc b) Rods and cones
c) Vitreous body d) Fovea centralis
14. Eustachian canal connects
a) Middle ear with external ear
b) Middle ear with internal ear
c) External ear with internal ear
d) Pharynx with middle ear
15. Statoreceptors are located in
a) Cristae b) Maculae
c) Both (a) and (b) d) Cochlea
16. Which of the following is the correct
sequence for passage of sensory impulses
through the cells of the retina?
a) Ganglion neurons, rods and cones,
bipolar neurons
b) Rods and cones, bipolar neurons,
ganglion neurons
c) Rods and cones, ganglion neurons,
bipolar neurons
d) Ganglion neurons, bipolar neurons, rods
and cones
17. Receptor cells for balancing occur in human
ear in
a) Malleus, incus and stapes
b) Utriculus, sacculus and semi-circular
canals
c) Organ of corti
d) Eustachian tube
18. The receptors found in the muscles,
tendons and joints are
a) Teloreceptors b) Proprioceptors
c) Interoceptors d) Thermoreceptors
19. The exposed transparent region of eye ball
represents
a) Uvea
b) Cornea and conjunctiva
c) Fibrous coat
d) Iris
20. Myopia can be corrected by
a) Cylindrical lens
b) Bifocal lens
c) Biconvex lens
d) Biconcave lens
21. The other name of internal ear is
a) Utriculus
b) Membranous labyrinth
c) Sacculus
d) Ductus endolymphaticus
22. Color to the eye is imparted by
a) Lens b) Pupil
c) Iris d) Vitreous humour
23. Receptors for initial contact and movement
of object over the skin are
a) Pacinian corpuscles
b) Hair end organs
c) Merkel’s discs
d) Ruffini’s corpuscles
24. The order of the three layers of cells in the
retina of human eye from inside to outside
is
a) Bipolar cells, photoreceptor cells,
ganglion cells
b) Ganglion cells, rods, cones
c) Ganglion cells, bipolar cells,
photoreceptor cells
d) Photoreceptor cells, ganglion cells,
bipolar cells
25. In the central region of the retina, there is a
yellowish spot, the macula lutea, with a
depression in its centre that produces the
sharpest vision. This depression is called
a) Optic disc b) Rods and cones
c) Vitreous body d) Fovea centralis
90
26. The knee jerk reflex in response to a mallet
tap over the patellar ligament
a) Is a conditioned reflex
b) Is a monosynaptic reflex
c) Has its reflex centre in the spinal cord
d) Is mediated by a three neuron reflex arc
27. In myopia or short sightedness
a) Image is formed slightly in front of retina
because eye ball is longer
b) Eyeball is normal but images are formed
over blind spot
c) Eyeball is normal but images are formed
slightly behind the retina due to faulty
lens
d) Curvature of cornea becomes irregular
28. Fenestra ovalis is the opening of
a) Cranium
b) Tympanum
c) Tympanic cavity
d) Brain
29. Which pigment helps some nocturnal
animal to see at night
a) Haemoglobin b) Porphyrin
c) Guanine d) Heparin
30. Organ of corti in rabbit is concerned with
the sense of
a) Smell b) Hearing
c) Taste d) Equilibrium
31. Chamber containing vitreous humour is
present
a) In front of lens
b) Behind the lens
c) Between lens and iris
d) Between iris and cornea
32. Rods and cones are present in
a) Iris b) Cornea
c) Sclerotic d) Retina
33. In glaucoma
a) Eye ball elongates
b) Eye ball shortened
c) Fluid pressure increase in eye
d) Cornea becomes opaque
34. Color blindness in human being is due to
a) Vitamin A deficiency
b) Sex linked inheritance
c) Over activity of adrenal gland
d) Excessive drinking of alcohol
35. If the source of bright light is in front of eye
suddenly become bright
a) Pupil contract
b) Focus of lens changes
c) Vitreous humour becomes liquid like
d) Retina blood supply is cut off
36. The ear ossicles of rabbit lie in the
a) Auditory capsules
b) External auditory meatus
c) Tympanic cavity
d) Tympanic bulla
37. Iodopsin is related with
a) Brain b) Spinal cord
c) Cones d) Kidney
38. Eustachian tube connects
a) Left atrium with right atrium
b) Left ventricles with right ventricle
c) Middle ear with external ear
d) Middle ear with pharynx
26. The knee jerk reflex in response to a mallet
tap over the patellar ligament
a) Is a conditioned reflex
b) Is a monosynaptic reflex
c) Has its reflex centre in the spinal cord
d) Is mediated by a three neuron reflex arc
27. In myopia or short sightedness
a) Image is formed slightly in front of retina
because eye ball is longer
b) Eyeball is normal but images are formed
over blind spot
c) Eyeball is normal but images are formed
slightly behind the retina due to faulty
lens
d) Curvature of cornea becomes irregular
28. Fenestra ovalis is the opening of
a) Cranium
b) Tympanum
c) Tympanic cavity
d) Brain
29. Which pigment helps some nocturnal
animal to see at night
a) Haemoglobin b) Porphyrin
c) Guanine d) Heparin
30. Organ of corti in rabbit is concerned with
the sense of
a) Smell b) Hearing
c) Taste d) Equilibrium
31. Chamber containing vitreous humour is
present
a) In front of lens
b) Behind the lens
c) Between lens and iris
d) Between iris and cornea
32. Rods and cones are present in
a) Iris b) Cornea
c) Sclerotic d) Retina
33. In glaucoma
a) Eye ball elongates
b) Eye ball shortened
c) Fluid pressure increase in eye
d) Cornea becomes opaque
34. Color blindness in human being is due to
a) Vitamin A deficiency
b) Sex linked inheritance
c) Over activity of adrenal gland
d) Excessive drinking of alcohol
35. If the source of bright light is in front of eye
suddenly become bright
a) Pupil contract
b) Focus of lens changes
c) Vitreous humour becomes liquid like
d) Retina blood supply is cut off
36. The ear ossicles of rabbit lie in the
a) Auditory capsules
b) External auditory meatus
c) Tympanic cavity
d) Tympanic bulla
37. Iodopsin is related with
a) Brain b) Spinal cord
c) Cones d) Kidney
38. Eustachian tube connects
a) Left atrium with right atrium
b) Left ventricles with right ventricle
c) Middle ear with external ear
d) Middle ear with pharynx
91
Difficult Questions
1. Which of the following pair is mismatched?
a) Cerebrum – voluntary activities
b) Cerebellum – body balance
c) M.O – pneumotaxic centre
d) Spinal cord – reflex action
2. Jacobson’s organs are connected with
a) Touch b) Smell
c) Sight d) Hearing
3. Salivation in man is under the control of
a) Medulla oblongata
b) Mesencephalon
c) Hypothalamus
d) Cerebellum
4. The lacrimal gland is innervated by the
a) Facial cranial nerve
b) Optic cranial nerve
c) Ophthalmic nerve
d) Occlumotor cranial nerve
5. An inability to walk a straight line may
indicate damage to which, cranial nerve?
a) Vestibulocochlear nerve
b) Trochlear nerve
c) Facial nerve
d) Hypoglossal nerve
6. The rectus eye muscle capable of causing
the eye ball to turn laterally in a horizontal
plane is innervated by which cranial nerve?
a) Optic nerve
b) Abducens nerve
c) Facial nerve
d) Occulomotor nerve
7. Touch on the right side stimulates neurons
on
a) Right somatic sensory area
b) Right somatic motor area
c) Left somatic sensory area
d) Both (b) and (c)
8. Owls moves freely during night since they
have
a) Adjustable pupil
b) Only cones in retina
c) Only rods in retina
d) Vitamin A deficiency
9. Vitreous humour is
a) Colloid
b) Watery fluid
c) Mucoid connective tissue
d) All of the above
10. Which of the following medicine is used to
dilate pupil is
a) Atropine b) Cocaine
c) Beladona d) All of the above
11. Pecten a comb like structure is found in the
eye of
a) Amphibians b) Reptiles
c) Birds d) Mammals
12. Otoconia is
a) Nerve fibers b) Ear stones
c) Sensory hair d) None of these
13. Pacinian corpuscles are
a) Glands
b) Pain receptors
c) Naked tactile receptors
d) Encapsulated pressure receptors
14. Which portion of the cochlea responds to
low frequency sound waves?
a) The portion closest to the vestibular
window
b) The middle portion
c) The portion closest to the cochlear nerve
d) The end portion
Difficult Questions
1. Which of the following pair is mismatched?
a) Cerebrum – voluntary activities
b) Cerebellum – body balance
c) M.O – pneumotaxic centre
d) Spinal cord – reflex action
2. Jacobson’s organs are connected with
a) Touch b) Smell
c) Sight d) Hearing
3. Salivation in man is under the control of
a) Medulla oblongata
b) Mesencephalon
c) Hypothalamus
d) Cerebellum
4. The lacrimal gland is innervated by the
a) Facial cranial nerve
b) Optic cranial nerve
c) Ophthalmic nerve
d) Occlumotor cranial nerve
5. An inability to walk a straight line may
indicate damage to which, cranial nerve?
a) Vestibulocochlear nerve
b) Trochlear nerve
c) Facial nerve
d) Hypoglossal nerve
6. The rectus eye muscle capable of causing
the eye ball to turn laterally in a horizontal
plane is innervated by which cranial nerve?
a) Optic nerve
b) Abducens nerve
c) Facial nerve
d) Occulomotor nerve
7. Touch on the right side stimulates neurons
on
a) Right somatic sensory area
b) Right somatic motor area
c) Left somatic sensory area
d) Both (b) and (c)
8. Owls moves freely during night since they
have
a) Adjustable pupil
b) Only cones in retina
c) Only rods in retina
d) Vitamin A deficiency
9. Vitreous humour is
a) Colloid
b) Watery fluid
c) Mucoid connective tissue
d) All of the above
10. Which of the following medicine is used to
dilate pupil is
a) Atropine b) Cocaine
c) Beladona d) All of the above
11. Pecten a comb like structure is found in the
eye of
a) Amphibians b) Reptiles
c) Birds d) Mammals
12. Otoconia is
a) Nerve fibers b) Ear stones
c) Sensory hair d) None of these
13. Pacinian corpuscles are
a) Glands
b) Pain receptors
c) Naked tactile receptors
d) Encapsulated pressure receptors
14. Which portion of the cochlea responds to
low frequency sound waves?
a) The portion closest to the vestibular
window
b) The middle portion
c) The portion closest to the cochlear nerve
d) The end portion
92
15. In man nictitating membrane is
a) Absent b) Vestigial
c) Non-functional d) Functional
16. The middle ear and internal ear of mammals
are enclosed in which of the following bones
a) Mastoid
b) Ethmoid
c) Tympanic bulla
d) Tympanic bulla and periotic bone
(temporal bone)
17. No image formation occurs on blind spot of
retina because
a) It is not present on the optical axis of the
eye
b) Here cones and rods are absent
c) On this part only cones are present
d) The nerve fibers of this region do not
contribute in the formation of optic
chiasma
18. Hearing is controlled by
a) Cerebral hemisphere
b) Temporal lobes
c) Cerebellum
d) Hypothalamus
19. “Telescopic vision” found in
a) Amphibians b) Mammals
c) Birds d) None of these
20. How many oblique and rectus muscles are
found to move the eye ball in various
directions inside the eye orbit
a) Two b) Four
c) Sixd) Eight
21. In the tympanic cavity there is an aperture
in which the stapes is fitted it is
a) Foramen rotundus
b) Foramen triosseum
c) Fenestra ovalis
d) Fenestra rotundas
22. Eye is most sensitive to
a) 20Å b) 1000Å
c) 5000Å d) 7000Å
23. The white matter of the central nervous
system is always
a) Deep to the grey matter
b) Unmyelinated
c) Arranged into tracts
d) Composed of sensory fibers only
24. Trachoma disease is due to infection of
bacteria
a) Chlamydia trachomastis
b) Bassilus
c) E.Coli
d) Salmonella
25. Central pit of retina where visual acuity is
greatest
a) Macula lutea b) Fovea
c) Blind spot d) Lens
26. Movement of tongue muscle is controlled
by
a) Facial nerve
b) Trigeminal nerve
c) Hypoglossal nerve
d) Vagus nerve
27. Otolith (otoconia) are CaCO
3
particles found
in
a) Perilymph b) Endolymph
c) Bones d) Vitreous humour
28. Which cranial nerve is purely sensory?
a) Abducens b) Auditory
c) Vagus d) Spinal accessory
29. Movement of the eye outward away from
the nose is the function of which muscle?
a) Superior rectus b) Lateral rectus
c) Inferior oblique d) Superior oblique
15. In man nictitating membrane is
a) Absent b) Vestigial
c) Non-functional d) Functional
16. The middle ear and internal ear of mammals
are enclosed in which of the following bones
a) Mastoid
b) Ethmoid
c) Tympanic bulla
d) Tympanic bulla and periotic bone
(temporal bone)
17. No image formation occurs on blind spot of
retina because
a) It is not present on the optical axis of the
eye
b) Here cones and rods are absent
c) On this part only cones are present
d) The nerve fibers of this region do not
contribute in the formation of optic
chiasma
18. Hearing is controlled by
a) Cerebral hemisphere
b) Temporal lobes
c) Cerebellum
d) Hypothalamus
19. “Telescopic vision” found in
a) Amphibians b) Mammals
c) Birds d) None of these
20. How many oblique and rectus muscles are
found to move the eye ball in various
directions inside the eye orbit
a) Two b) Four
c) Sixd) Eight
21. In the tympanic cavity there is an aperture
in which the stapes is fitted it is
a) Foramen rotundus
b) Foramen triosseum
c) Fenestra ovalis
d) Fenestra rotundas
22. Eye is most sensitive to
a) 20Å b) 1000Å
c) 5000Å d) 7000Å
23. The white matter of the central nervous
system is always
a) Deep to the grey matter
b) Unmyelinated
c) Arranged into tracts
d) Composed of sensory fibers only
24. Trachoma disease is due to infection of
bacteria
a) Chlamydia trachomastis
b) Bassilus
c) E.Coli
d) Salmonella
25. Central pit of retina where visual acuity is
greatest
a) Macula lutea b) Fovea
c) Blind spot d) Lens
26. Movement of tongue muscle is controlled
by
a) Facial nerve
b) Trigeminal nerve
c) Hypoglossal nerve
d) Vagus nerve
27. Otolith (otoconia) are CaCO
3
particles found
in
a) Perilymph b) Endolymph
c) Bones d) Vitreous humour
28. Which cranial nerve is purely sensory?
a) Abducens b) Auditory
c) Vagus d) Spinal accessory
29. Movement of the eye outward away from
the nose is the function of which muscle?
a) Superior rectus b) Lateral rectus
c) Inferior oblique d) Superior oblique
93
30. Which of the following terms does not apply
to how light rays are processed in the eyes?
a) Refraction b) Accommodation
c) Inversion d) Dispersion
31. Ear ossicles, incus is modified form of which
bone?
a) Jugal b) Articular
c) Quadrate d) Hyomandibular
32. The musculus tensor choroidea is
a) Another name of tela choroidea
b) Muscles surrounding the lens
c) Levator bulbi muscles
d) None of the above
33. The retina of nocturnal birds contains
a) Cones only b) Rods only
c) Both (a) and (b) d) Either (a) or (b)
ANSWER KEYS
Simple Questions
1.d 2.b 3.d 4.c 5.b 6.b 7.c 8.b 9.a 10.c 11.b 12.c
13.b 14.d 15.d 16.b 17.b 18.b 19.b 20.d 21.b 22.c 23.b 24.c
25.d 26.c 27.c 28.c 29.c 30.b 31.b 32.d 33.c 34.b 35.a 36.c
37.c 38.d
Difficult Questions
1.c 2.b 3.a 4.c 5.a 6.b 7.c 8.c 9.d 10.d 11.c 12.b
13.d 14.c 15.b 16.d 17.b 18.b 19.c 20.c 21.c 22.c 23.d 24.a
25.b 26.c 27.b 28.b 29.b 30.d 31.c 32.b 33.b
30. Which of the following terms does not apply
to how light rays are processed in the eyes?
a) Refraction b) Accommodation
c) Inversion d) Dispersion
31. Ear ossicles, incus is modified form of which
bone?
a) Jugal b) Articular
c) Quadrate d) Hyomandibular
32. The musculus tensor choroidea is
a) Another name of tela choroidea
b) Muscles surrounding the lens
c) Levator bulbi muscles
d) None of the above
33. The retina of nocturnal birds contains
a) Cones only b) Rods only
c) Both (a) and (b) d) Either (a) or (b)
ANSWER KEYS
Simple Questions
1.d 2.b 3.d 4.c 5.b 6.b 7.c 8.b 9.a 10.c 11.b 12.c
13.b 14.d 15.d 16.b 17.b 18.b 19.b 20.d 21.b 22.c 23.b 24.c
25.d 26.c 27.c 28.c 29.c 30.b 31.b 32.d 33.c 34.b 35.a 36.c
37.c 38.d
Difficult Questions
1.c 2.b 3.a 4.c 5.a 6.b 7.c 8.c 9.d 10.d 11.c 12.b
13.d 14.c 15.b 16.d 17.b 18.b 19.c 20.c 21.c 22.c 23.d 24.a
25.b 26.c 27.b 28.b 29.b 30.d 31.c 32.b 33.b
94
1. Which is the proper sequence of visual
sensory transmission from stimulation of
photoreceptors located on the medial side
of the retina?
a) Optic nerve, lateral geniculate body, optic
radiation, optic tract, cerebral cortex
b) Optic nerve, optic chiasma, lateral
geniculate body, optic tract, cerebral
cortex, optic radiation
c) Optic nerve, optic chiasma, optic tract,
lateral geniculate body, optic radiation,
cerebral cortex
d) Optic nerve, optic tract, lateral geniculate
body, optic radiation, cerebral cortex
2. The structure in the internal ear which
resembles a “snail shell” is called
a) Organ of corti
b) Membranous labirynth
c) Cochlea
d) Ear ossicles
3. Our ear can hear sound waves of the
frequency
a) Above 20,000 cycles / sec
b) 5 – 100 cycles / sec
c) 50 – 20,000 cycles/sec
d) 20 – 20,000 cycles/sec
4. Cochlea of mammalian ear is concerned
with
a) Balancing of body
b) Hearing
c) Perception of atmospheric pressure
d) Both (a) and (b)
DPP - 3
5. “Organ of corti” is found in
a) Scala rotundes
b) Scala media
c) Scala vestibule
d) Scala tympani
6. Man can see objects equally clear from
various distances due to
a) Cornea b) Conjunctiva
c) Eye lid d) Ciliary muscles
7. The receptor organs for sense of hearing
are located in
a) Cochlea
b) Utriculus
c) Sacculus
d) Middle ear
8. The ciliary body is located
a) Near the ciliary muscles
b) Near the blind spot
c) Just behind the cornea
d) At the junction of iris and choroid
9. The eye defect, Astigmatism can be
corrected by using
a) Convex lens b) Concave lens
c) Cylindrical lens d) Surgery
10. Eye and ear are the example of
a) Teleoreceptor
b) Gustato receptor
c) Extero receptor
d) Intero receptor
1. Which is the proper sequence of visual
sensory transmission from stimulation of
photoreceptors located on the medial side
of the retina?
a) Optic nerve, lateral geniculate body, optic
radiation, optic tract, cerebral cortex
b) Optic nerve, optic chiasma, lateral
geniculate body, optic tract, cerebral
cortex, optic radiation
c) Optic nerve, optic chiasma, optic tract,
lateral geniculate body, optic radiation,
cerebral cortex
d) Optic nerve, optic tract, lateral geniculate
body, optic radiation, cerebral cortex
2. The structure in the internal ear which
resembles a “snail shell” is called
a) Organ of corti
b) Membranous labirynth
c) Cochlea
d) Ear ossicles
3. Our ear can hear sound waves of the
frequency
a) Above 20,000 cycles / sec
b) 5 – 100 cycles / sec
c) 50 – 20,000 cycles/sec
d) 20 – 20,000 cycles/sec
4. Cochlea of mammalian ear is concerned
with
a) Balancing of body
b) Hearing
c) Perception of atmospheric pressure
d) Both (a) and (b)
DPP - 3
5. “Organ of corti” is found in
a) Scala rotundes
b) Scala media
c) Scala vestibule
d) Scala tympani
6. Man can see objects equally clear from
various distances due to
a) Cornea b) Conjunctiva
c) Eye lid d) Ciliary muscles
7. The receptor organs for sense of hearing
are located in
a) Cochlea
b) Utriculus
c) Sacculus
d) Middle ear
8. The ciliary body is located
a) Near the ciliary muscles
b) Near the blind spot
c) Just behind the cornea
d) At the junction of iris and choroid
9. The eye defect, Astigmatism can be
corrected by using
a) Convex lens b) Concave lens
c) Cylindrical lens d) Surgery
10. Eye and ear are the example of
a) Teleoreceptor
b) Gustato receptor
c) Extero receptor
d) Intero receptor
95
4.1 INTRODUCTION TO THE ENDOCRINE SYSTEM
Communication between neighbouring cells, and between cells and tissues in distant parts of the
body, is done through either the nervous system or the endocrine system. The nervous system
utilizes electrochemical impulses to regulate muscles and glands. These signals, carried by neurons,
elicit responses in target cells within milliseconds. However, the duration of those responses is very
brief unless neuronal signalling continues. The endocrine system regulates biological processes
through the release of chemicals called hormones. Hormones are released into body fluids – usually
blood, which carries these chemicals to their target cells, where they elicit a response. The responses
elicited by hormones usually take several seconds to several days to occur, and the duration of the
response can last just as long without further signalling. Unlike nearly instantaneous nerve impulses,
hormones of the endocrine system can regulate functions of the body on longer time scales to
maintain homeostasis.
The major function of the endocrine system is to participate in homeostatic feedback loops by
acting as a means of communication between integrators and effectors, and sometimes acting as
the sensor as well. The endocrine system is also involved with growth, development and adaptation.
Within all of these changing processes, our bodies tolerate fluctuations within certain limits but still
overall homeostasis needs to be maintained.
Common dysfunctions of the endocrine system
We feel the effects of changes in the endocrine system at various points in our lives. Hormone
levels fluctuate during puberty, and even after we eat a meal. Common dysfunctions of the endocrine
system include an inability to regulate glucose, called diabetes mellitus, and an inability to regulate
calcium levels in the bones, which may lead to osteoporosis. Other common disorders of the endocrine
system include over or underproduction of thyroid hormone (hyperthyroidism and hypothyroidism,
respectively), which impacts energy metabolism.
4.2 HORMONES
Hormones are the chemical messengers of the endocrine system. They elicit specific responses by
binding to receptors on or in target cells.
The amount of a hormone circulating at any one time is affected by:
The rate of hormone production.
The rate of secretion from endocrine glands.
The rate of blood flow delivering the hormone to its target cells with specific receptors.
The availability and number of hormone receptors.
The rate of biochemical degradation and elimination of the hormone.
The time it takes the body to degrade 50% of a predetermined amount of hormone is called the
hormone’s half-life. A hormone with a long half-life would persist in the blood long after the endocrine
gland had stopped releasing it.
UNIT 4 - ENDOCRINE SYSTEM I
4.1 INTRODUCTION TO THE ENDOCRINE SYSTEM
Communication between neighbouring cells, and between cells and tissues in distant parts of the
body, is done through either the nervous system or the endocrine system. The nervous system
utilizes electrochemical impulses to regulate muscles and glands. These signals, carried by neurons,
elicit responses in target cells within milliseconds. However, the duration of those responses is very
brief unless neuronal signalling continues. The endocrine system regulates biological processes
through the release of chemicals called hormones. Hormones are released into body fluids – usually
blood, which carries these chemicals to their target cells, where they elicit a response. The responses
elicited by hormones usually take several seconds to several days to occur, and the duration of the
response can last just as long without further signalling. Unlike nearly instantaneous nerve impulses,
hormones of the endocrine system can regulate functions of the body on longer time scales to
maintain homeostasis.
The major function of the endocrine system is to participate in homeostatic feedback loops by
acting as a means of communication between integrators and effectors, and sometimes acting as
the sensor as well. The endocrine system is also involved with growth, development and adaptation.
Within all of these changing processes, our bodies tolerate fluctuations within certain limits but still
overall homeostasis needs to be maintained.
Common dysfunctions of the endocrine system
We feel the effects of changes in the endocrine system at various points in our lives. Hormone
levels fluctuate during puberty, and even after we eat a meal. Common dysfunctions of the endocrine
system include an inability to regulate glucose, called diabetes mellitus, and an inability to regulate
calcium levels in the bones, which may lead to osteoporosis. Other common disorders of the endocrine
system include over or underproduction of thyroid hormone (hyperthyroidism and hypothyroidism,
respectively), which impacts energy metabolism.
4.2 HORMONES
Hormones are the chemical messengers of the endocrine system. They elicit specific responses by
binding to receptors on or in target cells.
The amount of a hormone circulating at any one time is affected by:
The rate of hormone production.
The rate of secretion from endocrine glands.
The rate of blood flow delivering the hormone to its target cells with specific receptors.
The availability and number of hormone receptors.
The rate of biochemical degradation and elimination of the hormone.
The time it takes the body to degrade 50% of a predetermined amount of hormone is called the
hormone’s half-life. A hormone with a long half-life would persist in the blood long after the endocrine
gland had stopped releasing it.
UNIT 4 - ENDOCRINE SYSTEM I
96
4.2.1 Chemical structure of hormones
There are three general classes of hormones
A. Proteins and polypeptides, including hormones secreted by the anterior and posterior pituitary
gland, the pancreas (insulin and glucagon), the parathyroid gland (parathyroid hormone), and many
others.
B. Steroids secreted by the adrenal cortex (cortisol and aldosterone), the ovaries (estrogen and
progesterone), the testes (testosterone), and the placenta (estrogen and progesterone).
C. Derivatives of the amino acid tyrosine, secreted by the thyroid (thyroxine and triiodothyronine)
and the adrenal medullae (epinephrine and norepinephrine). There are no known polysaccharides
or nucleic acid hormones.
4.2.2 Synthesis of hormones
A. Polypeptide and protein hormones are stored in secretory vesicles until needed.
Most of the hormones in the body are polypeptides and proteins. These hormones range in size
from small peptides with as few as 3 amino acids (thyrotropin-releasing hormone) to proteins with
almost 200 amino acids (growth hormone and prolactin). In general, polypeptides with 100 or more
amino acids are called proteins, and those with fewer than 100 amino acids are referred to as
peptides.
Protein and peptide hormones are synthesized on the rough end of ER of the different endocrine
cells. They are usually synthesized first as larger proteins that are not biologically active
(preprohormones) and are cleaved to form smaller prohormones in the endoplasmic reticulum.
These are then transferred to the Golgi apparatus for packaging into secretory vesicles. In this
process, enzymes in the vesicles cleave the prohormones to produce smaller, biologically active
hormones and inactive fragments. The vesicles are stored within the cytoplasm, and many are
bound to the cell membrane until their secretion is needed.
Secretion of the hormones (as well as the inactive fragments) occurs when the secretory vesicles
fuse with the cell membrane and the granular contents are extruded into the interstitial fluid or
directly into the blood stream by exocytosis.
In many cases, the stimulus for exocytosis is an increase in cytosolic calcium concentration caused
by depolarization of the plasma membrane. In other instances, stimulation of an endocrine cell
surface receptor causes increased cyclic adenosine monophosphate (cAMP) and subsequently
activation of protein kinases that initiate secretion of the hormone. The peptide hormones are water
soluble, allowing them to enter the circulatory system easily, where they are carried to their target
tissues.
B.Steroid hormones are usually synthesized from cholesterol and are not stored.
The chemical structure of steroid hormones is similar to that of cholesterol, and in most instances
they are synthesized from cholesterol itself. They are lipid soluble and consist of three cyclohexyl
rings and one cyclopentyl ring combined into a single structure.
4.2.1 Chemical structure of hormones
There are three general classes of hormones
A. Proteins and polypeptides, including hormones secreted by the anterior and posterior pituitary
gland, the pancreas (insulin and glucagon), the parathyroid gland (parathyroid hormone), and many
others.
B. Steroids secreted by the adrenal cortex (cortisol and aldosterone), the ovaries (estrogen and
progesterone), the testes (testosterone), and the placenta (estrogen and progesterone).
C. Derivatives of the amino acid tyrosine, secreted by the thyroid (thyroxine and triiodothyronine)
and the adrenal medullae (epinephrine and norepinephrine). There are no known polysaccharides
or nucleic acid hormones.
4.2.2 Synthesis of hormones
A. Polypeptide and protein hormones are stored in secretory vesicles until needed.
Most of the hormones in the body are polypeptides and proteins. These hormones range in size
from small peptides with as few as 3 amino acids (thyrotropin-releasing hormone) to proteins with
almost 200 amino acids (growth hormone and prolactin). In general, polypeptides with 100 or more
amino acids are called proteins, and those with fewer than 100 amino acids are referred to as
peptides.
Protein and peptide hormones are synthesized on the rough end of ER of the different endocrine
cells. They are usually synthesized first as larger proteins that are not biologically active
(preprohormones) and are cleaved to form smaller prohormones in the endoplasmic reticulum.
These are then transferred to the Golgi apparatus for packaging into secretory vesicles. In this
process, enzymes in the vesicles cleave the prohormones to produce smaller, biologically active
hormones and inactive fragments. The vesicles are stored within the cytoplasm, and many are
bound to the cell membrane until their secretion is needed.
Secretion of the hormones (as well as the inactive fragments) occurs when the secretory vesicles
fuse with the cell membrane and the granular contents are extruded into the interstitial fluid or
directly into the blood stream by exocytosis.
In many cases, the stimulus for exocytosis is an increase in cytosolic calcium concentration caused
by depolarization of the plasma membrane. In other instances, stimulation of an endocrine cell
surface receptor causes increased cyclic adenosine monophosphate (cAMP) and subsequently
activation of protein kinases that initiate secretion of the hormone. The peptide hormones are water
soluble, allowing them to enter the circulatory system easily, where they are carried to their target
tissues.
B.Steroid hormones are usually synthesized from cholesterol and are not stored.
The chemical structure of steroid hormones is similar to that of cholesterol, and in most instances
they are synthesized from cholesterol itself. They are lipid soluble and consist of three cyclohexyl
rings and one cyclopentyl ring combined into a single structure.
97
Although there is usually very little hormone storage in steroid-producing endocrine cells, large
stores of cholesterol esters in cytoplasm vacuoles can be rapidly mobilized for steroid synthesis
after a stimulus. Much of the cholesterol in steroid-producing cells comes from the plasma, but
there is also de novo synthesis of cholesterol in steroid-producing cells. Because the steroids are
highly lipid soluble, once they are synthesized, they simply diffuse across the cell membrane and
enter the interstitial fluid and then the blood.
C. Amine hormones are derived from tyrosine.
The two groups of hormones derived from tyrosine, the thyroid and the adrenal medullary hormones,
are formed by the actions of enzymes in the cytoplasmic compartments of the glandular cells. The
thyroid hormones are synthesized and stored in the thyroid gland and incorporated into
macromolecules of the protein thyroglobulin, which is stored in large follicles within the thyroid
gland. Hormone secretion occurs when the amines are split from thyroglobulin, and the free hormones
are then released into the blood stream. After entering the blood, most of the thyroid hormones
combine with plasma proteins, especially thyroxine-binding globulin, which slowly releases the
hormones to the target tissues.
Epinephrine and norepinephrine are formed in the adrenal medulla, which normally secretes about
four times more epinephrine than norepinephrine. Catecholamines are taken up into preformed
vesicles and stored until secreted. Similar to the protein hormones stored in secretory granules,
catecholamines are also released from adrenal medullary cells by exocytosis. Once the
catecholamines enter the circulation, they can exist in the plasma in free form or in conjugation with
other substances.
Synthesis
Packaging
Endo-
plasmic
reticulum
Storage
Secretion
StimulusExtracellular
fluid
Secretory
vesicles
Golgi
apparatus
NucleusDNA
Transcripation
mRNA
Translation
Ca
cAMP
++
Synthesis and secretion of peptide hormones. The stimulus for hormone secretion often involves
changes in intracellular calcium or changes in cyclic adenosine monophosphate (cAMP) in the cell.
Although there is usually very little hormone storage in steroid-producing endocrine cells, large
stores of cholesterol esters in cytoplasm vacuoles can be rapidly mobilized for steroid synthesis
after a stimulus. Much of the cholesterol in steroid-producing cells comes from the plasma, but
there is also de novo synthesis of cholesterol in steroid-producing cells. Because the steroids are
highly lipid soluble, once they are synthesized, they simply diffuse across the cell membrane and
enter the interstitial fluid and then the blood.
C. Amine hormones are derived from tyrosine.
The two groups of hormones derived from tyrosine, the thyroid and the adrenal medullary hormones,
are formed by the actions of enzymes in the cytoplasmic compartments of the glandular cells. The
thyroid hormones are synthesized and stored in the thyroid gland and incorporated into
macromolecules of the protein thyroglobulin, which is stored in large follicles within the thyroid
gland. Hormone secretion occurs when the amines are split from thyroglobulin, and the free hormones
are then released into the blood stream. After entering the blood, most of the thyroid hormones
combine with plasma proteins, especially thyroxine-binding globulin, which slowly releases the
hormones to the target tissues.
Epinephrine and norepinephrine are formed in the adrenal medulla, which normally secretes about
four times more epinephrine than norepinephrine. Catecholamines are taken up into preformed
vesicles and stored until secreted. Similar to the protein hormones stored in secretory granules,
catecholamines are also released from adrenal medullary cells by exocytosis. Once the
catecholamines enter the circulation, they can exist in the plasma in free form or in conjugation with
other substances.
Synthesis
Packaging
Endo-
plasmic
reticulum
Storage
Secretion
StimulusExtracellular
fluid
Secretory
vesicles
Golgi
apparatus
NucleusDNA
Transcripation
mRNA
Translation
Ca
cAMP
++
Synthesis and secretion of peptide hormones. The stimulus for hormone secretion often involves
changes in intracellular calcium or changes in cyclic adenosine monophosphate (cAMP) in the cell.
98
HO
O
Cortisol
OH
O
CH OH
2
C
O
Testosterone
OH
HO
O
Aldosterone
O
CH OH
2
C
HC
O
HO
Estradiol
OH
HO
HO
OH
H
N
CH
3
Epinephrine
HO
HO
OH
NH
2
Norepinephrine
Thyroxine (T )
4
HO
O
NH
2
I
I
O
I
I
OH
Triiodothyronine (T )
3
HO
I
O
I
I
H
O
OH
NH
2
Chemical structures of several
steroid hormones
Amino acid tyrosine derivatives
4.2.3 Control of hormone production
Hormone production can be regulated by positive and negative feedback pathways. In positive
feedback systems, the release of a hormone leads to an action that stimulates release of more of
the same hormone.
In a hormonal negative feedback loop, when a stimulus causes the release of a hormone (hormone
A), the hormone binds to the target cell receptor, causing the necessary metabolic change toward
homeostasis. In a negative loop, the effect of this metabolic change is to counter the stimulus that
caused the release of Hormone A. Once the cause of the stimulus returns to normal range, the
production of that hormone stops and plasma level of that hormone returns to the normal (pre
stimulus) level. In this way, the concentration of most hormones in blood is maintained within a
narrow range.
4.2.4 Stimuli regulating hormone production
There are three mechanisms by which endocrine glands are stimulated to synthesize and release
hormones:
A. Humoral stimuli
Humoral stimuli regulate the release of hormones in response to specific changes in extracellular
fluids, such as the concentration of a particular ion or solute in the blood or even the overall solute
levels in the blood.
Example
A rise in blood glucose level triggers the pancreatic release of insulin. Insulin causes blood glucose
levels to drop, which signals the pancreas to decrease insulin production through a negative feedback
loop. Similarly, low blood calcium stimulates the release of parathyroid hormone from the parathyroid
gland which stimulates the release of calcium from bone, decreases calcium excretion in urine and
promotes calcium absorption in the digestive system.
HO
O
Cortisol
OH
O
CH OH
2
C
O
Testosterone
OH
HO
O
Aldosterone
O
CH OH
2
C
HC
O
HO
Estradiol
OH
HO
HO
OH
H
N
CH
3
Epinephrine
HO
HO
OH
NH
2
Norepinephrine
Thyroxine (T )
4
HO
O
NH
2
I
I
O
I
I
OH
Triiodothyronine (T )
3
HO
I
O
I
I
H
O
OH
NH
2
Chemical structures of several
steroid hormones
Amino acid tyrosine derivatives
4.2.3 Control of hormone production
Hormone production can be regulated by positive and negative feedback pathways. In positive
feedback systems, the release of a hormone leads to an action that stimulates release of more of
the same hormone.
In a hormonal negative feedback loop, when a stimulus causes the release of a hormone (hormone
A), the hormone binds to the target cell receptor, causing the necessary metabolic change toward
homeostasis. In a negative loop, the effect of this metabolic change is to counter the stimulus that
caused the release of Hormone A. Once the cause of the stimulus returns to normal range, the
production of that hormone stops and plasma level of that hormone returns to the normal (pre
stimulus) level. In this way, the concentration of most hormones in blood is maintained within a
narrow range.
4.2.4 Stimuli regulating hormone production
There are three mechanisms by which endocrine glands are stimulated to synthesize and release
hormones:
A. Humoral stimuli
Humoral stimuli regulate the release of hormones in response to specific changes in extracellular
fluids, such as the concentration of a particular ion or solute in the blood or even the overall solute
levels in the blood.
Example
A rise in blood glucose level triggers the pancreatic release of insulin. Insulin causes blood glucose
levels to drop, which signals the pancreas to decrease insulin production through a negative feedback
loop. Similarly, low blood calcium stimulates the release of parathyroid hormone from the parathyroid
gland which stimulates the release of calcium from bone, decreases calcium excretion in urine and
promotes calcium absorption in the digestive system.
99
B. Tropic hormonal stimuli
With tropic hormonal stimuli, a hormone is produced and released by an endocrine gland in
response to another hormone (known as “tropic hormone”). These hormones controlling release of
another hormone are called tropic (meaning “turn toward”).
Example
The hypothalamus produces hormones that stimulate the anterior pituitary. The anterior pituitary in
turn releases hormones that regulate hormone production by other endocrine glands. For example,
the anterior pituitary releases thyroid stimulating hormone, which stimulates the thyroid gland to
produce the hormones T
3
and T
4
. As blood concentrations of T
3
and T
4
rise, they inhibit further
hormone production by both the pituitary and the hypothalamus in a negative feedback loop.
C. Neural stimuli
The nervous system can also directly stimulate endocrine glands to release hormones through a
mechanism known as neural stimuli.
Example
Neuronal signalling from the sympathetic nervous system directly stimulates the adrenal medulla to
release the hormones epinephrine and norepinephrine in response to stress.
4.2.5 Transport in blood
Water-soluble hormones (peptides and catecholamines) are dissolved in the plasma and
transported from their sites of synthesis to target tissues, where they diffuse out of the capillaries,
into the interstitial fluid, and ultimately to target cells.
Steroid and thyroid hormones, in contrast, circulate in the blood mainly bound to plasma proteins.
Usually less than 10% of steroid or thyroid hormones in the plasma exist free in solution. For example,
more than 99% of the thyroxine in the blood is bound to plasma proteins. However, protein-bound
hormones cannot easily diffuse across the capillaries and gain access to their target cells and are
therefore biologically inactive until they dissociate from plasma proteins.
The relatively large amounts of hormones bound to proteins serve as reservoirs, replenishing the
concentration of free hormones when they are bound to target receptors or lost from the circulation.
Binding of hormones to plasma proteins greatly slows their clearance from the plasma.
4.2.6 Clearance from blood
Two factors can increase or decrease the concentration of a hormone in the blood:
Rate of hormone secretion into the blood
Rate of removal of the hormone from the blood, called the metabolic clearance rate.
Rate of disappearance of hormone from plasma
Metaboli cclearance rate =
Conc. of hormone in each ml of plasma
B. Tropic hormonal stimuli
With tropic hormonal stimuli, a hormone is produced and released by an endocrine gland in
response to another hormone (known as “tropic hormone”). These hormones controlling release of
another hormone are called tropic (meaning “turn toward”).
Example
The hypothalamus produces hormones that stimulate the anterior pituitary. The anterior pituitary in
turn releases hormones that regulate hormone production by other endocrine glands. For example,
the anterior pituitary releases thyroid stimulating hormone, which stimulates the thyroid gland to
produce the hormones T
3
and T
4
. As blood concentrations of T
3
and T
4
rise, they inhibit further
hormone production by both the pituitary and the hypothalamus in a negative feedback loop.
C. Neural stimuli
The nervous system can also directly stimulate endocrine glands to release hormones through a
mechanism known as neural stimuli.
Example
Neuronal signalling from the sympathetic nervous system directly stimulates the adrenal medulla to
release the hormones epinephrine and norepinephrine in response to stress.
4.2.5 Transport in blood
Water-soluble hormones (peptides and catecholamines) are dissolved in the plasma and
transported from their sites of synthesis to target tissues, where they diffuse out of the capillaries,
into the interstitial fluid, and ultimately to target cells.
Steroid and thyroid hormones, in contrast, circulate in the blood mainly bound to plasma proteins.
Usually less than 10% of steroid or thyroid hormones in the plasma exist free in solution. For example,
more than 99% of the thyroxine in the blood is bound to plasma proteins. However, protein-bound
hormones cannot easily diffuse across the capillaries and gain access to their target cells and are
therefore biologically inactive until they dissociate from plasma proteins.
The relatively large amounts of hormones bound to proteins serve as reservoirs, replenishing the
concentration of free hormones when they are bound to target receptors or lost from the circulation.
Binding of hormones to plasma proteins greatly slows their clearance from the plasma.
4.2.6 Clearance from blood
Two factors can increase or decrease the concentration of a hormone in the blood:
Rate of hormone secretion into the blood
Rate of removal of the hormone from the blood, called the metabolic clearance rate.
Rate of disappearance of hormone from plasma
Metaboli cclearance rate =
Conc. of hormone in each ml of plasma
100
Hormones are “cleared” from the plasma in several ways, including:
1. Metabolic destruction by the tissues.
2. Binding with the tissues.
3. Excretion by the liver into the bile, and
4. Excretion by the kidneys into the urine.
For certain hormones, a decreased metabolic clearance rate may cause an excessively high
concentration of the hormone in the circulating body fluids. For instance, this occurs for several of
the steroid hormones when the liver is diseased, because these hormones are conjugated mainly in
the liver and then “cleared” into the bile.
Hormones are sometimes degraded at their target cells by enzymatic processes that cause
endocytosis of the cell membrane hormone receptor complex: the hormone is then metabolized in
the cell, and the receptors are usually recycled back to the cell membrane.
4.2.7. Hormone receptors
Hormones mediate changes in cells by binding to specific receptors; individual hormones have
their own unique receptor or class of receptors. A cell that has a receptor for a specific hormone is
called a target cell. A hormone can, therefore circulate throughout the body, contacting many different
cell types, but affecting only those cells that possess the specific receptor. A receptor is a protein
(cell membrane or intracellular) that binds specifically to a particular hormone. Receptors for a
specific hormone may be found in or on many different target cells, or may be limited to a small
number of specialized cells.
The number of receptors that respond to a hormone determine the cell’s potential sensitivivty to that
hormone and the resulting cellular response. The number of receptors that respond to a hormone
can change, resulting in increased or decreased cell sensitivity. Since alcohol (ethanol) inhibits
glutamate receptor channels, people with high alcohol levels show higher number of glutamate
receptors in a classic example of up – regulation that makes the cells more sensitive to the hormone
to try to maintain the normal level of response to glutamate (homeostasis). The number of cell
surface receptors can also decrease in response to rising hormone levels, called down regulation,
leading to reduced cellular response to the hormone. Thus, the action of a hormone can be regulated
either by the amount of hormone in circulation or by the number of receptors (either inside the cell or
on the cell surface) available at that time for that hormone.
Hormones bind to receptors and cause changes in cellular function. Receptors can be found either
inside the cell (intracellular receptors) or on the cell’s surface (plasma membrane receptors).
A. Intracellular receptors
Steroid hormones are lipophillic and need transport proteins in the blood. Once released from their
transport protein, the non polar hormone is able to diffuse across the plasma membrane of cells.
Recall that the lipid bilayer of the plasma membrane of cells uses amphiphillic phospholipids to
Hormones are “cleared” from the plasma in several ways, including:
1. Metabolic destruction by the tissues.
2. Binding with the tissues.
3. Excretion by the liver into the bile, and
4. Excretion by the kidneys into the urine.
For certain hormones, a decreased metabolic clearance rate may cause an excessively high
concentration of the hormone in the circulating body fluids. For instance, this occurs for several of
the steroid hormones when the liver is diseased, because these hormones are conjugated mainly in
the liver and then “cleared” into the bile.
Hormones are sometimes degraded at their target cells by enzymatic processes that cause
endocytosis of the cell membrane hormone receptor complex: the hormone is then metabolized in
the cell, and the receptors are usually recycled back to the cell membrane.
4.2.7. Hormone receptors
Hormones mediate changes in cells by binding to specific receptors; individual hormones have
their own unique receptor or class of receptors. A cell that has a receptor for a specific hormone is
called a target cell. A hormone can, therefore circulate throughout the body, contacting many different
cell types, but affecting only those cells that possess the specific receptor. A receptor is a protein
(cell membrane or intracellular) that binds specifically to a particular hormone. Receptors for a
specific hormone may be found in or on many different target cells, or may be limited to a small
number of specialized cells.
The number of receptors that respond to a hormone determine the cell’s potential sensitivivty to that
hormone and the resulting cellular response. The number of receptors that respond to a hormone
can change, resulting in increased or decreased cell sensitivity. Since alcohol (ethanol) inhibits
glutamate receptor channels, people with high alcohol levels show higher number of glutamate
receptors in a classic example of up – regulation that makes the cells more sensitive to the hormone
to try to maintain the normal level of response to glutamate (homeostasis). The number of cell
surface receptors can also decrease in response to rising hormone levels, called down regulation,
leading to reduced cellular response to the hormone. Thus, the action of a hormone can be regulated
either by the amount of hormone in circulation or by the number of receptors (either inside the cell or
on the cell surface) available at that time for that hormone.
Hormones bind to receptors and cause changes in cellular function. Receptors can be found either
inside the cell (intracellular receptors) or on the cell’s surface (plasma membrane receptors).
A. Intracellular receptors
Steroid hormones are lipophillic and need transport proteins in the blood. Once released from their
transport protein, the non polar hormone is able to diffuse across the plasma membrane of cells.
Recall that the lipid bilayer of the plasma membrane of cells uses amphiphillic phospholipids to
101
compartmentalize the cytoplasm of a cell. When a steroid hormone crosses the plasma membrane
of a target cell, it binds to an intracellular hormone receptor in the cytoplasm, on intracellular
membrane system (ER) or, within the nucleus of the cell. The receptor/ hormone complex can then
bind to a specific site on DNA and act as a transcription regulator to increase or decrease the
synthesis of particular mRNA molecules coded by these specific genes. This, in turn, alters mRNA
production, which determines the amount of corresponding protein that is synthesized. The steroid
hormone regulates specific cell processes. The rate of transcriptiion and protein synthesis is directly
proportional to the amount of hormone forming receptor/ hormone complexes; so if the hormone
production increases, so does the physiological effect in the body.
The thyroid hormones, T
3
and T
4
, also use plasma transport proteins and intracellular DNA binding
receptors. There are, however, some important physiological differences with the steroid hormone
mechanism. The target cells have membrane transport proteins that transport the thyroid hormones
into the cell. The thyroid hormone receptors is found bound to a transcription repressor protein on
the DNA. The binding of the hormone with the receptor repressor complex to form the receptor/
hormone complex causes the repressor protein to dissociate, and a transcription activator protein
becomes associated with the receptor. This, in turn, initiates transcription.
Lipophilic hormone
Diffusion
Extracellular fluid
Target cell
Proteins
Proteins
mRNA
Nuclear envelope
Nuclear pore
Mechanisms of interaction of lipophilic hormones, such as
steroids, with intracellular receptors in target cells.
Cytoplasmic
receptor Hormone
receptor
complex
Nuclear
receptor
DNA
Nucleus
mRNA
Hormone
receptor
element
B. Plasma membrane hormone receptors
Most peptide and amino acid hormones are polar and therefore cannot diffuse through the plasma
membrane of cells. So, they bond to plasma membrane hormone receptors on the outer surface
of the plasma membrane. Unlike steroid hormones, polar hormones also alter intracellular processes
compartmentalize the cytoplasm of a cell. When a steroid hormone crosses the plasma membrane
of a target cell, it binds to an intracellular hormone receptor in the cytoplasm, on intracellular
membrane system (ER) or, within the nucleus of the cell. The receptor/ hormone complex can then
bind to a specific site on DNA and act as a transcription regulator to increase or decrease the
synthesis of particular mRNA molecules coded by these specific genes. This, in turn, alters mRNA
production, which determines the amount of corresponding protein that is synthesized. The steroid
hormone regulates specific cell processes. The rate of transcriptiion and protein synthesis is directly
proportional to the amount of hormone forming receptor/ hormone complexes; so if the hormone
production increases, so does the physiological effect in the body.
The thyroid hormones, T
3
and T
4
, also use plasma transport proteins and intracellular DNA binding
receptors. There are, however, some important physiological differences with the steroid hormone
mechanism. The target cells have membrane transport proteins that transport the thyroid hormones
into the cell. The thyroid hormone receptors is found bound to a transcription repressor protein on
the DNA. The binding of the hormone with the receptor repressor complex to form the receptor/
hormone complex causes the repressor protein to dissociate, and a transcription activator protein
becomes associated with the receptor. This, in turn, initiates transcription.
Lipophilic hormone
Diffusion
Extracellular fluid
Target cell
Proteins
Proteins
mRNA
Nuclear envelope
Nuclear pore
Mechanisms of interaction of lipophilic hormones, such as
steroids, with intracellular receptors in target cells.
Cytoplasmic
receptor Hormone
receptor
complex
Nuclear
receptor
DNA
Nucleus
mRNA
Hormone
receptor
element
B. Plasma membrane hormone receptors
Most peptide and amino acid hormones are polar and therefore cannot diffuse through the plasma
membrane of cells. So, they bond to plasma membrane hormone receptors on the outer surface
of the plasma membrane. Unlike steroid hormones, polar hormones also alter intracellular processes
and can also affect the target cell’s transcription. Since they cannot enter the cell and act directly on
any DNA binding proteins, they exert their transcriptional effects through intermediate molecules
called second messengers as described below. Catecholamines (amine class) and polar eicosanoids
(lipid derived class) also bind to cell surface hormone receptors.
Binding of these hormones to a cell membrane surface receptors results in activation of a signalling
pathway that triggers a cascade of intracellular activity and specific effects associated with the
hormone. Most hormones that bind at the surface receptor remain outside the target cell. Some
hormones are taken into the cell by endocytosis to initiate the intracellular biochemical response
form within vesicles. The hormone that initiates the signalling pathway, the first messenger, activates
a second messenger within the cell.
(i) G protein coupled receptors
G proteins are a class of trans membrane cell surface proteins that can be activated by hormones
or ions and other chemicals for cell signalling. G- Proteins remain inactive unless a hormone is
bound to its cell surface receptor. Inactive G proteins are bound to GDP on its cytoplasmic side.
When a hormone binds to the cell surface receptor the bound GDP is replaced by GTP.
Receptor
Hormone
Extracellular
fluid
Cytoplasm
GTP activated
target protein
(enzyme)
GTP
G-protein (active)
G-protein
(inactive)
GTP
Mechanism of activation of a G-protein–coupled receptor
Activated G proteins can have different functions depending on the hormone receptor: it can open
a membrane protein channel; it can release a small molecule; or it can activate a membrane
bound enzyme. There is a large variety of G proteins induced effects. For example, G protein
linked ion channels can stimulate movements of ions across the membranes. There are specific
channels for potassium, sodium, calcium or chloride.
For G protein activated membrane bound enzymes, there are large numbers of activated
enzymes. One of the membrane bound enzymes that the G proteins coupled receptor (GPCR)
activates upon binding to a hormone molecule is the adenylate cyclase. This enzyme catalyses
the conversion of ATP to cyclic AMP (cAMP). This, in turn, activates a class of enzymes called
protein kinases. These kinases transfer a phosphate group from ATP to a substrate molecule
in a process called phosphorylation. The phosphorylation of a substrate molecule changes its
shape, thereby activating
any DNA binding proteins, they exert their transcriptional effects through intermediate molecules
called second messengers as described below. Catecholamines (amine class) and polar eicosanoids
(lipid derived class) also bind to cell surface hormone receptors.
Binding of these hormones to a cell membrane surface receptors results in activation of a signalling
pathway that triggers a cascade of intracellular activity and specific effects associated with the
hormone. Most hormones that bind at the surface receptor remain outside the target cell. Some
hormones are taken into the cell by endocytosis to initiate the intracellular biochemical response
form within vesicles. The hormone that initiates the signalling pathway, the first messenger, activates
a second messenger within the cell.
(i) G protein coupled receptors
G proteins are a class of trans membrane cell surface proteins that can be activated by hormones
or ions and other chemicals for cell signalling. G- Proteins remain inactive unless a hormone is
bound to its cell surface receptor. Inactive G proteins are bound to GDP on its cytoplasmic side.
When a hormone binds to the cell surface receptor the bound GDP is replaced by GTP.
Receptor
Hormone
Extracellular
fluid
Cytoplasm
GTP activated
target protein
(enzyme)
GTP
G-protein (active)
G-protein
(inactive)
GTP
Mechanism of activation of a G-protein–coupled receptor
Activated G proteins can have different functions depending on the hormone receptor: it can open
a membrane protein channel; it can release a small molecule; or it can activate a membrane
bound enzyme. There is a large variety of G proteins induced effects. For example, G protein
linked ion channels can stimulate movements of ions across the membranes. There are specific
channels for potassium, sodium, calcium or chloride.
For G protein activated membrane bound enzymes, there are large numbers of activated
enzymes. One of the membrane bound enzymes that the G proteins coupled receptor (GPCR)
activates upon binding to a hormone molecule is the adenylate cyclase. This enzyme catalyses
the conversion of ATP to cyclic AMP (cAMP). This, in turn, activates a class of enzymes called
protein kinases. These kinases transfer a phosphate group from ATP to a substrate molecule
in a process called phosphorylation. The phosphorylation of a substrate molecule changes its
shape, thereby activating
103
it. This chain of reactions, where hormone binding to the GPCR leads to the appearance of cAMP in
the cytoplasm as the second messenger which, in turn, leads to the activation of protein kinase is an
example of a “reaction cascade”. In this case, since a signal from the exterior of the cell is transferred
to the interior via the formation of a “second messenger” the process is called “signal transduction
cascade”. Other second messengers that can be involved as a result of hormone binding to a cell
membrane receptor include cyclic GMP (derived from guanosisne triphosphate), tyrosine kinase,
inositol phospholipids, and even calcium ions. Cellular responses to hormone binding of a cell
membrane receptor include altering membrane permeability, activating metabolic pathways,
stimulating synthesis of proteins and enzymes, and hormone release.
The binding of a hormone at a single cell membrane receptor causes the activation of many G
proteins which can catalyse many reactions simultaneously. Thus, the effet of a peptide hormone is
amplified as the signalling cascade progresses. A small amount of hormone can trigger the formation
of a large amount of cellular product. To stop hormone activity, the cascading chemical reaction is
interrupted; for example cAMP is deactivated by the cytoplasmic enzyme phosphodiesterase (PDE).
PDE is always present in the cell, and it breakdown cAMP spontaneously, preventing overproduction
of cellular products. The specific response of a cell to a lipid insoluble hormone depends on the type
of receptors that are present on the cell membrane and the substrate molecules present in the cell
cytoplasm.
Extracellular
fluid Hormone
Cytoplasm
Adenylyl
cyclase
ATPcAMP
Inactive
cAMP-
dependent
protein kinase
Active cAMP-
dependent
protein kinase
Protein
– Po4 + ADP Protein + ATP
Cell`s response
Cyclic adenosine monophosphate (cAMP) mechanism
GTP
it. This chain of reactions, where hormone binding to the GPCR leads to the appearance of cAMP in
the cytoplasm as the second messenger which, in turn, leads to the activation of protein kinase is an
example of a “reaction cascade”. In this case, since a signal from the exterior of the cell is transferred
to the interior via the formation of a “second messenger” the process is called “signal transduction
cascade”. Other second messengers that can be involved as a result of hormone binding to a cell
membrane receptor include cyclic GMP (derived from guanosisne triphosphate), tyrosine kinase,
inositol phospholipids, and even calcium ions. Cellular responses to hormone binding of a cell
membrane receptor include altering membrane permeability, activating metabolic pathways,
stimulating synthesis of proteins and enzymes, and hormone release.
The binding of a hormone at a single cell membrane receptor causes the activation of many G
proteins which can catalyse many reactions simultaneously. Thus, the effet of a peptide hormone is
amplified as the signalling cascade progresses. A small amount of hormone can trigger the formation
of a large amount of cellular product. To stop hormone activity, the cascading chemical reaction is
interrupted; for example cAMP is deactivated by the cytoplasmic enzyme phosphodiesterase (PDE).
PDE is always present in the cell, and it breakdown cAMP spontaneously, preventing overproduction
of cellular products. The specific response of a cell to a lipid insoluble hormone depends on the type
of receptors that are present on the cell membrane and the substrate molecules present in the cell
cytoplasm.
Extracellular
fluid Hormone
Cytoplasm
Adenylyl
cyclase
ATPcAMP
Inactive
cAMP-
dependent
protein kinase
Active cAMP-
dependent
protein kinase
Protein
– Po4 + ADP Protein + ATP
Cell`s response
Cyclic adenosine monophosphate (cAMP) mechanism
GTP
104
(ii) Protein Tyrosine Kinases (PTKs) mechanism
PTKs catalyze the transfer of -phosphate of ATP to tyrosine residues on protein substrates.
Phosphorylation of tyrosine residues modulates enzymatic activity and creates binding sites for the
recruitment of downstream signaling proteins. Two classes of PTKs are present in cells: the
transmembrane receptor PTKs and the non-receptor PTKs. Because PTKs are critical components
of cellular signaling pathways, their catalytic activity is strictly regulated.
For transport of insulin, insulin receptor is found in cell membrane made up of 4 subunits. 2 subunits
(-proteins) situated towards the outside of cell membrane, bind the insulin hormone. 2 subunits (-
proteins) protrude into the cytoplasm of the cell and has tyrosine kinase activity. These receptors
are usually <100 in most of our body cells but may be >1,00,000 as in some liver cells. Binding of
insulin to the outer -subunits of receptor triggers tyrosine kinase activity of the intracellular portion
of -subunits. This causes structural changes in -subunit to become an activated tyrosine kinase.
The activated tyrosine kinase produces autophosphorylation of the cytoplasmic receptor as well as
phosphorylation of some cytoplasmic protein.
Insulin receptor
ExtracellularSubunit:
insulin
binding site
I. C. F
Cytoplasmic
Insulin
Subunit:
Tyrosine kinase
domain
P
PP
PP
PP
P
Insulin receptor substrate
(iii)Phospholipid second messenger system
Some hormones activate transmembrane receptors that activate the enzyme phospholipase C
attached to the inside projections of the receptors. This enzyme catalyzes the breakdown of some
phospholipids in the cell membrane, especially phosphatidylinositol biphosphate (PIP2), into two
different second messenger products: inositol triphosphate (IP3) and diacylglycerol (DAG). The IP3
mobilizes calcium ions from mitochondria and the endoplasmic reticulum, and the calcium ions
then have their own second messenger effects. Ca
2+
, acting as a second messenger, activate
calmodulin which induces a change in the shape and function of a particular intracellular protein.
Many of the Ca
++
dependent cellular events are triggered by activation of calmodulin. The altered
protein then produces the desired cellular response dictated by the extracellular messenger.
(ii) Protein Tyrosine Kinases (PTKs) mechanism
PTKs catalyze the transfer of -phosphate of ATP to tyrosine residues on protein substrates.
Phosphorylation of tyrosine residues modulates enzymatic activity and creates binding sites for the
recruitment of downstream signaling proteins. Two classes of PTKs are present in cells: the
transmembrane receptor PTKs and the non-receptor PTKs. Because PTKs are critical components
of cellular signaling pathways, their catalytic activity is strictly regulated.
For transport of insulin, insulin receptor is found in cell membrane made up of 4 subunits. 2 subunits
(-proteins) situated towards the outside of cell membrane, bind the insulin hormone. 2 subunits (-
proteins) protrude into the cytoplasm of the cell and has tyrosine kinase activity. These receptors
are usually <100 in most of our body cells but may be >1,00,000 as in some liver cells. Binding of
insulin to the outer -subunits of receptor triggers tyrosine kinase activity of the intracellular portion
of -subunits. This causes structural changes in -subunit to become an activated tyrosine kinase.
The activated tyrosine kinase produces autophosphorylation of the cytoplasmic receptor as well as
phosphorylation of some cytoplasmic protein.
Insulin receptor
ExtracellularSubunit:
insulin
binding site
I. C. F
Cytoplasmic
Insulin
Subunit:
Tyrosine kinase
domain
P
PP
PP
PP
P
Insulin receptor substrate
(iii)Phospholipid second messenger system
Some hormones activate transmembrane receptors that activate the enzyme phospholipase C
attached to the inside projections of the receptors. This enzyme catalyzes the breakdown of some
phospholipids in the cell membrane, especially phosphatidylinositol biphosphate (PIP2), into two
different second messenger products: inositol triphosphate (IP3) and diacylglycerol (DAG). The IP3
mobilizes calcium ions from mitochondria and the endoplasmic reticulum, and the calcium ions
then have their own second messenger effects. Ca
2+
, acting as a second messenger, activate
calmodulin which induces a change in the shape and function of a particular intracellular protein.
Many of the Ca
++
dependent cellular events are triggered by activation of calmodulin. The altered
protein then produces the desired cellular response dictated by the extracellular messenger.
105
DAG, the other lipid second messenger, activates the enzyme protein kinase C (PKC), which then
phosphorylates a large number of proteins, leading to the cell’s response.
Extracellular fluid
Receptor
Peptide
hormone
G protein
Phospholipase G
Cell membrane
DAG + IP
3
PIP
2
Cytoplasm
Active
protein
kinase C
Inactive
protein
kinase C
Protein PO
4–
Cell’s response
Cell’s response
Ca
++
Protein
Endoplasmic reticulum
The cell membrane phospholipid second messenger system
4.3 SOME BASIC COMPARISONS
Differences between nervous and endocrine coordination
Nervous coordination Endocrine coordination
(chemical coordination)
Information passes as electrical impulses Information passes as a chemical substance
along nerve fibers. through blood and lymph.
Rapid transmission of information. Slow transmission of information
Response is immediate, very exact and Response is usually slow, widespread and long
short lived. lasting.
DAG, the other lipid second messenger, activates the enzyme protein kinase C (PKC), which then
phosphorylates a large number of proteins, leading to the cell’s response.
Extracellular fluid
Receptor
Peptide
hormone
G protein
Phospholipase G
Cell membrane
DAG + IP
3
PIP
2
Cytoplasm
Active
protein
kinase C
Inactive
protein
kinase C
Protein PO
4–
Cell’s response
Cell’s response
Ca
++
Protein
Endoplasmic reticulum
The cell membrane phospholipid second messenger system
4.3 SOME BASIC COMPARISONS
Differences between nervous and endocrine coordination
Nervous coordination Endocrine coordination
(chemical coordination)
Information passes as electrical impulses Information passes as a chemical substance
along nerve fibers. through blood and lymph.
Rapid transmission of information. Slow transmission of information
Response is immediate, very exact and Response is usually slow, widespread and long
short lived. lasting.
106
Difference between hormones and enzymes
Differences between hormones and vitamins
TARGET POINTS
Endocrinology: The branch of biology dealing with the study of endocrine system and its
physiology.
Thomas Addison is known as the Father of Endocrinology.
Hormones Enzymes
Produced at one site and passed by blood May act as site where they are produced or carried
to another site for action. to another site for action
Have low molecular weight Have very high molecular weight.
Hormones may be steroids, proteins, Enzymes are proteins.
peptides or amino acid derivatives.
They are used up in their actions, effective They are not used up in their action, also act in low
in low concentration, their excess or concentration. However, the rate of enzyme
deficiency may cause disorders. catalysed reactions steadily increase with an
increase in their concentration.
May act slowly or quickly, may accelerate Act slowly, speed up the reactions.
or retard the specific reactions.
Hormone controlled reactions are not Enzyme controlled reactions are reversible.
reversible.
Hormones Vitamins
May be steroids, proteins, peptides or Are never proteins but simple organic
amino acid derivatives compounds such as amines, esters, alcohol,
aldehyde or organic acids.
Are effective in low concentration. Their They are needed in small quantity. Excess
excess or deficiency may cause hormonal vitamins are excreted. Their deficiency causes
disorders. malfunctioning called deficiency disease or
avitaminosis.
Secreted by the animal in its own body. Rarely synthesized in the body, mostly taken with
food.
Hormones influence the genes to produce They act as coenzymes and help enzymes to
specific enzymes required during perform their function.
metabolism.
They do not influence the working of those They are not produced by body organs (except
organs which have secreted them. vitamin D)
Difference between hormones and enzymes
Differences between hormones and vitamins
TARGET POINTS
Endocrinology: The branch of biology dealing with the study of endocrine system and its
physiology.
Thomas Addison is known as the Father of Endocrinology.
Hormones Enzymes
Produced at one site and passed by blood May act as site where they are produced or carried
to another site for action. to another site for action
Have low molecular weight Have very high molecular weight.
Hormones may be steroids, proteins, Enzymes are proteins.
peptides or amino acid derivatives.
They are used up in their actions, effective They are not used up in their action, also act in low
in low concentration, their excess or concentration. However, the rate of enzyme
deficiency may cause disorders. catalysed reactions steadily increase with an
increase in their concentration.
May act slowly or quickly, may accelerate Act slowly, speed up the reactions.
or retard the specific reactions.
Hormone controlled reactions are not Enzyme controlled reactions are reversible.
reversible.
Hormones Vitamins
May be steroids, proteins, peptides or Are never proteins but simple organic
amino acid derivatives compounds such as amines, esters, alcohol,
aldehyde or organic acids.
Are effective in low concentration. Their They are needed in small quantity. Excess
excess or deficiency may cause hormonal vitamins are excreted. Their deficiency causes
disorders. malfunctioning called deficiency disease or
avitaminosis.
Secreted by the animal in its own body. Rarely synthesized in the body, mostly taken with
food.
Hormones influence the genes to produce They act as coenzymes and help enzymes to
specific enzymes required during perform their function.
metabolism.
They do not influence the working of those They are not produced by body organs (except
organs which have secreted them. vitamin D)
107
Exocrine glands which secrete enzymes are glands with ducts whereas endocrine glands pour
their secretion directly into blood and lack ducts, so also called ductless glands.
The action of lipid soluble hormone is slower and lasts longer than the action of water soluble
hormone.
The following hormones exhibit the cAMP mechanism: Adrenocorticotropin (ACTH), Secretin,
Thyroid stimulating hormone (TSH), Catecholamines, Luteinizing hormone (LH), most
hypothalamic releasing hormones, Follicle stimulating hormone (FSH), Vasopressin/ADH,
Parathyroid hormone (PTH), Glucagon.
Amplification: A single molecule of adrenaline releases as many as 100 million molecules of
glucose within only 1 minute. Amplification means the magnitude of the output of a system is
much greater than the input. Second messenger cAMP can induce widely differing responses
in different cells, depending on what proteins are modified.
Chalones: The hormones which are secreted from one endocrine gland to stimulate other
endocrine gland is called as Chalones.
Autocoide: The hormone which are secreted from one endocrine gland to target organ is
called as autocoide.
Diabetogenic: The hormone which mainly affects or stimulates carbohydrate metabolism is
called as Diabetogenic.
Ketogenic: The hormone, which mainly affect the fat metabolism.
Calorgenic: The hormone, which mainly affects the basal metabolic rate (BMR) is called as
calorigenic.
Exocrine glands which secrete enzymes are glands with ducts whereas endocrine glands pour
their secretion directly into blood and lack ducts, so also called ductless glands.
The action of lipid soluble hormone is slower and lasts longer than the action of water soluble
hormone.
The following hormones exhibit the cAMP mechanism: Adrenocorticotropin (ACTH), Secretin,
Thyroid stimulating hormone (TSH), Catecholamines, Luteinizing hormone (LH), most
hypothalamic releasing hormones, Follicle stimulating hormone (FSH), Vasopressin/ADH,
Parathyroid hormone (PTH), Glucagon.
Amplification: A single molecule of adrenaline releases as many as 100 million molecules of
glucose within only 1 minute. Amplification means the magnitude of the output of a system is
much greater than the input. Second messenger cAMP can induce widely differing responses
in different cells, depending on what proteins are modified.
Chalones: The hormones which are secreted from one endocrine gland to stimulate other
endocrine gland is called as Chalones.
Autocoide: The hormone which are secreted from one endocrine gland to target organ is
called as autocoide.
Diabetogenic: The hormone which mainly affects or stimulates carbohydrate metabolism is
called as Diabetogenic.
Ketogenic: The hormone, which mainly affect the fat metabolism.
Calorgenic: The hormone, which mainly affects the basal metabolic rate (BMR) is called as
calorigenic.
108
1. A heterocrine gland is one, which
a) Has two distinct parts
b) Serves a double function of exocrine and
endocrine gland
c) Produces two types of hormones
d) Occurs in two places
2. W hich gland is both exocrine and
endocrine?
a) Pancreas b) Thyroid
c) Pituitary d) Adrenal
3. Who is known as ‘Father of endocrinology’?
a) R.H Whittaker b) Pasteur
c) Einthoven d) Thomas Addison
4. First discovered hormone
a) Thyroxine b) Adrenaline
c) Secretin d) Insulin
5. Term ‘Hormone’ was coined by
a) WM Bayliss b) EH Schally
c) EH Starling d) GW Horris
6. Which of the following is true for the effect
of steroid hormone?
a) Fast and short term
b) Fast and long lasting
c) Slow and short term
d) Slow and long lasting
7. The feedback control mechanism is related
with
a) Bile secretion
b) HCl secretion
c) Hormonal secretion
d) Hering Breuer reflex
8. Pheromone is
a) A product of endocrine gland
b) Used for animal communication
c) Messenger RNA
d) Always protein
Simple Questions
9. Hormone is a/an
a) Enzyme
b) Chemical messenger
c) Excretory product
d) Glandular secretion
10. Hormones differ from enzymes as they are
a) Found in plants only
b) Found in animals only
c) Used up in metabolism
d) Not used in metabolism
11. Hormones of pituitary glands are
a) Proteins
b) Steroids
c) Some steroids and some proteins
d) Complex substances formed from
proteins, steroids and carbohydrates
12. Hormone secreted by pituitary gland is
chemically
a) All protein
b) All steroid
c) Complex compounds of proteins and
carbohydrates
d) Some steroids and some proteins
13. Hormone of hypothalamus are called
a) Regulatory hormones
b) Growth hormones
c) Tropic hormones
d) Both (a) and (c)
14. The structure and amino acid sequence of
the hormone insulin was discovered by
a) Benting b) Sanger
c) Pauling d) Cullen
15. W hich of the f ollowing is a
mineralocorticoid?
a) Testosterone b) Progesterone
c) Adrenaline d) Aldosterone
1. A heterocrine gland is one, which
a) Has two distinct parts
b) Serves a double function of exocrine and
endocrine gland
c) Produces two types of hormones
d) Occurs in two places
2. W hich gland is both exocrine and
endocrine?
a) Pancreas b) Thyroid
c) Pituitary d) Adrenal
3. Who is known as ‘Father of endocrinology’?
a) R.H Whittaker b) Pasteur
c) Einthoven d) Thomas Addison
4. First discovered hormone
a) Thyroxine b) Adrenaline
c) Secretin d) Insulin
5. Term ‘Hormone’ was coined by
a) WM Bayliss b) EH Schally
c) EH Starling d) GW Horris
6. Which of the following is true for the effect
of steroid hormone?
a) Fast and short term
b) Fast and long lasting
c) Slow and short term
d) Slow and long lasting
7. The feedback control mechanism is related
with
a) Bile secretion
b) HCl secretion
c) Hormonal secretion
d) Hering Breuer reflex
8. Pheromone is
a) A product of endocrine gland
b) Used for animal communication
c) Messenger RNA
d) Always protein
Simple Questions
9. Hormone is a/an
a) Enzyme
b) Chemical messenger
c) Excretory product
d) Glandular secretion
10. Hormones differ from enzymes as they are
a) Found in plants only
b) Found in animals only
c) Used up in metabolism
d) Not used in metabolism
11. Hormones of pituitary glands are
a) Proteins
b) Steroids
c) Some steroids and some proteins
d) Complex substances formed from
proteins, steroids and carbohydrates
12. Hormone secreted by pituitary gland is
chemically
a) All protein
b) All steroid
c) Complex compounds of proteins and
carbohydrates
d) Some steroids and some proteins
13. Hormone of hypothalamus are called
a) Regulatory hormones
b) Growth hormones
c) Tropic hormones
d) Both (a) and (c)
14. The structure and amino acid sequence of
the hormone insulin was discovered by
a) Benting b) Sanger
c) Pauling d) Cullen
15. W hich of the f ollowing is a
mineralocorticoid?
a) Testosterone b) Progesterone
c) Adrenaline d) Aldosterone
109
16. Which of the following is not a steroid
hormone?
a) Oestrogen b) Cortisone
c) Adrenaline d) Testosterone
17. A steroid hormone, which regulates glucose
metabolism is
a) Cortisol
b) Corticosterone
c) 11 deoxycorticosterone
d) Cortisone
18. Adrenaline and nor adrenaline are
hormones and act as
a) Energy producing agent
b) Food storage material
c) Neurotransmitter
d) Energy storing substances
19. Intercellular communication in multicellular
organisms occurs through
a) Digestive system only
b) Respiratory system only
c) Nervous system only
d) Both nervous and endocrine system
20. The ‘amino acid derivative’ among the
following hormone is
a) Insulin b) Epinephrine
c) Oestradiol d) Testosterone
21. Receptor of protein hormones are found
a) Inside nucleus b) Inside cytoplasm
c) On surface of ER d) On cell surface
22. The releasing hormones are produced by
a) Testis b) Pancreas
c) Pituitary d) Hypothalamus
23. Which one of the following is not a second
messenger in hormone action?
a) Sodium b) cAMP
c) cGMP d) Calcium
24. A peptide hormone produced by the anterior
pituitary is
a) Melatonin
b) Insulin
c) Estrogen
d) Progesterone
25. Which of the following is not necessarily a
property of all hormones?
a) Information carrying
b) Secreted in low amounts
c) Short half-life
d) Protein in nature
26. Why thyroxin is a hormone, not an enzyme
a) It is secreted in small quantity
b) It is not a polypeptide
c) It has no special effect
d) It is directly poured into blood
27. Which one of the following is not a second
messenger hormone action?
a) Calcium b) Sodium
c) cAMP d) cGMP
28. Which gland stores hormone in intercellular
space before its secretion into blood
a) Pancreas b) Thyroid
c) Testis d) Ovary
29. Which is a 32 amino acid water soluble
peptide hormone?
a) Gastrin b) Calcitonin
c) Glucagon d) Insulin
16. Which of the following is not a steroid
hormone?
a) Oestrogen b) Cortisone
c) Adrenaline d) Testosterone
17. A steroid hormone, which regulates glucose
metabolism is
a) Cortisol
b) Corticosterone
c) 11 deoxycorticosterone
d) Cortisone
18. Adrenaline and nor adrenaline are
hormones and act as
a) Energy producing agent
b) Food storage material
c) Neurotransmitter
d) Energy storing substances
19. Intercellular communication in multicellular
organisms occurs through
a) Digestive system only
b) Respiratory system only
c) Nervous system only
d) Both nervous and endocrine system
20. The ‘amino acid derivative’ among the
following hormone is
a) Insulin b) Epinephrine
c) Oestradiol d) Testosterone
21. Receptor of protein hormones are found
a) Inside nucleus b) Inside cytoplasm
c) On surface of ER d) On cell surface
22. The releasing hormones are produced by
a) Testis b) Pancreas
c) Pituitary d) Hypothalamus
23. Which one of the following is not a second
messenger in hormone action?
a) Sodium b) cAMP
c) cGMP d) Calcium
24. A peptide hormone produced by the anterior
pituitary is
a) Melatonin
b) Insulin
c) Estrogen
d) Progesterone
25. Which of the following is not necessarily a
property of all hormones?
a) Information carrying
b) Secreted in low amounts
c) Short half-life
d) Protein in nature
26. Why thyroxin is a hormone, not an enzyme
a) It is secreted in small quantity
b) It is not a polypeptide
c) It has no special effect
d) It is directly poured into blood
27. Which one of the following is not a second
messenger hormone action?
a) Calcium b) Sodium
c) cAMP d) cGMP
28. Which gland stores hormone in intercellular
space before its secretion into blood
a) Pancreas b) Thyroid
c) Testis d) Ovary
29. Which is a 32 amino acid water soluble
peptide hormone?
a) Gastrin b) Calcitonin
c) Glucagon d) Insulin
110
1. W hich of the following help in
communication with the other members of
the same species?
a) Hormones
b) Automones
c) Pheromones
d) Autocoids
2. One of the following is volatile
a) Enzymes b) Hormones
c) Pheromones d) All
3. Which of the following acts as both hormone
and enzyme
a) ADH hormone
b) Acetylcholine esterase
c) Angiotensinogen
d) Renin
4. W hich of the following acts as local
messenger?
a) Carrier protein
b) Glycoprotein
c) Phospholipid
d) Glycolipid
5. Sodium potassium pump is
a) A hormone b) An enzyme
c) A protein carrier d) An organelle
6. Metamorphosis in tadpole can be increased
by treatment of water with
a) NaCl b) Thyroxine
c) Iodine d) GH
7. Rate of hormone synthesis and secretion
depends upon
a) Functional efficiency of the feedback
system
b) Amount of excitation in target tissue
c) Degree of inhibition caused
d) Function state of the tissue/organ
8. Steroid hormones work as they
a) Enter into target cells and binds with
specific receptor and activates specific
genes to form protein
b) Bind to cell membrane
c) Catalyse formation of cAMP
d) None of the above
9. Which one hormone of the pituitary of the
rabbit controls the protein metabolism and
growth of skeleton?
a) Iodo thyroxin
b) Leutotrophic hormone
c) Somatotrophic hormone
d) Oxytosine
10. Who proposed the term ‘pheromone’?
a) Bergstrom b) Karlson
c) Starling d) Butendant
11. Which of these is not a ketone bodies
a) Acetoacetic acid
b) Succinic acid
c) Beta hydroxyl butyrate
d) Acetone
12. Which is an aminated hormone?
a) Progesterone b) Epinephrine
c) Oestrogen d) Relaxin
13. Who gave the molecular structure of
thyroxine hormone?
a) Gudernatsch
b) Kendall
c) WB Canon
d) Harrington and Barger
14. Appearance of facial hairs in a women
maybe due to the effect of
a) Temperature
b) Ultraviolet radiation
c) Hormone
d) Pollution
Difficult Questions
1. W hich of the following help in
communication with the other members of
the same species?
a) Hormones
b) Automones
c) Pheromones
d) Autocoids
2. One of the following is volatile
a) Enzymes b) Hormones
c) Pheromones d) All
3. Which of the following acts as both hormone
and enzyme
a) ADH hormone
b) Acetylcholine esterase
c) Angiotensinogen
d) Renin
4. W hich of the following acts as local
messenger?
a) Carrier protein
b) Glycoprotein
c) Phospholipid
d) Glycolipid
5. Sodium potassium pump is
a) A hormone b) An enzyme
c) A protein carrier d) An organelle
6. Metamorphosis in tadpole can be increased
by treatment of water with
a) NaCl b) Thyroxine
c) Iodine d) GH
7. Rate of hormone synthesis and secretion
depends upon
a) Functional efficiency of the feedback
system
b) Amount of excitation in target tissue
c) Degree of inhibition caused
d) Function state of the tissue/organ
8. Steroid hormones work as they
a) Enter into target cells and binds with
specific receptor and activates specific
genes to form protein
b) Bind to cell membrane
c) Catalyse formation of cAMP
d) None of the above
9. Which one hormone of the pituitary of the
rabbit controls the protein metabolism and
growth of skeleton?
a) Iodo thyroxin
b) Leutotrophic hormone
c) Somatotrophic hormone
d) Oxytosine
10. Who proposed the term ‘pheromone’?
a) Bergstrom b) Karlson
c) Starling d) Butendant
11. Which of these is not a ketone bodies
a) Acetoacetic acid
b) Succinic acid
c) Beta hydroxyl butyrate
d) Acetone
12. Which is an aminated hormone?
a) Progesterone b) Epinephrine
c) Oestrogen d) Relaxin
13. Who gave the molecular structure of
thyroxine hormone?
a) Gudernatsch
b) Kendall
c) WB Canon
d) Harrington and Barger
14. Appearance of facial hairs in a women
maybe due to the effect of
a) Temperature
b) Ultraviolet radiation
c) Hormone
d) Pollution
Difficult Questions
111
15. Which of the following statement is not
false?
a) Hormone produced in thyroid stimulates
metabolism
b) Hormone produced in ovary affects the
uterine contraction
c) Hormone produced in small intestine
stimulates heart
d) Hormone produced in adrenal cortex
stimulates heart beat
16. Hormones may be
a) Steroids
b) Peptides
c) Amino acid derivatives
d) All of these
17. If receptor molecule is removed from target
organ for hormone action, the target organ
will
a) Continue to respond but requires higher
concentration of hormone
b) Continue to respond but in opposite way
c) Continue to respond without any
difference
d) Not respond to hormone
18. Hormone produced in allergic reactions is
a) Glucocorticoid
b) Mineralocorticoid
c) Nor epinephrine
d) Epinephrine
19. The name second messenger is given to
a) ATP
b) cAMP
c) AMP
d) Both ATP and AMP
20. In heart cells, which one serves as a second
messenger, speeding up muscle cell
contraction in response to adrenaline?
a) cAMP b) cGMP
c) GTP d) ATP
21. Through negative feedback, a hormone may
shut off the secretion of an anterior pituitary
hormone by
a) Stimulating the release of a
(hypothalamic) releasing hormone
b) Inhibiting the release of a (hypothalamic)
inhibiting hormone
c) Inhibiting the release of a (hypothalamic)
releasing hormone
d) All of the above
22. In the homeostatic control of blood sugar
level, which organs function as modulator
and effector respectively?
a) Liver and islets of Langerhans
b) Hypothalamus and liver
c) Hypothalamus and islets of Langerhans
d) Islets of Langerhans and hypothalamus
23. Hormone produced more in dark is
a) Thyroxine b) Melatonin
c) Adrenaline d) Insulin
24. The secretion of aldosterone by adrenal
cortex is directly controlled by
a) Plasma K
+
concentration
b) Plasma Ca
+
concentration
c) Level of blood angiotensin
d) Both a and c are correct
25. Angiotensin is derived from plasma protein
“angiotensinogen’ by the action of rennin
and other nervous stimuli. Angiotensin
stimulates
a) Thyroid b) Adrenal
c) Ovary d) Thymus
15. Which of the following statement is not
false?
a) Hormone produced in thyroid stimulates
metabolism
b) Hormone produced in ovary affects the
uterine contraction
c) Hormone produced in small intestine
stimulates heart
d) Hormone produced in adrenal cortex
stimulates heart beat
16. Hormones may be
a) Steroids
b) Peptides
c) Amino acid derivatives
d) All of these
17. If receptor molecule is removed from target
organ for hormone action, the target organ
will
a) Continue to respond but requires higher
concentration of hormone
b) Continue to respond but in opposite way
c) Continue to respond without any
difference
d) Not respond to hormone
18. Hormone produced in allergic reactions is
a) Glucocorticoid
b) Mineralocorticoid
c) Nor epinephrine
d) Epinephrine
19. The name second messenger is given to
a) ATP
b) cAMP
c) AMP
d) Both ATP and AMP
20. In heart cells, which one serves as a second
messenger, speeding up muscle cell
contraction in response to adrenaline?
a) cAMP b) cGMP
c) GTP d) ATP
21. Through negative feedback, a hormone may
shut off the secretion of an anterior pituitary
hormone by
a) Stimulating the release of a
(hypothalamic) releasing hormone
b) Inhibiting the release of a (hypothalamic)
inhibiting hormone
c) Inhibiting the release of a (hypothalamic)
releasing hormone
d) All of the above
22. In the homeostatic control of blood sugar
level, which organs function as modulator
and effector respectively?
a) Liver and islets of Langerhans
b) Hypothalamus and liver
c) Hypothalamus and islets of Langerhans
d) Islets of Langerhans and hypothalamus
23. Hormone produced more in dark is
a) Thyroxine b) Melatonin
c) Adrenaline d) Insulin
24. The secretion of aldosterone by adrenal
cortex is directly controlled by
a) Plasma K
+
concentration
b) Plasma Ca
+
concentration
c) Level of blood angiotensin
d) Both a and c are correct
25. Angiotensin is derived from plasma protein
“angiotensinogen’ by the action of rennin
and other nervous stimuli. Angiotensin
stimulates
a) Thyroid b) Adrenal
c) Ovary d) Thymus
112
26. Which of the following statement is correct
in relation to the endocrine system?
a) Adenohypophysis is under direct neural
regulation of the hypothalamus
b) Organs in the body like gastrointestinal
tract, heart, kidney and liver do not
produce any hormones
c) Non nutrient chemicals produced by the
body in trace amount that act as
intercellular messenger are known as
hormones
d) Releasing and inhibitory hormones are
produced by the pituitary gland
27. Which one of the following statements about
the particular entity is true?
a) The gene for producing insulin is present
in every body cell
b) Nucleosome is formed of nucleotides
c) DNA consists of a core of eight histones
d) Centromere is found in animals cells,
which produces aster during cell division
28. Lacrimal glands are concerned with the
secretion of
a) Hormones b) Digestive juices
c) Enzymes d) Tears
ANSWER KEYS
Simple Questions
1.b 2.a 3.d 4.c 5.c 6.d 7.c 8.b 9.b 10.c 11.a 12.a
13.d 14.b 15.d 16.c 17.a 18.c 19.d 20.b 21.d 22.d 23.a 24.a\
25.d 26.d 27.d 28.b 29.b 30.c
Difficult Questions
1.c 2.c 3.d 4.a 5.c 6.c 7.a 8.a 9.c 10.b 11.b 12.b
13.d 14.c 15.a 16.d 17.d 18.a 19.b 20.a 21.c 22.c 23.b 24.a
25.b 26.c 27.a 28.d
26. Which of the following statement is correct
in relation to the endocrine system?
a) Adenohypophysis is under direct neural
regulation of the hypothalamus
b) Organs in the body like gastrointestinal
tract, heart, kidney and liver do not
produce any hormones
c) Non nutrient chemicals produced by the
body in trace amount that act as
intercellular messenger are known as
hormones
d) Releasing and inhibitory hormones are
produced by the pituitary gland
27. Which one of the following statements about
the particular entity is true?
a) The gene for producing insulin is present
in every body cell
b) Nucleosome is formed of nucleotides
c) DNA consists of a core of eight histones
d) Centromere is found in animals cells,
which produces aster during cell division
28. Lacrimal glands are concerned with the
secretion of
a) Hormones b) Digestive juices
c) Enzymes d) Tears
ANSWER KEYS
Simple Questions
1.b 2.a 3.d 4.c 5.c 6.d 7.c 8.b 9.b 10.c 11.a 12.a
13.d 14.b 15.d 16.c 17.a 18.c 19.d 20.b 21.d 22.d 23.a 24.a\
25.d 26.d 27.d 28.b 29.b 30.c
Difficult Questions
1.c 2.c 3.d 4.a 5.c 6.c 7.a 8.a 9.c 10.b 11.b 12.b
13.d 14.c 15.a 16.d 17.d 18.a 19.b 20.a 21.c 22.c 23.b 24.a
25.b 26.c 27.a 28.d
113
1. Hormones are
a) Internal secretion mostly discharged in
the blood by endocrine glands
b) Secretion of exocrine glands
c) Chemical substances secreted into the
gut
d) Inorganic catalyst
2. During emergency, which of the following
hormone is secreted?
a) Aldosterone b) Thyroxine
c) Adrenaline d) Calcitonin
3. Term “Hormone” was coined by
a) W.M Baylis b) E.H Schally
c) E.H.Starling d) Harris
4. Who is known as “father of endocrinology”?
a) R.H.Whittakar b) Pasteur
c) Einthoven d) Thomas Addison
5. A group of compounds now recognised as
local hormones are
a) Prostaglandins b) Prostacyclins
c) Cytokinins d) Substance ‘P’
DPP - 4
6. W hich of the following is secondary
messenger?
a) ATP b) Cyclic AMP
c) GTP d) ATP and AMP
7. Calcitonin is a thyroid hormone which
a) Elevates potassium level in blood
b) Lowers calcium level in blood
c) Elevates calcium level in blood
d) Has no effect on calcium
8. Pheromones secreted by
a) Endocrine gland
b) Exocrine gland
c) Apocrine glands
d) Mixed gland
9. Hormones are produced by
a) Exocrine glands
b) Endocrine glands
c) Holocrine glands
d) Apocrine glands
10. “Secondary messenger” is
a) Cyclic AMP b) ATP
c) ADP d) DNA
1. Hormones are
a) Internal secretion mostly discharged in
the blood by endocrine glands
b) Secretion of exocrine glands
c) Chemical substances secreted into the
gut
d) Inorganic catalyst
2. During emergency, which of the following
hormone is secreted?
a) Aldosterone b) Thyroxine
c) Adrenaline d) Calcitonin
3. Term “Hormone” was coined by
a) W.M Baylis b) E.H Schally
c) E.H.Starling d) Harris
4. Who is known as “father of endocrinology”?
a) R.H.Whittakar b) Pasteur
c) Einthoven d) Thomas Addison
5. A group of compounds now recognised as
local hormones are
a) Prostaglandins b) Prostacyclins
c) Cytokinins d) Substance ‘P’
DPP - 4
6. W hich of the following is secondary
messenger?
a) ATP b) Cyclic AMP
c) GTP d) ATP and AMP
7. Calcitonin is a thyroid hormone which
a) Elevates potassium level in blood
b) Lowers calcium level in blood
c) Elevates calcium level in blood
d) Has no effect on calcium
8. Pheromones secreted by
a) Endocrine gland
b) Exocrine gland
c) Apocrine glands
d) Mixed gland
9. Hormones are produced by
a) Exocrine glands
b) Endocrine glands
c) Holocrine glands
d) Apocrine glands
10. “Secondary messenger” is
a) Cyclic AMP b) ATP
c) ADP d) DNA
114
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid gland
Posterior view
Thymus gland
Stomach
Adrenal glands
Adipose tissue
Small intestine
Testes
(male)
Ovaries (female)
ENDOCRINE GLANDS
Pancreas
Kidney
5.1 PITUITARY GLAND AND HYPOTHALAMUS
HYPOTHALAMUS
The neurosecretory cells of hypothalamus produce releasing factors in very small amount which
are as follows:
PITUITARY GLAND
5.1.1 Gross anatomy
The pituitary gland, also called the hypophysis, is a small gland, about 1 cm in diameter and 0.5-1
g in weight that lies in the sella turcica, a bony cavity at the base of the brain, and is connected to
UNIT 5 - ENDOCRINE SYSTEM II
Hormones Major functions Chemical
Structure
Thyrotropin releasing hormone (TRH) Stimulates secretion of TSH and Peptide
prolactin
Corticotropin releasing hormone (CRH) Causes release of ACTH Peptide
Growth hormone releasing hormone (GHRH) Causes release of growth hormone Peptide
Growth hormone inhibitory hormone (GHIH) Inhibits release of growth hormone Peptide
(somatostatin)
Gonadotropin releasing hormone (GnRH) Causes release of LH and FSH
Dopamine or prolactin inhibiting factor (PIF) Inhibits release of prolactin Amine
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid gland
Posterior view
Thymus gland
Stomach
Adrenal glands
Adipose tissue
Small intestine
Testes
(male)
Ovaries (female)
ENDOCRINE GLANDS
Pancreas
Kidney
5.1 PITUITARY GLAND AND HYPOTHALAMUS
HYPOTHALAMUS
The neurosecretory cells of hypothalamus produce releasing factors in very small amount which
are as follows:
PITUITARY GLAND
5.1.1 Gross anatomy
The pituitary gland, also called the hypophysis, is a small gland, about 1 cm in diameter and 0.5-1
g in weight that lies in the sella turcica, a bony cavity at the base of the brain, and is connected to
UNIT 5 - ENDOCRINE SYSTEM II
Hormones Major functions Chemical
Structure
Thyrotropin releasing hormone (TRH) Stimulates secretion of TSH and Peptide
prolactin
Corticotropin releasing hormone (CRH) Causes release of ACTH Peptide
Growth hormone releasing hormone (GHRH) Causes release of growth hormone Peptide
Growth hormone inhibitory hormone (GHIH) Inhibits release of growth hormone Peptide
(somatostatin)
Gonadotropin releasing hormone (GnRH) Causes release of LH and FSH
Dopamine or prolactin inhibiting factor (PIF) Inhibits release of prolactin Amine
115
the hypothalamus by the pituitary (or hypophysial) stalk also called as infundibulum. The upper
terminal end of infundibulum which is attached to the hypothalamus is called tubercinerium/median
eminence. The lower terminal end of infundibulum is bulging type and called posterior lobe or
pars nervosa.
Physiologically, the pituitary gland is divisible into two distinct portions: the anterior pituitary, also
known as the adenohypophysis, and the posterior pituitary, also known as the neurohypophysis.
Between these is a small, relatively avascular zone called the pars intermedia, which is almost
absent in the human being but is much larger and much more functional in some lower animals. In
males, it is in the form of a thin membrane only and is inactive.
Embryologically, the two portions of the pituitary originate from different sources: the anterior pituitary
from Rathke’s pouch, which is an embryonic invagination of the pharyngeal epithelium, and the
posterior pituitary from a neural tissue outgrowth from the hypothalamus. The origin of the anterior
pituitary from the pharyngeal epithelium explains the epithelioid nature of its cells, and the origin of
the posterior pituitary from neural tissue explains the presence of large numbers of glial-type cells in
this gland. Foetal gut develops into alimentary canal; the anterior part of gut is called stomodaeum
(developed from ectoderm). A small projection develops from dorsal surface of stomodaeum and
forms the Rathke’s pouch.
Hypothalamic
neurons in the
supraoptic nuclei
Superior
hypophyseal
artery
Hypophyseal portal system
•Primary capillary plexus
•Hypophyseal portal veins
•Secondary capillary plexus
Anterior lobe
Secretory cells of
adenohypophysis
TSH, FSH, LH, ACTH, GH, PRL
Inferior
hypophyseal
artery
Oxytocin ADH
Venule
Posterior
lobe
Neurohypophysis
(storage area for
hypothalamic
hormones)
Hypothalamic-
hypophyseal tract
Infundibulum
(connecting stalk)
Neurons in the ventral hypothalamus
Hypothalamic
neurons in the
paraventricular nuclei
the hypothalamus by the pituitary (or hypophysial) stalk also called as infundibulum. The upper
terminal end of infundibulum which is attached to the hypothalamus is called tubercinerium/median
eminence. The lower terminal end of infundibulum is bulging type and called posterior lobe or
pars nervosa.
Physiologically, the pituitary gland is divisible into two distinct portions: the anterior pituitary, also
known as the adenohypophysis, and the posterior pituitary, also known as the neurohypophysis.
Between these is a small, relatively avascular zone called the pars intermedia, which is almost
absent in the human being but is much larger and much more functional in some lower animals. In
males, it is in the form of a thin membrane only and is inactive.
Embryologically, the two portions of the pituitary originate from different sources: the anterior pituitary
from Rathke’s pouch, which is an embryonic invagination of the pharyngeal epithelium, and the
posterior pituitary from a neural tissue outgrowth from the hypothalamus. The origin of the anterior
pituitary from the pharyngeal epithelium explains the epithelioid nature of its cells, and the origin of
the posterior pituitary from neural tissue explains the presence of large numbers of glial-type cells in
this gland. Foetal gut develops into alimentary canal; the anterior part of gut is called stomodaeum
(developed from ectoderm). A small projection develops from dorsal surface of stomodaeum and
forms the Rathke’s pouch.
Hypothalamic
neurons in the
supraoptic nuclei
Superior
hypophyseal
artery
Hypophyseal portal system
•Primary capillary plexus
•Hypophyseal portal veins
•Secondary capillary plexus
Anterior lobe
Secretory cells of
adenohypophysis
TSH, FSH, LH, ACTH, GH, PRL
Inferior
hypophyseal
artery
Oxytocin ADH
Venule
Posterior
lobe
Neurohypophysis
(storage area for
hypothalamic
hormones)
Hypothalamic-
hypophyseal tract
Infundibulum
(connecting stalk)
Neurons in the ventral hypothalamus
Hypothalamic
neurons in the
paraventricular nuclei
116
Hypophysis cerebri or pituitary body = Neurohypophysis + Adenohypophysis
Hypophysis recess: A remaining and vestigial cavity of Rathke’s pouch found in the anterior lobe
Superior branch of hypophyseal artery supplies blood to the hypothalamus while the inferior
branch of hypophyseal artery supplies blood to the pituitary gland. Hypophyseal portal vein
collects the blood from hypothalamus and supplies to the pituitary gland.
Posterior lobe of pituitary gland is 1/4th part of the total gland. It is just like nervous tissue, because
in it, the terminal ends of the axons of neurosecretory cells of hypothalamus are swollen. These
swollen ends are called Herring bodies and hormones are released in these bodies. Pituicytes
are large, branched fatty neuroglial supporting cells in between axons.
Hormones that control the release of another hormone from an endocrine gland are called tropic
hormones. The anterior pituitary secretes seven different peptide or protein hormones: growth
hormone (GH), prolactin (PRL), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone
(ATCH), follicle-stimulating hormone (FSH), luteinizing hormone (LH) and melanocyte stimulating
hormone (MSH). The posterior pituitary releases antidiuretic hormone (ADH) (also known as
vasopressin) and oxytocin.
5.1.2 Hormones secreted by adenohypophysis
A. Growth hormone (GH) or Somatotropic/Somatotropin hormone (STH)
Somatotropes produce STH that stimulates body growth and metabolism.
STH increases the longitudinal length of bones, stimulates muscle and cartilage growth by increasing
collagen synthesis and promotes mitosis and increases cells in many organs and tissue eg. liver.
STH increases lipolysis so that free fatty acid level of plasma rises. Fat is used for energy in preference
to carbohydrate and protein, due to this protein deposition increases. Hyperglycaemia develops due
to decreased uptake of glucose in cells, so STH is also called diabetogenic hormone. STH increases
the amino acid uptake by liver & muscle cells & helps in protein synthesis.
In presence of thyroxin and insulin, GH become more active and help in body growth.
Hyposecretion: STH deficiency in childhood or adolescence causes dwarfism. Dwarfism due to
the defect of pituitary is Ateliosis. Midgets, clowns of circus are such dwarfs, they are physically &
mentally normal while sexual maturation is delayed.
Hypersecretion: STH hypersecretion cause higher amino acid supply to the body cells. Epiphyseal
cartilage present on the edges of bones does not convert into bone for a long time. Thus the bones
of legs & hands become very long and height increases very much causing imbalance. This disease
is called Gigantism. STH hypersecretion in adulthood lengthens the jaw bones of the affected
person, cheek bones bulge out, broad hands, legs & fingers of person becomes gorilla like. These
symptoms are attributed to acromegaly.
B. Luteotrophic/Prolactin/Lactogenic/Mammotrophin hormone (PRL)
Lactotropes, mammotropes secrete PRL.
Hypophysis cerebri or pituitary body = Neurohypophysis + Adenohypophysis
Hypophysis recess: A remaining and vestigial cavity of Rathke’s pouch found in the anterior lobe
Superior branch of hypophyseal artery supplies blood to the hypothalamus while the inferior
branch of hypophyseal artery supplies blood to the pituitary gland. Hypophyseal portal vein
collects the blood from hypothalamus and supplies to the pituitary gland.
Posterior lobe of pituitary gland is 1/4th part of the total gland. It is just like nervous tissue, because
in it, the terminal ends of the axons of neurosecretory cells of hypothalamus are swollen. These
swollen ends are called Herring bodies and hormones are released in these bodies. Pituicytes
are large, branched fatty neuroglial supporting cells in between axons.
Hormones that control the release of another hormone from an endocrine gland are called tropic
hormones. The anterior pituitary secretes seven different peptide or protein hormones: growth
hormone (GH), prolactin (PRL), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone
(ATCH), follicle-stimulating hormone (FSH), luteinizing hormone (LH) and melanocyte stimulating
hormone (MSH). The posterior pituitary releases antidiuretic hormone (ADH) (also known as
vasopressin) and oxytocin.
5.1.2 Hormones secreted by adenohypophysis
A. Growth hormone (GH) or Somatotropic/Somatotropin hormone (STH)
Somatotropes produce STH that stimulates body growth and metabolism.
STH increases the longitudinal length of bones, stimulates muscle and cartilage growth by increasing
collagen synthesis and promotes mitosis and increases cells in many organs and tissue eg. liver.
STH increases lipolysis so that free fatty acid level of plasma rises. Fat is used for energy in preference
to carbohydrate and protein, due to this protein deposition increases. Hyperglycaemia develops due
to decreased uptake of glucose in cells, so STH is also called diabetogenic hormone. STH increases
the amino acid uptake by liver & muscle cells & helps in protein synthesis.
In presence of thyroxin and insulin, GH become more active and help in body growth.
Hyposecretion: STH deficiency in childhood or adolescence causes dwarfism. Dwarfism due to
the defect of pituitary is Ateliosis. Midgets, clowns of circus are such dwarfs, they are physically &
mentally normal while sexual maturation is delayed.
Hypersecretion: STH hypersecretion cause higher amino acid supply to the body cells. Epiphyseal
cartilage present on the edges of bones does not convert into bone for a long time. Thus the bones
of legs & hands become very long and height increases very much causing imbalance. This disease
is called Gigantism. STH hypersecretion in adulthood lengthens the jaw bones of the affected
person, cheek bones bulge out, broad hands, legs & fingers of person becomes gorilla like. These
symptoms are attributed to acromegaly.
B. Luteotrophic/Prolactin/Lactogenic/Mammotrophin hormone (PRL)
Lactotropes, mammotropes secrete PRL.
117
Lactation (Galactopoiesis): PRL causes lactation after delivery. Breast is prepared for lactation by
estrogen (duct growth) and progesterone (lobule growth) but both these hormones inhibit the actual
secretion of milk.
Hypothalamus mainly stimulates the production of all pituitary hormones, but it inhibits PRL production
because normally hypothalamus-prolactin-inhibitory hormone (Dopamine) is greater than the releasing
hormone. Dopamine is a catecholamine and neurotransmitter in the hypothalamus.
During pregnancy, PRL steadily increase until term but due to high level of estrogen and progesterone
(secreted by placenta) lactation is inhibited. After expulsion of the placenta at parturition, there is an
abrupt decline in circulating estrogen and progesterone. The drop of circulating estrogen initiates
lactation. Nursing stimulates PRL secretion that inhibits the action of GnRH on pituitary and
antagonizes the action of gonadotropin on the ovaries. Ovulation is inhibited and the ovaries become
inactive.
Nursing is an important and effective method of birth control.
C. Thyrotrophic/Thyroid stimulating hormone (TTH/TSH)
TSH is secreted by thyrotropes (basophil cells). It is glycoprotein in nature and stimulates the thyroid
gland to secrete thyroxine. TSH causes growth of the thyroid gland.
Secretion of TSH is stimulated by thyrotrophin releasing factor and inhibited by somatostatin of
hypothalamus.
D. Adrenocorticotropic hormone or corticotropine (ACTH)
ACTH is secreted by corticotropes. In man, ACTH has valine and tyrosine more in quantity. It
accelerates the cortex part of adrenal gland to secrete hormones.
E. Follicle-stimulating hormone (FSH)
Gonadotropes secrete FSH. It is a glycoprotein and is secreted in both males and females. It
stimulates spermatogenesis and normal functioning of seminiferous tubules in males while in females,
it stimulates oogenesis and development of Graafian follicles in ovary. FSH is also known as
gametokinetic factor. Estrogen secreted by Graafian follicles is also affected by FSH.
F. Luteinizing hormone (LH) or Interstitial cell stimulating hormone (ICSH)
Gonadotropes also secrete LH. It is also a glycoprotein, and stimulates ovulation in females to form
the corpus luteum. Progesterone, secreted by corpus luteum is stimulated by LH. In males, LH is
called ICSH as it affects the Leydig cells or interstitial cells of testes to stimulate the secretion of
testosterone. LH is also called gamete releasing factor.
FSH and LH together are called gonadotrophic hormone (GTH) or Synergesic hormone as they act
in combined form. GTH secretion starts secreting during puberty and their secretion is regulated by
hypothalamus. It is supposed that there is a biological clock present to control all this.
Lactation (Galactopoiesis): PRL causes lactation after delivery. Breast is prepared for lactation by
estrogen (duct growth) and progesterone (lobule growth) but both these hormones inhibit the actual
secretion of milk.
Hypothalamus mainly stimulates the production of all pituitary hormones, but it inhibits PRL production
because normally hypothalamus-prolactin-inhibitory hormone (Dopamine) is greater than the releasing
hormone. Dopamine is a catecholamine and neurotransmitter in the hypothalamus.
During pregnancy, PRL steadily increase until term but due to high level of estrogen and progesterone
(secreted by placenta) lactation is inhibited. After expulsion of the placenta at parturition, there is an
abrupt decline in circulating estrogen and progesterone. The drop of circulating estrogen initiates
lactation. Nursing stimulates PRL secretion that inhibits the action of GnRH on pituitary and
antagonizes the action of gonadotropin on the ovaries. Ovulation is inhibited and the ovaries become
inactive.
Nursing is an important and effective method of birth control.
C. Thyrotrophic/Thyroid stimulating hormone (TTH/TSH)
TSH is secreted by thyrotropes (basophil cells). It is glycoprotein in nature and stimulates the thyroid
gland to secrete thyroxine. TSH causes growth of the thyroid gland.
Secretion of TSH is stimulated by thyrotrophin releasing factor and inhibited by somatostatin of
hypothalamus.
D. Adrenocorticotropic hormone or corticotropine (ACTH)
ACTH is secreted by corticotropes. In man, ACTH has valine and tyrosine more in quantity. It
accelerates the cortex part of adrenal gland to secrete hormones.
E. Follicle-stimulating hormone (FSH)
Gonadotropes secrete FSH. It is a glycoprotein and is secreted in both males and females. It
stimulates spermatogenesis and normal functioning of seminiferous tubules in males while in females,
it stimulates oogenesis and development of Graafian follicles in ovary. FSH is also known as
gametokinetic factor. Estrogen secreted by Graafian follicles is also affected by FSH.
F. Luteinizing hormone (LH) or Interstitial cell stimulating hormone (ICSH)
Gonadotropes also secrete LH. It is also a glycoprotein, and stimulates ovulation in females to form
the corpus luteum. Progesterone, secreted by corpus luteum is stimulated by LH. In males, LH is
called ICSH as it affects the Leydig cells or interstitial cells of testes to stimulate the secretion of
testosterone. LH is also called gamete releasing factor.
FSH and LH together are called gonadotrophic hormone (GTH) or Synergesic hormone as they act
in combined form. GTH secretion starts secreting during puberty and their secretion is regulated by
hypothalamus. It is supposed that there is a biological clock present to control all this.
118
G. Melanocyte stimulating hormone (MSH)
MSH is secreted by the corticotropes of middle lobe, pars intermedia, also called Intermedin. In
males, MSH is secreted by anterior lobe, as middle lobe is not well developed. It stimulates the
melanocytes to synthesize melanin in mammals. MSH is related with the change in colour of skin in
amphibians and reptiles; this phenomenon of color changing is metachrosis. It darkens the
complexion by distributing melanin evenly under the skin. Just opposite to it, melatonin secreted by
pineal body, collects the melanin pigments at one place thus fairing the complexion.
MSH is found in all the vertebrates, but it is functional in poikilothermic animals e.g. Fishes,
amphibians, reptiles etc.
5.1.3 Hormones secreted by neurohypophysis
Posterior lobe hormones are not synthesized in the gland itself but in the supraoptic nuclei and
paraventricular nuclei of hypothalamus. The hormones are then transported from their origin to
posterior pituitary through axons of hypothlamo-hypophyseal tract and stored in association with
proteins neurophysin-I and neurophysin-II.
A. Vasopressin/Pitressin/Anti-diuretic hormone (ADH)
ADH increases reabsorption of water in collecting ducts and in DCT, and reduces the amount of
urine. It also increases the blood pressure.
Hyposecretion: The amount of urine increases, process is called diuresis.
Diabetes insipidus: Patient is excessively thirsty, dehydration starts in the body and excrete
lots of dilute urine (tasteless, polyuria).
Deficiency of water starts in extracellular fluid (ECF), blood pressure reduces, urine becomes
dilute and blood becomes thick or concentrated. Intake of coffee, tea and excess alcohol etc.
decrease ADH secretion. Secretion is maximum in animals of xerophytic region eg. camel.
Hypersecretion: Causes dilution of blood and increases urine concentration increasing BP. Kangaroo
rat (Dipodomys) also shows hypersecretion of ADH and never drinks water in its lifetime.
B. Oxytocin/Pitocin
Secreted by the pituitary glands of mother at the time of parturition, thus the main parturition
hormone. It stimulates rapid contractions and expansions of non-striated muscles of the uterine
wall at the last stage of gestation period (pregnancy) causing labor pains just before child birth.
Oxytocin also initiates uterine wall contractions during copulation to sweep out semen in the fallopian
tubes.
Oxytocin contracts the myoepithelial cells present at all sides of alveoli of mammary glands and
assist in milk ejection, also called milk let-down hormone.
In females, oxytocin is also related with emotion. Even thought, cry or sound of baby can bring
about release of this hormone in lactating mother.
Oxytocin helps during egg-laying in birds. Injection of oxytocin stimulates in cows and buffaloes for
instant milk release.
G. Melanocyte stimulating hormone (MSH)
MSH is secreted by the corticotropes of middle lobe, pars intermedia, also called Intermedin. In
males, MSH is secreted by anterior lobe, as middle lobe is not well developed. It stimulates the
melanocytes to synthesize melanin in mammals. MSH is related with the change in colour of skin in
amphibians and reptiles; this phenomenon of color changing is metachrosis. It darkens the
complexion by distributing melanin evenly under the skin. Just opposite to it, melatonin secreted by
pineal body, collects the melanin pigments at one place thus fairing the complexion.
MSH is found in all the vertebrates, but it is functional in poikilothermic animals e.g. Fishes,
amphibians, reptiles etc.
5.1.3 Hormones secreted by neurohypophysis
Posterior lobe hormones are not synthesized in the gland itself but in the supraoptic nuclei and
paraventricular nuclei of hypothalamus. The hormones are then transported from their origin to
posterior pituitary through axons of hypothlamo-hypophyseal tract and stored in association with
proteins neurophysin-I and neurophysin-II.
A. Vasopressin/Pitressin/Anti-diuretic hormone (ADH)
ADH increases reabsorption of water in collecting ducts and in DCT, and reduces the amount of
urine. It also increases the blood pressure.
Hyposecretion: The amount of urine increases, process is called diuresis.
Diabetes insipidus: Patient is excessively thirsty, dehydration starts in the body and excrete
lots of dilute urine (tasteless, polyuria).
Deficiency of water starts in extracellular fluid (ECF), blood pressure reduces, urine becomes
dilute and blood becomes thick or concentrated. Intake of coffee, tea and excess alcohol etc.
decrease ADH secretion. Secretion is maximum in animals of xerophytic region eg. camel.
Hypersecretion: Causes dilution of blood and increases urine concentration increasing BP. Kangaroo
rat (Dipodomys) also shows hypersecretion of ADH and never drinks water in its lifetime.
B. Oxytocin/Pitocin
Secreted by the pituitary glands of mother at the time of parturition, thus the main parturition
hormone. It stimulates rapid contractions and expansions of non-striated muscles of the uterine
wall at the last stage of gestation period (pregnancy) causing labor pains just before child birth.
Oxytocin also initiates uterine wall contractions during copulation to sweep out semen in the fallopian
tubes.
Oxytocin contracts the myoepithelial cells present at all sides of alveoli of mammary glands and
assist in milk ejection, also called milk let-down hormone.
In females, oxytocin is also related with emotion. Even thought, cry or sound of baby can bring
about release of this hormone in lactating mother.
Oxytocin helps during egg-laying in birds. Injection of oxytocin stimulates in cows and buffaloes for
instant milk release.
119
Hypothalamus
Indirect control through release of regulatory hormones
CRHTRHGH-RH GH-IH PRF PIH GnRH
Direct release of hormones
Sensory
stimulation
Osmoreceptor stimulation
Regulatory hormones are released into
the hypophyseal protal system for delivery
to the anterior lobe of the pituitary gland.
Adrenal cortex
Anterior lobe of
pituitary gland
ACTH
Adrenal glands
Thyroid
gland
TSHGH
Liver
Somatomedins
PRL
Glucocorticoids (steroid
hormones)
Thyroid hormones
Bone, muscle, other tissues
Mammary
glands
Testes
of male
Ovaries
of female
Melanocytes (uncertain
in healthy adults)significance
Females: Uterine smooth
muscle and mammary glands
Males: Smooth muscle in ductus deferens and
prostate gland
Kidneys
InhibinTestosteroneEstrogenProgesteroneInhibin
FSHLH
MSH
OXT
ADH
Posterior lobe
of pituitary gland
5.2 PINEAL GLAND
The pineal gland is located between the cerebral hemispheres of the brain. It is attached to the
roof of the third ventricle in the diencephalon. The pineal gland consists of secretory cells, called
pinealocytes, that secrete the hormone melatonin. Melatonin is derived from serotonin (a
neuropeptide) and is regulated in response to the light and dark of the environment (the diurnal
cycle). Photons, packet of light, are detected by the retinas of the eyes, which initiate a nerve
impulse that is detected by the pineal gland. This mechanism is similar to the process in the posterior
pituitary or adrenal medulla. The pineal gland synthesizes the highest levels of melatonin during the
night, when light levels are the lowest, and the increased blood concentrations of melatonin makes
us sleepy. Blood concentrations of melatonin are lowest during the day, when light exposure inhibits
the synthesis of the hormone.
The target cells of melatonin are located in the suprachiasmati nucleus (SCN) of the brain. The
SCN functions as a biological clock that regulates physiological processes such as the sleep wake
cycle, appetite, and body temperature. Melatonin is thought to inhibit the release of gonadotropins
from the anterior pituitary, which affect the onset of puberty.
Hypothalamus
Indirect control through release of regulatory hormones
CRHTRHGH-RH GH-IH PRF PIH GnRH
Direct release of hormones
Sensory
stimulation
Osmoreceptor stimulation
Regulatory hormones are released into
the hypophyseal protal system for delivery
to the anterior lobe of the pituitary gland.
Adrenal cortex
Anterior lobe of
pituitary gland
ACTH
Adrenal glands
Thyroid
gland
TSHGH
Liver
Somatomedins
PRL
Glucocorticoids (steroid
hormones)
Thyroid hormones
Bone, muscle, other tissues
Mammary
glands
Testes
of male
Ovaries
of female
Melanocytes (uncertain
in healthy adults)significance
Females: Uterine smooth
muscle and mammary glands
Males: Smooth muscle in ductus deferens and
prostate gland
Kidneys
InhibinTestosteroneEstrogenProgesteroneInhibin
FSHLH
MSH
OXT
ADH
Posterior lobe
of pituitary gland
5.2 PINEAL GLAND
The pineal gland is located between the cerebral hemispheres of the brain. It is attached to the
roof of the third ventricle in the diencephalon. The pineal gland consists of secretory cells, called
pinealocytes, that secrete the hormone melatonin. Melatonin is derived from serotonin (a
neuropeptide) and is regulated in response to the light and dark of the environment (the diurnal
cycle). Photons, packet of light, are detected by the retinas of the eyes, which initiate a nerve
impulse that is detected by the pineal gland. This mechanism is similar to the process in the posterior
pituitary or adrenal medulla. The pineal gland synthesizes the highest levels of melatonin during the
night, when light levels are the lowest, and the increased blood concentrations of melatonin makes
us sleepy. Blood concentrations of melatonin are lowest during the day, when light exposure inhibits
the synthesis of the hormone.
The target cells of melatonin are located in the suprachiasmati nucleus (SCN) of the brain. The
SCN functions as a biological clock that regulates physiological processes such as the sleep wake
cycle, appetite, and body temperature. Melatonin is thought to inhibit the release of gonadotropins
from the anterior pituitary, which affect the onset of puberty.
120
Higher melatonin levels at night make us sleepy, and a disruption in melatonin synthesis can disrupt
the sleep cycle. Travel across several time zones can result in disruptions to the sleep cycle, or jet
lag. This is due to the change in the dark light cycle that the body is accustomed to, and it can take
several days for melatonin synthesis to adapt to the change. Melatonin supplements are available
to treat jet lag as well as other sleep disorders; however, their efficacy has not been conclusively
established.
Melatonin is functional in lower vertebrates only. In amphibians and reptiles, it is related with
metachrosis and affects the melanophores of skin, thus acts antagonistically to the MSH of pituitary
i.e. it fairs the complexion of skin.
Melatonin also influences metabolism, pigmentation, menstrual cycle and defense capability.
Mid-part of gland secretes antigonadial hormone and controls the sexual behavior in mammals. It
inhibits sexual irritation, and the development of genitalia and their functions.
Maximum development of pineal body is up to 7 years and then it undergoes involution and at 14
years age, interstitial tissue and crystals of CaCO
3
or Ca
3
PO
4
are deposited in it, thus are called
brain sand or Acervuli.
Night
(dark period)
Day
(light period)
Superior cervical ganglion
Suprachiasmatic
nucleus (SCN)
Stimulation
Inhibition
Pineal gland
HN
OH C
3
H
N
Melatonin
O
CH
3
TARGET POINTS
Pineal gland is also known as epiphysis cerebri as it is a part of brain. It is ectodermal in
origin.
It is called third eye in frog.
If pineal body is removed from rats, these will attain premature adolescence.
Children blind from birth attain puberty earlier than normal.
Higher melatonin levels at night make us sleepy, and a disruption in melatonin synthesis can disrupt
the sleep cycle. Travel across several time zones can result in disruptions to the sleep cycle, or jet
lag. This is due to the change in the dark light cycle that the body is accustomed to, and it can take
several days for melatonin synthesis to adapt to the change. Melatonin supplements are available
to treat jet lag as well as other sleep disorders; however, their efficacy has not been conclusively
established.
Melatonin is functional in lower vertebrates only. In amphibians and reptiles, it is related with
metachrosis and affects the melanophores of skin, thus acts antagonistically to the MSH of pituitary
i.e. it fairs the complexion of skin.
Melatonin also influences metabolism, pigmentation, menstrual cycle and defense capability.
Mid-part of gland secretes antigonadial hormone and controls the sexual behavior in mammals. It
inhibits sexual irritation, and the development of genitalia and their functions.
Maximum development of pineal body is up to 7 years and then it undergoes involution and at 14
years age, interstitial tissue and crystals of CaCO
3
or Ca
3
PO
4
are deposited in it, thus are called
brain sand or Acervuli.
Night
(dark period)
Day
(light period)
Superior cervical ganglion
Suprachiasmatic
nucleus (SCN)
Stimulation
Inhibition
Pineal gland
HN
OH C
3
H
N
Melatonin
O
CH
3
TARGET POINTS
Pineal gland is also known as epiphysis cerebri as it is a part of brain. It is ectodermal in
origin.
It is called third eye in frog.
If pineal body is removed from rats, these will attain premature adolescence.
Children blind from birth attain puberty earlier than normal.
121
5.3 THYROID GLAND
The thyroid gland possesses two lobes that are
connected by the isthmus. It is located in the neck,
just below the larynx with the isthmus in front of
and lobes lateral to the trachea. It has a dark red
colour due to its extensive vasculature. When the
thyroid increases in size due to dysfunction, it can
be felt under the skin of the neck. The main
function of the thyroid gland is the synthesis and
storage of thyroid hormones that are involved in
maintaining metabolic homeostasis.
The thyroid gland is made up of many spherical
thyroid follicles, which are lined with simple cuboidal epithelium. These follicles contain a viscous
fluid called colloid that stores the glycoprotein thyroglobulin, the precursor to the two thyroid
hormones. Thyroglobulin is not normally released into circulation unless the thyroid gland is damaged
due to disease or injury. Other endocrine cells, called parafollicular cells, are located between adjacent
follicles and produce a different hormone, calcitonin, that is involved in blood calcium homeostasis.
Thyroid follicle
(containing thyroglobulin)
Follicular cells
Parafollicular cell
Capsule of
connective
tissue
Capillary
Colloid is a
glycoprotein
Follicular cells secrete
thyroid hormone
C cells secrete
calcitonin
Thyroid
follicle
Thyroid follicles
Thyroglobulin is produced and secreted by follicle cells into the lumen of follicles as a colloid. There
it undergoes post translational modification to produce functioning thyroid hormones. Iodide molecules
are added to the thyroglobulin precursor to produce the hormones thyroxin and triiodothyronine.
Thyroxine is also known as T
4
because it contains four atoms of iodine, and triiodothyronine is also
known as T
3
because it contains three atoms of iodine.
Iodide ions are actively transported into the follicular lumen from the capillaried by follicle cells.
Follicle cells are stimulated to release stored T
3
and T
4
from the lumen into the blood capillaries by
thyroid stimulating hormone (TSH), which is produced by the anterior pituitary. Follicle cells also
begin synthesizing more T
3
and T
4
in response to TSH stimulation.
T
4
contains two phenyl rings linked up by an ether bridge. Follicular cells take up KI (iodine trapping)
and oxidize it into I
2
. Oxidation is promoted by the enzyme peroxidase.
Superior thyroid artery
Larynx
Thyroid gland
Isthmus
Common carotid artery
Inferior thyroid artery
Trachea
Thyroid gland
5.3 THYROID GLAND
The thyroid gland possesses two lobes that are
connected by the isthmus. It is located in the neck,
just below the larynx with the isthmus in front of
and lobes lateral to the trachea. It has a dark red
colour due to its extensive vasculature. When the
thyroid increases in size due to dysfunction, it can
be felt under the skin of the neck. The main
function of the thyroid gland is the synthesis and
storage of thyroid hormones that are involved in
maintaining metabolic homeostasis.
The thyroid gland is made up of many spherical
thyroid follicles, which are lined with simple cuboidal epithelium. These follicles contain a viscous
fluid called colloid that stores the glycoprotein thyroglobulin, the precursor to the two thyroid
hormones. Thyroglobulin is not normally released into circulation unless the thyroid gland is damaged
due to disease or injury. Other endocrine cells, called parafollicular cells, are located between adjacent
follicles and produce a different hormone, calcitonin, that is involved in blood calcium homeostasis.
Thyroid follicle
(containing thyroglobulin)
Follicular cells
Parafollicular cell
Capsule of
connective
tissue
Capillary
Colloid is a
glycoprotein
Follicular cells secrete
thyroid hormone
C cells secrete
calcitonin
Thyroid
follicle
Thyroid follicles
Thyroglobulin is produced and secreted by follicle cells into the lumen of follicles as a colloid. There
it undergoes post translational modification to produce functioning thyroid hormones. Iodide molecules
are added to the thyroglobulin precursor to produce the hormones thyroxin and triiodothyronine.
Thyroxine is also known as T
4
because it contains four atoms of iodine, and triiodothyronine is also
known as T
3
because it contains three atoms of iodine.
Iodide ions are actively transported into the follicular lumen from the capillaried by follicle cells.
Follicle cells are stimulated to release stored T
3
and T
4
from the lumen into the blood capillaries by
thyroid stimulating hormone (TSH), which is produced by the anterior pituitary. Follicle cells also
begin synthesizing more T
3
and T
4
in response to TSH stimulation.
T
4
contains two phenyl rings linked up by an ether bridge. Follicular cells take up KI (iodine trapping)
and oxidize it into I
2
. Oxidation is promoted by the enzyme peroxidase.
Superior thyroid artery
Larynx
Thyroid gland
Isthmus
Common carotid artery
Inferior thyroid artery
Trachea
Thyroid gland
122
Tyrosine + I
2
MIT and DIT
MIT + DIT T
3
DIT + DIT T
4
T
1
= Monoiodotyrosine; T
2
= Diiodotyrosine; T
3
= Triiodothyronine (20%); T
4
= Tetraiodothyronine (80%)
Secretion of T
4
is comparatively more than T
3
, but T
3
is four times more effective than T
4
. T
4
changes
into T
3
on reaching tissues. Each thyroglobulin molecule contains an average of T
3
molecules for
every 14 molecules of T
4
(1:14 = T
3
:T
4
).
T
3
T
4
Secretion T
3
T
4Proteases
Colloid
droplet
Pinocytosis
T
G
MIT
DIT
T
T
3
4
Iodination
and
coupling
T
G
+
H
2O
2
Peroxidase
Peroxidase
Thyroglobulin
precursor ( )T
G
GolgiER
MIT, DIT
I
2
Tyrosine
Deiodination
I
–
I
–
Thyroid cellular mechanisms for iodine transport, T
4
and T
3
formation and their release into
blood
Thyroid gland requires 120 g iodine every day for thyroxine production. Normal recommended
minimum intake is 200 g/day, if iodine intake <50 g/day, thyroid disorder develops. Iodine deficiency
causes thyroid to absorb more and more iodine from blood and thus, increases its size, it is called
simple goitre.
Goitre is found more abundantly in individuals living on mountain slopes, because iodine there flows
along with water. When many show the symptoms of this disease, it is called endemic goitre.
Those consuming sea foods, never show the symptoms of goitre.
5.3.1 Effect of thyroid hormone on growth and metabolism
A. Growth
Thyroid hormone has both general and specific effects on growth. For instance, thyroid hormone is
essential for the metamorphic change of the tadpole into the frog.
Tyrosine + I
2
MIT and DIT
MIT + DIT T
3
DIT + DIT T
4
T
1
= Monoiodotyrosine; T
2
= Diiodotyrosine; T
3
= Triiodothyronine (20%); T
4
= Tetraiodothyronine (80%)
Secretion of T
4
is comparatively more than T
3
, but T
3
is four times more effective than T
4
. T
4
changes
into T
3
on reaching tissues. Each thyroglobulin molecule contains an average of T
3
molecules for
every 14 molecules of T
4
(1:14 = T
3
:T
4
).
T
3
T
4
Secretion T
3
T
4Proteases
Colloid
droplet
Pinocytosis
T
G
MIT
DIT
T
T
3
4
Iodination
and
coupling
T
G
+
H
2O
2
Peroxidase
Peroxidase
Thyroglobulin
precursor ( )T
G
GolgiER
MIT, DIT
I
2
Tyrosine
Deiodination
I
–
I
–
Thyroid cellular mechanisms for iodine transport, T
4
and T
3
formation and their release into
blood
Thyroid gland requires 120 g iodine every day for thyroxine production. Normal recommended
minimum intake is 200 g/day, if iodine intake <50 g/day, thyroid disorder develops. Iodine deficiency
causes thyroid to absorb more and more iodine from blood and thus, increases its size, it is called
simple goitre.
Goitre is found more abundantly in individuals living on mountain slopes, because iodine there flows
along with water. When many show the symptoms of this disease, it is called endemic goitre.
Those consuming sea foods, never show the symptoms of goitre.
5.3.1 Effect of thyroid hormone on growth and metabolism
A. Growth
Thyroid hormone has both general and specific effects on growth. For instance, thyroid hormone is
essential for the metamorphic change of the tadpole into the frog.
123
In humans, the effect of thyroid hormone on growth is manifest mainly in growing children. In those
who are hypothyroid, the rate of growth is greatly reatarded. In those who are hyperthyroid, excessive
skeletal growth often occurs, causing the child to become considerably taller at an earlier age.
However, the bones also mature moe rapidly and he epiphyses close at an early age, so that the
duration of growth and the eventual height of the adult may actually be shortened.
An important effect of thyroid hormone is to promote growth and development of the brain during
fetal life and for the first few years of postnatal life. If the fetus does not secrete sufficient quantities
of thyroid hormone, growth and maturation of the brain both before birth and afterward are greatly
retarded, and the brain remains smaller than normal. Without specific thyroid therapy within days or
weeks after birth, the child without a thyroid gland will remain mentally deficient throughout life.
B. Metabolism
Thyroid hormones increase cellular metabolic activity. The basal metabolic rate increases to 60-
100% above normal when large quantities of hormones are secreted. The rate of utilization of foods
for energy is greatly accelerated.
Thyroid hormones increase (i) the number and activity of mitochondria and (ii) increase active
transport of ions through cell membranes (Na
+
-K
+
-ATPase).
Carbohydrate metabolism: Blood sugar increases, acts as a diabetogenic hormone.
Fat metabolism: Enhances enzyme activity, both synthesis and predominant catabolism of
cholesterol.
Protein metabolism: Although the rate of protein synthesis is increased, at the same time the rate
of protein catabolism is also increased.
C. On body organs
Heart: Thyroxine
heartbeat(Tachycardia)cardiac output
T
4
maintains the contraction of myocardium and regulates heartbeat as it acts directly on SA-node.
CNS: Optimum conc. of T
4
is required for the development of nerve fibres and their myelination.
GIT: T
4
increases its motility causing diarrhoea. Appetite also increases.
Blood: T
4
stimulates RBC formation.
5.3.2 Regulation of thyroid hormone secretion
TSH (from the anterior pituitary gland) increases the secretion of thyroxin and triiodothyronine by
the thyroid gland. Its specific effects on the thyroid gland are as follows:
1. Increased proteolysis of the thyroglobulin that has already been stored in the follicles, with
resultant release of the thyroid hormones into the circulating blood and diminishment of the
follicular substance itself.
2. Increased activity of the iodide pump, which increases the rate of “iodide trapping” in the
glandular cells, sometimes increasing the ratio of intracellular to extracellular iodide
concentration in the glandular substance to as much as eight times normal.
In humans, the effect of thyroid hormone on growth is manifest mainly in growing children. In those
who are hypothyroid, the rate of growth is greatly reatarded. In those who are hyperthyroid, excessive
skeletal growth often occurs, causing the child to become considerably taller at an earlier age.
However, the bones also mature moe rapidly and he epiphyses close at an early age, so that the
duration of growth and the eventual height of the adult may actually be shortened.
An important effect of thyroid hormone is to promote growth and development of the brain during
fetal life and for the first few years of postnatal life. If the fetus does not secrete sufficient quantities
of thyroid hormone, growth and maturation of the brain both before birth and afterward are greatly
retarded, and the brain remains smaller than normal. Without specific thyroid therapy within days or
weeks after birth, the child without a thyroid gland will remain mentally deficient throughout life.
B. Metabolism
Thyroid hormones increase cellular metabolic activity. The basal metabolic rate increases to 60-
100% above normal when large quantities of hormones are secreted. The rate of utilization of foods
for energy is greatly accelerated.
Thyroid hormones increase (i) the number and activity of mitochondria and (ii) increase active
transport of ions through cell membranes (Na
+
-K
+
-ATPase).
Carbohydrate metabolism: Blood sugar increases, acts as a diabetogenic hormone.
Fat metabolism: Enhances enzyme activity, both synthesis and predominant catabolism of
cholesterol.
Protein metabolism: Although the rate of protein synthesis is increased, at the same time the rate
of protein catabolism is also increased.
C. On body organs
Heart: Thyroxine
heartbeat(Tachycardia)cardiac output
T
4
maintains the contraction of myocardium and regulates heartbeat as it acts directly on SA-node.
CNS: Optimum conc. of T
4
is required for the development of nerve fibres and their myelination.
GIT: T
4
increases its motility causing diarrhoea. Appetite also increases.
Blood: T
4
stimulates RBC formation.
5.3.2 Regulation of thyroid hormone secretion
TSH (from the anterior pituitary gland) increases the secretion of thyroxin and triiodothyronine by
the thyroid gland. Its specific effects on the thyroid gland are as follows:
1. Increased proteolysis of the thyroglobulin that has already been stored in the follicles, with
resultant release of the thyroid hormones into the circulating blood and diminishment of the
follicular substance itself.
2. Increased activity of the iodide pump, which increases the rate of “iodide trapping” in the
glandular cells, sometimes increasing the ratio of intracellular to extracellular iodide
concentration in the glandular substance to as much as eight times normal.
124
3. Increased iodination of tyrosine to form the thyroid hormones.
4. Increased size and increased secretory activity of the thyroid cells.
5. Increased number of thyroid cells plus a change from cuboidal to columnar cells and much
infolding of the thyroid epithelium into the follicles.
Hypothalamus
(paraventricularnuclei)
TRH
(+)
TSH
(+)
Liver conjugation/
excretion
Kidney
excretion
Pituitary
Thyroid
(Follicle)
Circulating T and T
free (active) or
bound to TBG, albumin
3 4
Peripheral conversion of
T to active T
4 3
Target tissue
(via THR /THR
nuclear receptors)
(+)
(-)
(-)
5.3.3. Disorders A. Hyposecretion/Hypothyroidism
May be a genetic disorder or deficiency of iodine.
In children, hypothyroidism causes Cretinism, these children are called cretin and may show
symptoms like thick lips, protruding tongue, pot belly, ill developed sex organs and retarded
physical and mental growth. The children remain dwarf, become ugly and sterile. Their BMR,
rate of heartbeat and body temperature decreases.
May cause abnormal skin, deaf - mutism.
In women, hypothyroidism may cause irregular menstrual cycle.
Myxoedema (Gull’s disease): In adults symptoms are falling of hair, loose and swollen skin,
deposition of adipose fat and mucous beneath the skin. Body becomes obese; BMR and
blood pressure are reduced. Patient becomes sensitive to cold and shows loss of sexual
power. Mental slowing, bradycardia, weight gain occurs.
3. Increased iodination of tyrosine to form the thyroid hormones.
4. Increased size and increased secretory activity of the thyroid cells.
5. Increased number of thyroid cells plus a change from cuboidal to columnar cells and much
infolding of the thyroid epithelium into the follicles.
Hypothalamus
(paraventricularnuclei)
TRH
(+)
TSH
(+)
Liver conjugation/
excretion
Kidney
excretion
Pituitary
Thyroid
(Follicle)
Circulating T and T
free (active) or
bound to TBG, albumin
3 4
Peripheral conversion of
T to active T
4 3
Target tissue
(via THR /THR
nuclear receptors)
(+)
(-)
(-)
5.3.3. Disorders A. Hyposecretion/Hypothyroidism
May be a genetic disorder or deficiency of iodine.
In children, hypothyroidism causes Cretinism, these children are called cretin and may show
symptoms like thick lips, protruding tongue, pot belly, ill developed sex organs and retarded
physical and mental growth. The children remain dwarf, become ugly and sterile. Their BMR,
rate of heartbeat and body temperature decreases.
May cause abnormal skin, deaf - mutism.
In women, hypothyroidism may cause irregular menstrual cycle.
Myxoedema (Gull’s disease): In adults symptoms are falling of hair, loose and swollen skin,
deposition of adipose fat and mucous beneath the skin. Body becomes obese; BMR and
blood pressure are reduced. Patient becomes sensitive to cold and shows loss of sexual
power. Mental slowing, bradycardia, weight gain occurs.
125
Simple goitre/Endemic goitre: Occurs due to iodine deficiency in food, also known as colloid
goitre. Thyroid gland and neck swells up, looks like a collar. It is cured by extra intake of
iodine in food or intake of sea food. It is not a genetic disorder.
Hashimoto’s disease: There is acute deficiency of T
4
. Medicines given for the treatment or
even T
4
itself acts as poison or antigen. In its reaction, body produces antibodies that destroy
the thyroid gland itself. It is known also as suicide of thyroid or autoimmune thyroiditis.
B. Hypersecretion/Hyperthyroidism
Microbial infections or genetic disorders enlarge the gland and T
4
is secreted in excess.
BMR, heartbeat rate, bp, and glucose absorption in intestine and oxygen consumption increase.
Too much energy is produced in mitochondria, that it is not stored in the form of ATP but
released as heat in the body. Thus in place of growth, unnecessary irritation, exhaustion are
observed. Due to excess heat/calorie/energy formation, patient feels extremely hot.
Exophthalmic goiter/Grave’s disease/Basedow’s disease/Thyrotoxicosis: Deposition of
mucous beneath the eyeball takes place, eyes look enlarged or protruding outside eye sockets.
The whole gland shows enlargement in the neck region.
Plummer’s disease: Thyroid gland does not show growth but there become small tumors all
over it just like buds. It is also called toxic adenoma.
Plummer’s diseaseGrave`s disease
Node
TARGET POINTS
Thyroid, endodermal in origin, is the largest endocrine gland in the body. It is bilobed in birds
and mammals, but single lobed in reptiles.
Isthmus is a non-glandular band, formed of connective tissue.
Endostyle of lower vertebrates like Herdmania, Amphioxus is homologous of thyroid gland.
In humans, the gland weighs about 25-35 g approximately, somewhat larger in women as
compared to men.
Thyroid is the only endocrine gland in the body which stores its hormone in its inactive state.
Organification: Binding of iodine with thyroglobulin molecule is called organification of
thyroglobulin.
Thyroglobulins are stored in the follicles in an amount sufficient to supply body with its normal
requirements of thyroid hormone for 3 months.
Simple goitre/Endemic goitre: Occurs due to iodine deficiency in food, also known as colloid
goitre. Thyroid gland and neck swells up, looks like a collar. It is cured by extra intake of
iodine in food or intake of sea food. It is not a genetic disorder.
Hashimoto’s disease: There is acute deficiency of T
4
. Medicines given for the treatment or
even T
4
itself acts as poison or antigen. In its reaction, body produces antibodies that destroy
the thyroid gland itself. It is known also as suicide of thyroid or autoimmune thyroiditis.
B. Hypersecretion/Hyperthyroidism
Microbial infections or genetic disorders enlarge the gland and T
4
is secreted in excess.
BMR, heartbeat rate, bp, and glucose absorption in intestine and oxygen consumption increase.
Too much energy is produced in mitochondria, that it is not stored in the form of ATP but
released as heat in the body. Thus in place of growth, unnecessary irritation, exhaustion are
observed. Due to excess heat/calorie/energy formation, patient feels extremely hot.
Exophthalmic goiter/Grave’s disease/Basedow’s disease/Thyrotoxicosis: Deposition of
mucous beneath the eyeball takes place, eyes look enlarged or protruding outside eye sockets.
The whole gland shows enlargement in the neck region.
Plummer’s disease: Thyroid gland does not show growth but there become small tumors all
over it just like buds. It is also called toxic adenoma.
Plummer’s diseaseGrave`s disease
Node
TARGET POINTS
Thyroid, endodermal in origin, is the largest endocrine gland in the body. It is bilobed in birds
and mammals, but single lobed in reptiles.
Isthmus is a non-glandular band, formed of connective tissue.
Endostyle of lower vertebrates like Herdmania, Amphioxus is homologous of thyroid gland.
In humans, the gland weighs about 25-35 g approximately, somewhat larger in women as
compared to men.
Thyroid is the only endocrine gland in the body which stores its hormone in its inactive state.
Organification: Binding of iodine with thyroglobulin molecule is called organification of
thyroglobulin.
Thyroglobulins are stored in the follicles in an amount sufficient to supply body with its normal
requirements of thyroid hormone for 3 months.
126
E.C. Kendal first crystallized T
4
hormone. Harrington and Barger studied its molecular structure.
Paedogenesis: Some amphibian larvae eg. Ambystoma and Necturus (water dog) do not
undergo metamorphosis to be an adult, and these larval stages start reproducing without gaining
adulthood.
Calorigenesis: Over production of heat. Thyroid hormone enhances the oxidative metabolism
of body cells, energy production is increased in the form of calories, thus, this hormone is also
called calorigenic hormone.
Parafollicular/C cells: They are the remains of ultimobranchial bodies made up of 5
th
branchial
pouches of embryo, i.e. endodermal in origin. Thyrocalcitonin reduces the destruction of bones
and increases the rate of excretion of Ca
++
in urine, thus reduces Ca
++
level in ECF. It enhances
Ca
++
deposition in bones, making them strong and solid. This hormone acts antagonistic to
Collip’s hormone or parathormone.
5.4 PARATHYROID GLAND
The four parathyroid glands are each the size of a grain
of rice and are usually located on the posterior surface
of the thyroid gland. The exact location and number of
parathyroid glands can vary from person to person. It
weighs about 140 mg and is of dimension 6 × 3 × 2
mm. These glands are made by epithelium of third and
fourth branchial pouches or pharyngeal pouches slits
of embryo i.e. endodermal in origin.
Each parathyroid gland is covered by connective tissue
and contains many secretory cells called chief cells,
which synthesize and secrete parathyroid hormone
(PTH).
PTH is synthesized as a pro pepide that is cleaved
into an active hormone, which is vital in maintaining
blood calcium levels. Calcium is required for nerve
impulse transmission, for muscle contractions and for
many cellular processes- including signal transduction.
Therefore, plasma calcium concentrations must be
maintained within a narrow normal range of 9 – 10 mg/
dl. PTH functions by increasing blood calcium
concentrations when calcium ion levels fall below normal.
Calcium ions bind to specific receptors on the chief cell
and inhibit release of PTH; when the plasma calcium
level falls. PTH secretion is stimulated. PTH stimulates
Red blood cell
Oxyphil cell
Chief cell
Parathyroid gland
(located on posterior
side of the thyroid
gland)
Thyroid
gland
Calcium complexed to
anions 9% (0.2 mmol/L
Ionized calcium
50%
(1.2 mmol/L)
Protein-bound
calcium
41%
(1.0 mmol/L
E.C. Kendal first crystallized T
4
hormone. Harrington and Barger studied its molecular structure.
Paedogenesis: Some amphibian larvae eg. Ambystoma and Necturus (water dog) do not
undergo metamorphosis to be an adult, and these larval stages start reproducing without gaining
adulthood.
Calorigenesis: Over production of heat. Thyroid hormone enhances the oxidative metabolism
of body cells, energy production is increased in the form of calories, thus, this hormone is also
called calorigenic hormone.
Parafollicular/C cells: They are the remains of ultimobranchial bodies made up of 5
th
branchial
pouches of embryo, i.e. endodermal in origin. Thyrocalcitonin reduces the destruction of bones
and increases the rate of excretion of Ca
++
in urine, thus reduces Ca
++
level in ECF. It enhances
Ca
++
deposition in bones, making them strong and solid. This hormone acts antagonistic to
Collip’s hormone or parathormone.
5.4 PARATHYROID GLAND
The four parathyroid glands are each the size of a grain
of rice and are usually located on the posterior surface
of the thyroid gland. The exact location and number of
parathyroid glands can vary from person to person. It
weighs about 140 mg and is of dimension 6 × 3 × 2
mm. These glands are made by epithelium of third and
fourth branchial pouches or pharyngeal pouches slits
of embryo i.e. endodermal in origin.
Each parathyroid gland is covered by connective tissue
and contains many secretory cells called chief cells,
which synthesize and secrete parathyroid hormone
(PTH).
PTH is synthesized as a pro pepide that is cleaved
into an active hormone, which is vital in maintaining
blood calcium levels. Calcium is required for nerve
impulse transmission, for muscle contractions and for
many cellular processes- including signal transduction.
Therefore, plasma calcium concentrations must be
maintained within a narrow normal range of 9 – 10 mg/
dl. PTH functions by increasing blood calcium
concentrations when calcium ion levels fall below normal.
Calcium ions bind to specific receptors on the chief cell
and inhibit release of PTH; when the plasma calcium
level falls. PTH secretion is stimulated. PTH stimulates
Red blood cell
Oxyphil cell
Chief cell
Parathyroid gland
(located on posterior
side of the thyroid
gland)
Thyroid
gland
Calcium complexed to
anions 9% (0.2 mmol/L
Ionized calcium
50%
(1.2 mmol/L)
Protein-bound
calcium
41%
(1.0 mmol/L
127
reabsorption of calcium from filtrate during urine formation, increased absorption in the intestines
from digested products and increased activity of osteoclasts to release calcium (and phosphate)
from bone matrix into the plasma.
PTH also accelerates elimination of phosphate in urine (phosphaturic action). Thus, calcium level
tends to rise in ECF and phosphate level decreases. This calcium is then utilized by osteoblasts in
bone formation under the influence of vitamin D3. PTH stimulates osteoclasts to feed upon bones,
and remove the unnecessary parts by melting, thus PTH change asymmetrical bone into symmetrical
bone. The remolding of bone is done by these cells lifelong. As a result of this, amount of Ca
++
remains constant in blood in normal conditions.
Hyposecretion of PTH decreases Ca
++
level in ECF causing hypocalcemia. Muscles and nerves
get unnecessarily irritated and start convulsion and cramping. Tetany is when the voluntary muscles
remain contracted for a long time. If this happens in intercostal muscles and diaphragm, then animal
dies due to Asphyxia.
A parathyroid adenoma is a benign tumor of the parathyroid gland that can cause an overproduction
of PTH leading to hyperparathyroidism. Hyperparathyroidism results in hypercalcemia, which can
lead to kidney stones. Additionally, increased rate of bone resoprtion due to higher osteoclast activity
due to this condition may also lead to osteoporosis. Usually only one of the four parathyroid glands
is affected and can be surgically removed without any adverse effects. However, removal of all the
parathyroid glands will cause an imbalance in blood calcium levels resulting in death.
TARGET POINTS
Raynard discovered the parathyroid gland while its detailed description was given by Sandrom.
PTH is also known as Collip’s hormone as it was obtained by Collip in its pure form.
Maintenance of proper calcium level under homeostasis is a combined function of parathormone,
thyrocalcitonin and vitamin D3 (cholecalciferol). Each 100 ml blood contains 12 mg of Ca
++
,
about 1 kg of calcium is found in an adult man.
5.5 THYMUS GLAND
The thymus is an organ that is found behind the sternum and is most prominent in infants, becoming
smaller in size through adulthood, replaced by adipose tissue that continues to produce angiogenic
factors.
Thymus is bilobed and originated by third branchial pouch of embryo, i.e. endodermal in origin. Its
structure is just like a lymph gland. It is covered by connective tissue coat capsule and internally
both lobes redivide into small lobules. Each lobule has a dense, darkly staining peripheral cortex
and a looser lightly staining central medulla. Cortex consists of densely packed lymphocytes while
medulla consists of reticular epithelial cells, a few lymphocytes and the Corpuscles of Hassalls
(thymic corpuscles) which act as phagocytes.
reabsorption of calcium from filtrate during urine formation, increased absorption in the intestines
from digested products and increased activity of osteoclasts to release calcium (and phosphate)
from bone matrix into the plasma.
PTH also accelerates elimination of phosphate in urine (phosphaturic action). Thus, calcium level
tends to rise in ECF and phosphate level decreases. This calcium is then utilized by osteoblasts in
bone formation under the influence of vitamin D3. PTH stimulates osteoclasts to feed upon bones,
and remove the unnecessary parts by melting, thus PTH change asymmetrical bone into symmetrical
bone. The remolding of bone is done by these cells lifelong. As a result of this, amount of Ca
++
remains constant in blood in normal conditions.
Hyposecretion of PTH decreases Ca
++
level in ECF causing hypocalcemia. Muscles and nerves
get unnecessarily irritated and start convulsion and cramping. Tetany is when the voluntary muscles
remain contracted for a long time. If this happens in intercostal muscles and diaphragm, then animal
dies due to Asphyxia.
A parathyroid adenoma is a benign tumor of the parathyroid gland that can cause an overproduction
of PTH leading to hyperparathyroidism. Hyperparathyroidism results in hypercalcemia, which can
lead to kidney stones. Additionally, increased rate of bone resoprtion due to higher osteoclast activity
due to this condition may also lead to osteoporosis. Usually only one of the four parathyroid glands
is affected and can be surgically removed without any adverse effects. However, removal of all the
parathyroid glands will cause an imbalance in blood calcium levels resulting in death.
TARGET POINTS
Raynard discovered the parathyroid gland while its detailed description was given by Sandrom.
PTH is also known as Collip’s hormone as it was obtained by Collip in its pure form.
Maintenance of proper calcium level under homeostasis is a combined function of parathormone,
thyrocalcitonin and vitamin D3 (cholecalciferol). Each 100 ml blood contains 12 mg of Ca
++
,
about 1 kg of calcium is found in an adult man.
5.5 THYMUS GLAND
The thymus is an organ that is found behind the sternum and is most prominent in infants, becoming
smaller in size through adulthood, replaced by adipose tissue that continues to produce angiogenic
factors.
Thymus is bilobed and originated by third branchial pouch of embryo, i.e. endodermal in origin. Its
structure is just like a lymph gland. It is covered by connective tissue coat capsule and internally
both lobes redivide into small lobules. Each lobule has a dense, darkly staining peripheral cortex
and a looser lightly staining central medulla. Cortex consists of densely packed lymphocytes while
medulla consists of reticular epithelial cells, a few lymphocytes and the Corpuscles of Hassalls
(thymic corpuscles) which act as phagocytes.
128
Newbord 10 Years old25 Years old50 Years old70 Years old
Thymus organ
morphology
Histological pattern
of a thymic lobule
Vessels Perivascular space Adipose tissue in perivascular space
The thymus is part of the immune system, with a role in maturation and immunocompetence of T –
lymphocytes. The thymus also produces a group of hormones called thymosins, because they were
first discovered from the thymus, but now are understood to be produced by many different tissues
in the body. They appear to have an anti inflammatory effect and stimulate tissue repair. Thymosin
is also involved in neuroplasticity, and they may have clinical implications in the treatment of
cardiovascular, infectious and autoimmune diseases as well as cancer.
Thymosin stimulates the maturation of lymphocytes to destroy antigens produced by bacteria or
pathogens. As cell mediated immunity is provided thus, thymus is also called the ‘throne of immunity’
or the ‘training school of T-lymphocytes’. Thymosin promotes the production of antibody and provides
humoral immunity.
Thymosin helps in development of sex glands but inhibits sexual maturity in early young age. Secretion
of thymin decreases the neuromuscular transmission; hypersecretion may cause myasthenia gravis,
provides antibody against the receptors and block the NM junction.
TARGET POINTS
Disappearance of thymus gland in middle age is the primary cause of ageing.
5.6 ADRENAL GLANDS
The adrenal glands help regulate the body’s response to stress, controlling blood pressure, and
maintaining the body’s water, sodium, and potassium levels. The adrenal glands are associated
with the pair of kidneys which are retroperitoneal and lateral to the spinal column; one gland is
located on the superior surface of each kidney (hence they are also known as suprarenal glands).
The adrenal glands consist of an outer adrenal cortex (cortex means outer layer) and an inner
adrenal medulla (medulla means middle). Functionally and anatomically the adrenal gland is really
two glands packaged together. The cells of the cortex are endocine and those of the medulla are
Newbord 10 Years old25 Years old50 Years old70 Years old
Thymus organ
morphology
Histological pattern
of a thymic lobule
Vessels Perivascular space Adipose tissue in perivascular space
The thymus is part of the immune system, with a role in maturation and immunocompetence of T –
lymphocytes. The thymus also produces a group of hormones called thymosins, because they were
first discovered from the thymus, but now are understood to be produced by many different tissues
in the body. They appear to have an anti inflammatory effect and stimulate tissue repair. Thymosin
is also involved in neuroplasticity, and they may have clinical implications in the treatment of
cardiovascular, infectious and autoimmune diseases as well as cancer.
Thymosin stimulates the maturation of lymphocytes to destroy antigens produced by bacteria or
pathogens. As cell mediated immunity is provided thus, thymus is also called the ‘throne of immunity’
or the ‘training school of T-lymphocytes’. Thymosin promotes the production of antibody and provides
humoral immunity.
Thymosin helps in development of sex glands but inhibits sexual maturity in early young age. Secretion
of thymin decreases the neuromuscular transmission; hypersecretion may cause myasthenia gravis,
provides antibody against the receptors and block the NM junction.
TARGET POINTS
Disappearance of thymus gland in middle age is the primary cause of ageing.
5.6 ADRENAL GLANDS
The adrenal glands help regulate the body’s response to stress, controlling blood pressure, and
maintaining the body’s water, sodium, and potassium levels. The adrenal glands are associated
with the pair of kidneys which are retroperitoneal and lateral to the spinal column; one gland is
located on the superior surface of each kidney (hence they are also known as suprarenal glands).
The adrenal glands consist of an outer adrenal cortex (cortex means outer layer) and an inner
adrenal medulla (medulla means middle). Functionally and anatomically the adrenal gland is really
two glands packaged together. The cells of the cortex are endocine and those of the medulla are
129
neurosecretory. The cells look very different and embryologically they come from different tissues.
These regions secrte different hormones: the adrenal cortex produces steroid hormones, and the
adrenal medulla produces catecholamines hormones.
Transverse section Microscopic section
Adrenal medulla
Adrenal cortex
Capsule
Mineralocorticoids
Glucocorticoids
Adrenal androgens
Catecholamines
Epinephrine
Splanchnic nerves
Medullary veins
Chromaffin cells
Medulla
Cortex
Reticularis
Fasciculata
Glomerulosa
Capsule
5.6.1 Adrenal cortex
The adrenal cortex is the outer layer of the adrenal gland and is made up of layers of epithelial cells
and associated capillary networks. These layers form three distinct regions that secrete different
steroid hormones: the outer zona glomerulosa produces mineralocorticoids (influence salt and water
balance), the middle zona fasciculata produces glucocorticoids (impact metabolism and
inflammation), and the inner zona reticularis produces androgens (regulate catabolism and sexual
characteristics).
Zona fasciculate consists of polyangular cells arranged in layers. Cells of zona reticularis are spread
in the form of a network and arranged in layers. About 40-50 hormones are synthesized in adrenal
cortex, out of which only 7-8 hormones are active.
A. Mineralocorticoid
The main mineralocorticoid is aldosterone, which reguates the concentration of ions in urine, sweat
and saliva. Aldosterone release from the adrenal cortex can be triggered by a number of things
including decrease in blood concentration of sodium ions, blood volume, or blood pressure, or an
increase in blood potassium levels.
Aldosterone affects DCTs and early cortical tubule of kidneys. It basically activates the Na
+
–K
+
pump and helps in reabsorption of Na
+
and Cl
-
and controls the K
+
excretion, thus also known as
salt retaining hormone. Excessive increase in Na
+
in ECF causes hypernatremia. There is
tremendous loss (by urination) of Na
+
, Cl
-
and HCO
3
-
under aldosterone hyposecretion.
Deoxycorticosterone, an active Na
+
retaining mineralocorticoid, acts as a precursor to aldosterone.
B. Glucocorticoid
The three main glucocorticoids are cortisol, corticosterone, and cortisone. The glucocorticoids
simulate the synthesis of glucosse from non glycogen sources, and they promote the release of
neurosecretory. The cells look very different and embryologically they come from different tissues.
These regions secrte different hormones: the adrenal cortex produces steroid hormones, and the
adrenal medulla produces catecholamines hormones.
Transverse section Microscopic section
Adrenal medulla
Adrenal cortex
Capsule
Mineralocorticoids
Glucocorticoids
Adrenal androgens
Catecholamines
Epinephrine
Splanchnic nerves
Medullary veins
Chromaffin cells
Medulla
Cortex
Reticularis
Fasciculata
Glomerulosa
Capsule
5.6.1 Adrenal cortex
The adrenal cortex is the outer layer of the adrenal gland and is made up of layers of epithelial cells
and associated capillary networks. These layers form three distinct regions that secrete different
steroid hormones: the outer zona glomerulosa produces mineralocorticoids (influence salt and water
balance), the middle zona fasciculata produces glucocorticoids (impact metabolism and
inflammation), and the inner zona reticularis produces androgens (regulate catabolism and sexual
characteristics).
Zona fasciculate consists of polyangular cells arranged in layers. Cells of zona reticularis are spread
in the form of a network and arranged in layers. About 40-50 hormones are synthesized in adrenal
cortex, out of which only 7-8 hormones are active.
A. Mineralocorticoid
The main mineralocorticoid is aldosterone, which reguates the concentration of ions in urine, sweat
and saliva. Aldosterone release from the adrenal cortex can be triggered by a number of things
including decrease in blood concentration of sodium ions, blood volume, or blood pressure, or an
increase in blood potassium levels.
Aldosterone affects DCTs and early cortical tubule of kidneys. It basically activates the Na
+
–K
+
pump and helps in reabsorption of Na
+
and Cl
-
and controls the K
+
excretion, thus also known as
salt retaining hormone. Excessive increase in Na
+
in ECF causes hypernatremia. There is
tremendous loss (by urination) of Na
+
, Cl
-
and HCO
3
-
under aldosterone hyposecretion.
Deoxycorticosterone, an active Na
+
retaining mineralocorticoid, acts as a precursor to aldosterone.
B. Glucocorticoid
The three main glucocorticoids are cortisol, corticosterone, and cortisone. The glucocorticoids
simulate the synthesis of glucosse from non glycogen sources, and they promote the release of
130
fatty acids from adipose tissue. These hormones increase blood glucose levels to maintain levels
within a normal range between meals. They are secreted in response to ACTH, and levels are
regulated by negative feedback.
Cortisol (lifesaving hormone): Secreted by zona fasciculata, also known as hydrocorticosterone.
Cortisol has a small amount of mineralocorticoid activity.
Cortisol (i) increases sugar in blood causing hyperglycemia, (ii) causes protein lysis in some organs
like lymphoid tissues (thymus, lymph node etc), muscles, bones, skin etc. Deamination & urea
formation stimulate or inhibit protein synthesis, (iii) facilitates lipolysis and promotes deposition of
fat, in unusual sites of the body, (iv) inhibit nucleic acid synthesis in all other tissues except liver
where RNA synthesis increases, (v) prevent WBC actions and collagen fibres in tissues (anti-
inflammatory hormone) and thus, used in diseases like edema, arthritis/rheumatism, (vi) checks
immune reactions by antibodies (immuno-suppressive) and (vii) used in transplantation of organs.
C. Androgens
Androgens are a class of hormones and that affect sexual characteristics. Testosterone is associated
with male sexual characteristics, while progesterone and estrogen are associated with female
reproductive function: androstenedione is an intermediate molecule in the synthetic pathways of
these and many of the steroid hormones.
These hormones stimulate the muscles, external genitalia and sexual behaviour. Male hormone
secreted is mainly dehydroepiandrosterone [DHEA].
In situations where the gonads are not functioning the progesterone made in the adrenal glands
does influence sexual characteristics. One of the reasons why post menopausal women develop
more male characteristics is that the progesterone their adrenal makes gets converted to testosterone.
5.6.2 Adrenal medulla
The adrenal medulla is the inner layer of the adrenal glands and contains chromaffin cells, which
are large, irregularly shaped cells that are closely associated with blood vessels. These cells are
innervated by autonomic (involuntary) nerve fibers from the central nervous system, which allows
for quick hormone release.
The adrenal glands have a large blood supply. They receive arterial blood from the renal arteries,
the phrenic arteries, and suprarenal arteries from the aorta. Arterial blood enters the adrenal glands
at the adrenal cortex and drains into venules in the adrenal medulla. The suprarenal vein of the right
adrenal gland drains into the inferior vena cava, and the suprarenal vein of the left adrenal gland
drains into the left renal vein.
Chromaffin cells of the adrenal medulla produce epinephrine (adrenaline) and norepinephrine
(noradrenaline). Epinephrine is the primary adrenal medulla hormone accounting for 75 to 80% of
its secretions. Epinephrine and norepinephrine increase heart rate, breathing rate, cardiac muscle
contractions, and blood glucose levels. They also accelerate the breakdown of glucose in skeletal
muscles and stored fats in adipose tissue.
fatty acids from adipose tissue. These hormones increase blood glucose levels to maintain levels
within a normal range between meals. They are secreted in response to ACTH, and levels are
regulated by negative feedback.
Cortisol (lifesaving hormone): Secreted by zona fasciculata, also known as hydrocorticosterone.
Cortisol has a small amount of mineralocorticoid activity.
Cortisol (i) increases sugar in blood causing hyperglycemia, (ii) causes protein lysis in some organs
like lymphoid tissues (thymus, lymph node etc), muscles, bones, skin etc. Deamination & urea
formation stimulate or inhibit protein synthesis, (iii) facilitates lipolysis and promotes deposition of
fat, in unusual sites of the body, (iv) inhibit nucleic acid synthesis in all other tissues except liver
where RNA synthesis increases, (v) prevent WBC actions and collagen fibres in tissues (anti-
inflammatory hormone) and thus, used in diseases like edema, arthritis/rheumatism, (vi) checks
immune reactions by antibodies (immuno-suppressive) and (vii) used in transplantation of organs.
C. Androgens
Androgens are a class of hormones and that affect sexual characteristics. Testosterone is associated
with male sexual characteristics, while progesterone and estrogen are associated with female
reproductive function: androstenedione is an intermediate molecule in the synthetic pathways of
these and many of the steroid hormones.
These hormones stimulate the muscles, external genitalia and sexual behaviour. Male hormone
secreted is mainly dehydroepiandrosterone [DHEA].
In situations where the gonads are not functioning the progesterone made in the adrenal glands
does influence sexual characteristics. One of the reasons why post menopausal women develop
more male characteristics is that the progesterone their adrenal makes gets converted to testosterone.
5.6.2 Adrenal medulla
The adrenal medulla is the inner layer of the adrenal glands and contains chromaffin cells, which
are large, irregularly shaped cells that are closely associated with blood vessels. These cells are
innervated by autonomic (involuntary) nerve fibers from the central nervous system, which allows
for quick hormone release.
The adrenal glands have a large blood supply. They receive arterial blood from the renal arteries,
the phrenic arteries, and suprarenal arteries from the aorta. Arterial blood enters the adrenal glands
at the adrenal cortex and drains into venules in the adrenal medulla. The suprarenal vein of the right
adrenal gland drains into the inferior vena cava, and the suprarenal vein of the left adrenal gland
drains into the left renal vein.
Chromaffin cells of the adrenal medulla produce epinephrine (adrenaline) and norepinephrine
(noradrenaline). Epinephrine is the primary adrenal medulla hormone accounting for 75 to 80% of
its secretions. Epinephrine and norepinephrine increase heart rate, breathing rate, cardiac muscle
contractions, and blood glucose levels. They also accelerate the breakdown of glucose in skeletal
muscles and stored fats in adipose tissue.
131
Both are stored in vesicles or granules in the adrenal medulla, very similar to the way posterior
pituitary cells store the neurosecretory hormones from hypothalamus for release. The release of
epinephrine and norepinephrine into the blood is stimulated by neural impulses from the sympathetic
nervous system. These neural impulses originate from the hypothalamus in response to stress to
prepare the body for the fight or flight response.
Functions of epinephrine:
Constricts blood vessels of skin
Enhances blood flow by vasodilation of blood vessels of brain, heart, liver and skeletal muscles.
Increases heartbeat, BP, BMR and amount of glucose in blood.
Stimulates trachea and bronchi muscles to relax, increasing the rate of breathing thus, helps
in curing asthma.
Dilates pupils, constricts the erecter pilli muscle of hair and goose flesh are observed.
Stimulates contraction in spleen to pour off stored blood into the blood stream.
Checks the secretion of saliva and reduces peristaltic movement in alimentary canal.
Reduces the clotting period of blood, stimulates uterus to contract.
Norepinephrine acts as a vasoconstrictor, increasing BP. It doesn’t constrict the coronary artery of
heart.
5.6.3 Control of adrenal secretion
Adrenocorticotropic hormone [ACTH] of
anterior pituitary controls hormones of
adrenal cortex. ACTH controls very less or
even does not control mineralocorticoid
secretions. These are controlled by renin
secreted by kidneys. Nervous system
controls the secretions from adrenal
medulla. Cortisol and ACTH levels in blood
are maximum in morning and minimum in
the early part of night.
5.6.4 Disorders
A. Hyposecretion
Addison’s disease (hypoadren-
alism): Caused due to corticoid
hyposecretion, symptoms are
dehydration in the body, reduced BP,
BMR and body temperature,
increased excretion of water and Na
+
, skin of hands, neck and face turns bronze color.
Hypothalamus
CRF
ADH
Exogenous
ACTH
Metyrapone
mitotane
Renin-angiotensin
system
Adrenal
cortex
Glucocorticoids Mineralocorticoids
Exogenous glucocorticoids (eg. prednisolone)
Exogenous mineralocorticoids
(eg. fludrocortisone)
Peripheral actions (metabolic, anti- inflammatory, immunosuppressive)
Peripheral actions on salt and water metabolism
++
+
Anterior pituitary
ACTH
+
-
-
+
Long negative feedback loop
-
--
+
Short negative
feedback loop
-
+ +
+ +
Both are stored in vesicles or granules in the adrenal medulla, very similar to the way posterior
pituitary cells store the neurosecretory hormones from hypothalamus for release. The release of
epinephrine and norepinephrine into the blood is stimulated by neural impulses from the sympathetic
nervous system. These neural impulses originate from the hypothalamus in response to stress to
prepare the body for the fight or flight response.
Functions of epinephrine:
Constricts blood vessels of skin
Enhances blood flow by vasodilation of blood vessels of brain, heart, liver and skeletal muscles.
Increases heartbeat, BP, BMR and amount of glucose in blood.
Stimulates trachea and bronchi muscles to relax, increasing the rate of breathing thus, helps
in curing asthma.
Dilates pupils, constricts the erecter pilli muscle of hair and goose flesh are observed.
Stimulates contraction in spleen to pour off stored blood into the blood stream.
Checks the secretion of saliva and reduces peristaltic movement in alimentary canal.
Reduces the clotting period of blood, stimulates uterus to contract.
Norepinephrine acts as a vasoconstrictor, increasing BP. It doesn’t constrict the coronary artery of
heart.
5.6.3 Control of adrenal secretion
Adrenocorticotropic hormone [ACTH] of
anterior pituitary controls hormones of
adrenal cortex. ACTH controls very less or
even does not control mineralocorticoid
secretions. These are controlled by renin
secreted by kidneys. Nervous system
controls the secretions from adrenal
medulla. Cortisol and ACTH levels in blood
are maximum in morning and minimum in
the early part of night.
5.6.4 Disorders
A. Hyposecretion
Addison’s disease (hypoadren-
alism): Caused due to corticoid
hyposecretion, symptoms are
dehydration in the body, reduced BP,
BMR and body temperature,
increased excretion of water and Na
+
, skin of hands, neck and face turns bronze color.
Hypothalamus
CRF
ADH
Exogenous
ACTH
Metyrapone
mitotane
Renin-angiotensin
system
Adrenal
cortex
Glucocorticoids Mineralocorticoids
Exogenous glucocorticoids (eg. prednisolone)
Exogenous mineralocorticoids
(eg. fludrocortisone)
Peripheral actions (metabolic, anti- inflammatory, immunosuppressive)
Peripheral actions on salt and water metabolism
++
+
Anterior pituitary
ACTH
+
-
-
+
Long negative feedback loop
-
--
+
Short negative
feedback loop
-
+ +
+ +
132
Hypoglycemia: Reduction in amount of glucose in blood, patient may die.
B. Hypersecretion
Cushing’s syndrome: Corticoid hypersecretion causes this; body broadens due to excess
deposition of fat under skin (to cause moon face, fish mouth and buffalo hump), protein
catabolism increases in body, irregular growth of skin and bones occurs.
Hyperglycemia: Amount of Na
+
and water increase in ECF i.e. edema. Due to this BP also
increases.
Conn’s disease (primary aldosteronism): Due to excess of mineralocorticoids, an imbalance
of Na
+
, K
+
is observed. There occurs irregularity in nervous system, as a result muscles get
contracted; muscle weakness, hypertension and hypokalemia are observed.
Secondary hyperaldosteronism: Blood pressure increases, excess mental tension and
weakness in muscles are observed.
Adrenogenital syndrome/Adrenal virilism/Pseudohermaphrodite: Girls develop male
characters eg. menstrual cycle is stopped, uterus and ovary are damaged and clitoris enlarges.
Gynaecomastia: If in a man, female sex hormone is in excess amount, he will show feminine
characters i.e. development of mammary glands.
Macrogenitosomia: If in a male, androgens are present in excess amount, it develops extra-
long penis.
TARGET POINTS
Eustachius discovered the adrenal glands that weigh about 4-6 g in man.
They are ectomesodermal in origin i.e. cortical portion (80-90%) develops from mesoderm
while medullar portion (10-20%) develops from neural-ectoderm of embryo. The whole adrenal
gland is surrounded by a fibrous capsule.
Adrenal gland is also known as 4 - s gland
S - Sugar metabolism
S - Salt retaining actions
S - Sex hormones
S - Stress reactions
4-S
Gonadocorticoids (sex hormones) are secreted in very small amount by zona reticularis.
Chromaffin cells/phaeochromocytes along with the preganglionic motor fibers of sympathetic
nervous system, compose the sympatheticoadrenal system.
Epinephrine and norepinephrine are collectively called catecholamines.
Walter Cannon termed epinephrine as the emergency hormone as it prepares the body for
unavoidable emergency situations.
Hypoglycemia: Reduction in amount of glucose in blood, patient may die.
B. Hypersecretion
Cushing’s syndrome: Corticoid hypersecretion causes this; body broadens due to excess
deposition of fat under skin (to cause moon face, fish mouth and buffalo hump), protein
catabolism increases in body, irregular growth of skin and bones occurs.
Hyperglycemia: Amount of Na
+
and water increase in ECF i.e. edema. Due to this BP also
increases.
Conn’s disease (primary aldosteronism): Due to excess of mineralocorticoids, an imbalance
of Na
+
, K
+
is observed. There occurs irregularity in nervous system, as a result muscles get
contracted; muscle weakness, hypertension and hypokalemia are observed.
Secondary hyperaldosteronism: Blood pressure increases, excess mental tension and
weakness in muscles are observed.
Adrenogenital syndrome/Adrenal virilism/Pseudohermaphrodite: Girls develop male
characters eg. menstrual cycle is stopped, uterus and ovary are damaged and clitoris enlarges.
Gynaecomastia: If in a man, female sex hormone is in excess amount, he will show feminine
characters i.e. development of mammary glands.
Macrogenitosomia: If in a male, androgens are present in excess amount, it develops extra-
long penis.
TARGET POINTS
Eustachius discovered the adrenal glands that weigh about 4-6 g in man.
They are ectomesodermal in origin i.e. cortical portion (80-90%) develops from mesoderm
while medullar portion (10-20%) develops from neural-ectoderm of embryo. The whole adrenal
gland is surrounded by a fibrous capsule.
Adrenal gland is also known as 4 - s gland
S - Sugar metabolism
S - Salt retaining actions
S - Sex hormones
S - Stress reactions
4-S
Gonadocorticoids (sex hormones) are secreted in very small amount by zona reticularis.
Chromaffin cells/phaeochromocytes along with the preganglionic motor fibers of sympathetic
nervous system, compose the sympatheticoadrenal system.
Epinephrine and norepinephrine are collectively called catecholamines.
Walter Cannon termed epinephrine as the emergency hormone as it prepares the body for
unavoidable emergency situations.
133
5.7 PANCREAS
The pancreas contains both exocrine cells that excrete digestive enzymes and endocrine cells that
release hormones. Approximately 99% of pancreatic cells are exocrine cells that are arranged around
ducts in clusters called acini (singular is acinus).
The endocrine cells of the pancreas from clusters called pancreatic islets or the islets of Langerhans
(islets are small islands) with associated blood capillaries. The pancreatic islets contain two major
cell types: alpha cells, which constitute 20% of the total mass of the islets and produce the hormone
glucagon and beta cells, which constitute 75% of the total mass of the islets and produce the
hormone insulin. These hormones regulate blood glucose levels. Alpha cells release glucagon as
blood glucose levels decline below the set point. When blood glucose level rise, alpha cells stop
secreting glucagon, and beta cells than release insulin. When blood glucose levels drop below the
set point (which does not happen under normal conditions), beta cells stop secreting insulin.
Pancreatic cells also contain two minor
populations of cells: delta cells, which
constitute 4% of the total mass of the islets
and secrete somatostatin, and F (or PP) cells,
which constitute 1% of the total mass of the
islets and secrete pancreatic polypeptide.
They have specific paracrine regulator effects
in the pancreas. Pancreatic polypeptide is
secreted after a high protein meal or fasting
and inhibits pancreatic exocrine secretion and stimulates gastric juice secretion (opposite effect of
cholecystokinin, CCK of the small intestine). It also stimulates both alpha and beta cells.
A. Insulin
Benting and Best first prepared insulin while its molecular structure was given by A. F. Sanger
(with the help of cow’s insulin). ‘Insulin’ was also termed by A. F. Sanger. Insulin is the first protein
that is artificially synthesized in lab and is crystallized. Human insulin was synthesized by Tsan.
One molecule of insulin is made of 51 amino acids that have 2 chains: (i) chain (made of 21 amino
acids) and (ii) chain (made of 30 amino acids). Both the branches and chains are bind together
with cross disulphide bonds. A. F. Sanger was awarded by Noble Prize for it.
Functions of insulin:
Actions on cell membrane permeability: Except brain cells, RBCs, retina, insulin stimulates
the permeability and consumption of glucose in all somatic cells.
Inhibits gluconeogenesis, promotes glycogenesis, enhances peripheral utilization (oxidation)
of glucose, causing the blood sugar level to fall, inhibits glycogenolysis.
Promotes lipogenesis, inhibits lipolysis and formation of ketone bodies.
Promotes protein synthesis by promoting uptake of amino acid by liver and muscle cell.
Pancreatic duct
Insulin-producing
cell
Exocrine
acinar cells
Blood capillary
Glucagon-producing cell
Somatostatin-
producing cell
Pancreatic polypeptide-
producing PP cell
5.7 PANCREAS
The pancreas contains both exocrine cells that excrete digestive enzymes and endocrine cells that
release hormones. Approximately 99% of pancreatic cells are exocrine cells that are arranged around
ducts in clusters called acini (singular is acinus).
The endocrine cells of the pancreas from clusters called pancreatic islets or the islets of Langerhans
(islets are small islands) with associated blood capillaries. The pancreatic islets contain two major
cell types: alpha cells, which constitute 20% of the total mass of the islets and produce the hormone
glucagon and beta cells, which constitute 75% of the total mass of the islets and produce the
hormone insulin. These hormones regulate blood glucose levels. Alpha cells release glucagon as
blood glucose levels decline below the set point. When blood glucose level rise, alpha cells stop
secreting glucagon, and beta cells than release insulin. When blood glucose levels drop below the
set point (which does not happen under normal conditions), beta cells stop secreting insulin.
Pancreatic cells also contain two minor
populations of cells: delta cells, which
constitute 4% of the total mass of the islets
and secrete somatostatin, and F (or PP) cells,
which constitute 1% of the total mass of the
islets and secrete pancreatic polypeptide.
They have specific paracrine regulator effects
in the pancreas. Pancreatic polypeptide is
secreted after a high protein meal or fasting
and inhibits pancreatic exocrine secretion and stimulates gastric juice secretion (opposite effect of
cholecystokinin, CCK of the small intestine). It also stimulates both alpha and beta cells.
A. Insulin
Benting and Best first prepared insulin while its molecular structure was given by A. F. Sanger
(with the help of cow’s insulin). ‘Insulin’ was also termed by A. F. Sanger. Insulin is the first protein
that is artificially synthesized in lab and is crystallized. Human insulin was synthesized by Tsan.
One molecule of insulin is made of 51 amino acids that have 2 chains: (i) chain (made of 21 amino
acids) and (ii) chain (made of 30 amino acids). Both the branches and chains are bind together
with cross disulphide bonds. A. F. Sanger was awarded by Noble Prize for it.
Functions of insulin:
Actions on cell membrane permeability: Except brain cells, RBCs, retina, insulin stimulates
the permeability and consumption of glucose in all somatic cells.
Inhibits gluconeogenesis, promotes glycogenesis, enhances peripheral utilization (oxidation)
of glucose, causing the blood sugar level to fall, inhibits glycogenolysis.
Promotes lipogenesis, inhibits lipolysis and formation of ketone bodies.
Promotes protein synthesis by promoting uptake of amino acid by liver and muscle cell.
Pancreatic duct
Insulin-producing
cell
Exocrine
acinar cells
Blood capillary
Glucagon-producing cell
Somatostatin-
producing cell
Pancreatic polypeptide-
producing PP cell
134
Promotes synthesis of DNA and RNA.
Affects BMR in cells.
Hyposecretion
Diabetes mellitus: Body cells cannot use the sugar stored in blood, thereby increasing the
sugar content in blood beyond the normal concentration.
Glycosuria: Glucose is excreted through urine if amount of glucose (up to >180 mg/dl) is
excess in blood. The amount of water increases (in this stage) in the urine, so intervals of
urination reduces, it is called polyuria.
Polydipsia: Due to excess excretion of urine (urination at short intervals) probability of
dehydration is enhanced. The patient feels thirsty, and there is a continuous loss of electrolytes
from the body, polyphagia: excessive hunger.
Due to active and incomplete decomposition of fats in fatty tissues, ketone bodies are formed.
These ketone bodies are acetone, aceto acetic acid and beta hydroxy butyrate. Due to
increased amount of these ketone bodies ketoacidosis starts in the body. These bodies are
poisonous.
The combined effect of ketoacidosis, dehydration and hyperglycemia may cause diabetic
comma to the patient, patient becomes unconscious and even may die.
Insulin hormone is given to the patient by injection in this disease, insulin given orally is not
effective, because it digest in the alimentary canal like protein.
Now a days, oral insulin is used in following states:
A. IZS: insulin zinc suspension.
B. PZI: Protamine zinc insulin.
Hypersecretion
Hypoglycemia: Hypersecretion of insulin decreases glucose level in blood. Body cells take
more and more glucose from blood, depriving the glucose need of nervous system, retina,
genital epithelium, as a result the patient loses its reproductive power and sight. Due to excess
irritation in brain cells, patient feels exhausted, unconsciousness, cramps, and at last he may
die.
Insulin shock: During physical labor or fasting, if a diabetic patient takes an insulin injection,
sugar level in blood reduces quickly up to 40 mg/100ml of blood. The patient may be
unconscious or may even die.
B. Glucagon
Kimball and Murlin discovered glucagon, a hyperglycemia factor. It is made of chains of polypeptide
29 amino acids and is antagonistic to insulin. It is secreted when the sugar level of blood reduces.
Promotes synthesis of DNA and RNA.
Affects BMR in cells.
Hyposecretion
Diabetes mellitus: Body cells cannot use the sugar stored in blood, thereby increasing the
sugar content in blood beyond the normal concentration.
Glycosuria: Glucose is excreted through urine if amount of glucose (up to >180 mg/dl) is
excess in blood. The amount of water increases (in this stage) in the urine, so intervals of
urination reduces, it is called polyuria.
Polydipsia: Due to excess excretion of urine (urination at short intervals) probability of
dehydration is enhanced. The patient feels thirsty, and there is a continuous loss of electrolytes
from the body, polyphagia: excessive hunger.
Due to active and incomplete decomposition of fats in fatty tissues, ketone bodies are formed.
These ketone bodies are acetone, aceto acetic acid and beta hydroxy butyrate. Due to
increased amount of these ketone bodies ketoacidosis starts in the body. These bodies are
poisonous.
The combined effect of ketoacidosis, dehydration and hyperglycemia may cause diabetic
comma to the patient, patient becomes unconscious and even may die.
Insulin hormone is given to the patient by injection in this disease, insulin given orally is not
effective, because it digest in the alimentary canal like protein.
Now a days, oral insulin is used in following states:
A. IZS: insulin zinc suspension.
B. PZI: Protamine zinc insulin.
Hypersecretion
Hypoglycemia: Hypersecretion of insulin decreases glucose level in blood. Body cells take
more and more glucose from blood, depriving the glucose need of nervous system, retina,
genital epithelium, as a result the patient loses its reproductive power and sight. Due to excess
irritation in brain cells, patient feels exhausted, unconsciousness, cramps, and at last he may
die.
Insulin shock: During physical labor or fasting, if a diabetic patient takes an insulin injection,
sugar level in blood reduces quickly up to 40 mg/100ml of blood. The patient may be
unconscious or may even die.
B. Glucagon
Kimball and Murlin discovered glucagon, a hyperglycemia factor. It is made of chains of polypeptide
29 amino acids and is antagonistic to insulin. It is secreted when the sugar level of blood reduces.
135
Glucagon increases sugar conc. in blood, stimulates gluconeogenesis in liver (thereby, increasing
glucose level in blood), stimulates lipolysis of fats in fatty tissues, decomposes glycogen into glucose
in liver i.e. it stimulates glycogenolysis in liver.
Secretion of insulin and glucagon is controlled by a limit control feedback. When sugar conc. increases
in blood, insulin is secreted and as a result, when sugar conc. reduces, glucagon is secreted.
C. Somatostatin: Regulates the secretion of insulin and glucagon.
TARGET POINTS
Two major sites of glycogenesis are liver and the muscles.
Normal concentration of sugar in blood is 90-110 mg. per 100 ml. of blood.
World diabetes day - 14 November
5.8 GONADS
The gonads, the male testes (sing. Testis) and female ovaries, function in production of gametes
(sperm and ovum) and also produce steroid hormones. The testes produce androgens, testosterone
being the most prominent. Testosterone stimulates the development of male secondary sex
characteristics and the production of sperm cells. The testes also produce the hormone inhibin,
which inhibits the release of the tropic hormone from the anterior pituitary follicle stimulating hormone
(FSH) needed for the development of sperm (spermatogenesis).
The ovaries produce the hormones estrogen and progesterone, which stimulate the development
of female secondary sex characteristics, regulate the menstrual cycle, and prepare the body for
childbirth. The ovaries also produce the hormone inhibin, which inhibits the release of FSH.
The placenta, which supplies the necessary nutrients to the fetus, is also an endocrine organ. It
synthesizes and secretes a number of hormones that are crucial for the maintenance of pregnancy.
The human chorionic gonadotropin hormone (hCG), that is the basis of urine pregnancy tests is
another of the placental hormones. As the fetus develops, the placenta takes over the production of
estrogen and progesterone to maintain pregnancy. The high level of estrogen facilitates the growth
of the uterus and the mammary glands during gestation. Progesterone is important in suppressing
maternal immune response towards the fetus and inhibiting uterine smooth muscle contraction.
The placenta also produces relaxin, which affects collagen metabolism and softens the pubic
symphysis to facilitate birthing. It also produces lactogen, which is structurally similar to prolactin
and growth hormone (pituitary hormone), but its role, if any, in humans lactation is still being
investigated.
5.9 ORGANS WITH SECONDARY ENDOCRINE FUNCTION
There are several organs whose primary functions are non-endocrine but that also possess endocrine
functions. These include the heart, gastrointestinal tract, kidneys, adipose tissue and skin.
Glucagon increases sugar conc. in blood, stimulates gluconeogenesis in liver (thereby, increasing
glucose level in blood), stimulates lipolysis of fats in fatty tissues, decomposes glycogen into glucose
in liver i.e. it stimulates glycogenolysis in liver.
Secretion of insulin and glucagon is controlled by a limit control feedback. When sugar conc. increases
in blood, insulin is secreted and as a result, when sugar conc. reduces, glucagon is secreted.
C. Somatostatin: Regulates the secretion of insulin and glucagon.
TARGET POINTS
Two major sites of glycogenesis are liver and the muscles.
Normal concentration of sugar in blood is 90-110 mg. per 100 ml. of blood.
World diabetes day - 14 November
5.8 GONADS
The gonads, the male testes (sing. Testis) and female ovaries, function in production of gametes
(sperm and ovum) and also produce steroid hormones. The testes produce androgens, testosterone
being the most prominent. Testosterone stimulates the development of male secondary sex
characteristics and the production of sperm cells. The testes also produce the hormone inhibin,
which inhibits the release of the tropic hormone from the anterior pituitary follicle stimulating hormone
(FSH) needed for the development of sperm (spermatogenesis).
The ovaries produce the hormones estrogen and progesterone, which stimulate the development
of female secondary sex characteristics, regulate the menstrual cycle, and prepare the body for
childbirth. The ovaries also produce the hormone inhibin, which inhibits the release of FSH.
The placenta, which supplies the necessary nutrients to the fetus, is also an endocrine organ. It
synthesizes and secretes a number of hormones that are crucial for the maintenance of pregnancy.
The human chorionic gonadotropin hormone (hCG), that is the basis of urine pregnancy tests is
another of the placental hormones. As the fetus develops, the placenta takes over the production of
estrogen and progesterone to maintain pregnancy. The high level of estrogen facilitates the growth
of the uterus and the mammary glands during gestation. Progesterone is important in suppressing
maternal immune response towards the fetus and inhibiting uterine smooth muscle contraction.
The placenta also produces relaxin, which affects collagen metabolism and softens the pubic
symphysis to facilitate birthing. It also produces lactogen, which is structurally similar to prolactin
and growth hormone (pituitary hormone), but its role, if any, in humans lactation is still being
investigated.
5.9 ORGANS WITH SECONDARY ENDOCRINE FUNCTION
There are several organs whose primary functions are non-endocrine but that also possess endocrine
functions. These include the heart, gastrointestinal tract, kidneys, adipose tissue and skin.
136
A. Heart and cardiovascular system
The heart possesses specialized cardiac muscle cells, which are endocrine cells in the walls of the
atria. These cells respond to increased blood volume by releasing the hormone atrial natriuretic
peptide (ANP). Natrium is the name for sodium in many languages and is the reason that Na is the
chemical symbol for sodium. High blood volume causes the cells to be stretched, opening stretch
activated membrane channels, resulting in hormone release. ANP acts on the kidneys to reduce the
reabsorption of Na
+
, causing Na
+
and water to be excreted in the urine. ANP also reduces the
amounts of renin released by the kidneys and aldosterone released by the adrenal cortex, further
preventing the retention of water. In this way, ANP reduces the concentration of Na
+
in the blood and
causes a reduction in blood volume and blood pressure. Another natriuretic hormone, BNP (misnamed
brain natriuretic because it was first isolated from pig brains) from the heart ventricle, enhances the
effect of ANP.
Endothelial cells lining the cardiovascular system also have an endocrine function. They produce
paracrine endothelin, a vasodilator and stimulator of ANP secretion, and nitric oxide (NO), a
vasodilator and inhibitor of ANP secretion.
B. Digestive system
The digestive system produces several hormones that aid in digestive and metabolic homeostasis.
Endocrine cells are located in the mucosa of the GI tract throughout the stomach and small intestine.
Hormone secretion is controlled by receptors monitoring the chemical content of the digestive lumen.
Some of the hormones produced include gastrin (from stomach), secretin, and cholecystokinin
CCK (from small intestine) that act on the GI tract and accessory organs such as the pancreas, gall
bladder, and liver. They trigger the release of digestive juices that help to break down and digest
food in the GI tract. The GI tract also produces the hormones glucose dependent insulinotropic
peptide (GIP) (from stomach) and glucagon like peptide 1(GLP-1) (from small intestine). These
hormones are secreted in response to glucose in the intestinal lumen. GIP and GLP – 1 target cells
are beta cells in the pancreas, which are stimulated to release insulin and alpha cells that are
inhibited from releasing glucagon. The stomach also produces ghrelin that mediates hunger,
stimulating appetite and growth hormone release.
The liver, as an accessory organ of the digestive system, also has an endocrine function in production
of insulin like growth factor (IGFs) and Thrombopoietin (THPO). IGFs work with growth hormone
to regulate cell metabolism while THPO triggers the formation of platelets in the blood. The liver
also produces prohormones (angiotensinogen and calcidiol, vitamin D) and plasma protein that
transport many of the hormones.
C. Kidneys and urinary system
The adrenal glands associated with the kidneys are major endocrine glands, and the kidneys
themselves also possess endocrine functions. Renin (‘renal’ generally describes aspects of the
kidney) is released in response to decreased blood volume or pressure and is part of the renin
angiotensin system that is responsible for formation of angiotensin II and ultimately leads to the
A. Heart and cardiovascular system
The heart possesses specialized cardiac muscle cells, which are endocrine cells in the walls of the
atria. These cells respond to increased blood volume by releasing the hormone atrial natriuretic
peptide (ANP). Natrium is the name for sodium in many languages and is the reason that Na is the
chemical symbol for sodium. High blood volume causes the cells to be stretched, opening stretch
activated membrane channels, resulting in hormone release. ANP acts on the kidneys to reduce the
reabsorption of Na
+
, causing Na
+
and water to be excreted in the urine. ANP also reduces the
amounts of renin released by the kidneys and aldosterone released by the adrenal cortex, further
preventing the retention of water. In this way, ANP reduces the concentration of Na
+
in the blood and
causes a reduction in blood volume and blood pressure. Another natriuretic hormone, BNP (misnamed
brain natriuretic because it was first isolated from pig brains) from the heart ventricle, enhances the
effect of ANP.
Endothelial cells lining the cardiovascular system also have an endocrine function. They produce
paracrine endothelin, a vasodilator and stimulator of ANP secretion, and nitric oxide (NO), a
vasodilator and inhibitor of ANP secretion.
B. Digestive system
The digestive system produces several hormones that aid in digestive and metabolic homeostasis.
Endocrine cells are located in the mucosa of the GI tract throughout the stomach and small intestine.
Hormone secretion is controlled by receptors monitoring the chemical content of the digestive lumen.
Some of the hormones produced include gastrin (from stomach), secretin, and cholecystokinin
CCK (from small intestine) that act on the GI tract and accessory organs such as the pancreas, gall
bladder, and liver. They trigger the release of digestive juices that help to break down and digest
food in the GI tract. The GI tract also produces the hormones glucose dependent insulinotropic
peptide (GIP) (from stomach) and glucagon like peptide 1(GLP-1) (from small intestine). These
hormones are secreted in response to glucose in the intestinal lumen. GIP and GLP – 1 target cells
are beta cells in the pancreas, which are stimulated to release insulin and alpha cells that are
inhibited from releasing glucagon. The stomach also produces ghrelin that mediates hunger,
stimulating appetite and growth hormone release.
The liver, as an accessory organ of the digestive system, also has an endocrine function in production
of insulin like growth factor (IGFs) and Thrombopoietin (THPO). IGFs work with growth hormone
to regulate cell metabolism while THPO triggers the formation of platelets in the blood. The liver
also produces prohormones (angiotensinogen and calcidiol, vitamin D) and plasma protein that
transport many of the hormones.
C. Kidneys and urinary system
The adrenal glands associated with the kidneys are major endocrine glands, and the kidneys
themselves also possess endocrine functions. Renin (‘renal’ generally describes aspects of the
kidney) is released in response to decreased blood volume or pressure and is part of the renin
angiotensin system that is responsible for formation of angiotensin II and ultimately leads to the
137
release of aldosterone. Both angiotensin II and aldosterone then causes the retention of Na
+
and
water, raising blood volume. The kidneys also release the steroid hormone calcitriol, which is the
biologically active form of vitamin D that aids in the absorption of Ca
2+
. Erythropoietin (EPO) is a
protein hormone that triggers the formation of red blood cells in the bone marrow. EPO is released
in response to low oxygen levels. Because red blood cells are oxygen carriers, increased production
results in greater oxygen delivery throughout the body. The banned substance EPO had been used
by athletes at one point to improve performance, as greater oxygen delivery to muscle cells allows
for greater endurance. Because red blood cells increase the viscosity of blood, artificially high levels
can cause severe health risks.
D. Adipose Tissue
Adipose tissue produces the hormone leptin in response to food intake. Leptin binds to neuropeptide
Y in the CNS neurons, producing a feeling of satiety after eating, thus affecting appetite and reducing
the urge for further eating. Note that it has the opposite effect of ghrelin secretion from the stomach,
but when leptin levels drop, the brain detects a state of starvation and the feeling of hunger increases.
These two hormones are the subject of much research related to obesity.
E. Skin
Skin produces Cholecalciferol, which is an inactive hormone form of vitamin D
3
. It is formed when
cholesterol molecules in the skin, in the form of 7 dehydrocholesterol, are exposed to ultraviolet
radiation. Cholecalciferol then enters the bloodstream and is modified in the liver to form calcifediol.
Calcefediol is then modified in the kidneys to form calcitriol, which is the active form of vitamin D
3
.
Vitamin D plays an important role in bone formation.
Rickets is observed in children due to the deficiency of vitamin D as a result of which bones become
weak, thin, deshaped and ugly.
In adulthood, its deficiency causes osteomalacia. Bones become weak and brittle.
F. Bone
Bones not only respond to hormones to maintain blood calcium homeostasis, but recent research
shows they also have an endocrine function. Osteocytes have been found to produce two hormones
(fibroblast growth factor 23 and osteocalcin) that act on kidney, pancreas and other body tissues
influencing vitamin D and glucose homeostasis.
release of aldosterone. Both angiotensin II and aldosterone then causes the retention of Na
+
and
water, raising blood volume. The kidneys also release the steroid hormone calcitriol, which is the
biologically active form of vitamin D that aids in the absorption of Ca
2+
. Erythropoietin (EPO) is a
protein hormone that triggers the formation of red blood cells in the bone marrow. EPO is released
in response to low oxygen levels. Because red blood cells are oxygen carriers, increased production
results in greater oxygen delivery throughout the body. The banned substance EPO had been used
by athletes at one point to improve performance, as greater oxygen delivery to muscle cells allows
for greater endurance. Because red blood cells increase the viscosity of blood, artificially high levels
can cause severe health risks.
D. Adipose Tissue
Adipose tissue produces the hormone leptin in response to food intake. Leptin binds to neuropeptide
Y in the CNS neurons, producing a feeling of satiety after eating, thus affecting appetite and reducing
the urge for further eating. Note that it has the opposite effect of ghrelin secretion from the stomach,
but when leptin levels drop, the brain detects a state of starvation and the feeling of hunger increases.
These two hormones are the subject of much research related to obesity.
E. Skin
Skin produces Cholecalciferol, which is an inactive hormone form of vitamin D
3
. It is formed when
cholesterol molecules in the skin, in the form of 7 dehydrocholesterol, are exposed to ultraviolet
radiation. Cholecalciferol then enters the bloodstream and is modified in the liver to form calcifediol.
Calcefediol is then modified in the kidneys to form calcitriol, which is the active form of vitamin D
3
.
Vitamin D plays an important role in bone formation.
Rickets is observed in children due to the deficiency of vitamin D as a result of which bones become
weak, thin, deshaped and ugly.
In adulthood, its deficiency causes osteomalacia. Bones become weak and brittle.
F. Bone
Bones not only respond to hormones to maintain blood calcium homeostasis, but recent research
shows they also have an endocrine function. Osteocytes have been found to produce two hormones
(fibroblast growth factor 23 and osteocalcin) that act on kidney, pancreas and other body tissues
influencing vitamin D and glucose homeostasis.
138
1. The hormone which is produced at the end
of gestation period is
a) Relaxin b) Oxytocin
c) Oestrogen d) Prolactin
2. Immune disease in which, body destroys the
ill functioning thyroid is
a) Simmond’s disease
b) Cretinism
c) Hashimoto’s disease
d) Myxoedema
3. Which one is correctly matched?
a) Relaxin – Gigantism
b) Prolactin – Cretinism
c) Parathyroid hormone – Tetany
d) Insulin – Diabetes insipidus
4. Which glands are indicated as A, B and C
in the given figure?
Corticotropin releasing hormone (CRH)
Adrenocorticotropin (ACTH)
Corticol
A
B
C Inhibits
a) A - Hypothalamus, B – Anterior pituitary,
C – Adrenal cortex
b) A – Hypothalamus, B – Anterior pituitary,
C – Posterior pituitary
c) A – Pituitary, B – Thyroid, C – Pineal
d) A – Pituitary, B – Thyroid, C – Parathyroid
Simple Questions
5. Sertoli cells are regulated by the pituitary
hormone known as
a) FSH b) GH
c) Prolactin d) LH
76) Which one is correct match?
a) Luteinizing hormone – Failure ovulation
b) Insulin – Diabetes insipidus
c) Parathormone – Diabetes mellitus
d) Thyroxine – Tetany
7. The functioning of adrenal medulla gland is
similar to those of nerves because adrenal
medulla
a) And nervous system are derived from
embryonic mesoderm
b) And nerves secrete similar chemicals
such as adrenaline and noradrenaline
c) Does not secrete any hormone
d) Is made up of nervous tissue
8. Herring bodies are found in
a) Neuro hypophysis
b) Adeno hypophysis
c) Both
d) None
9. Which is not a symptom of exophthalmic
goitre?
a) Degenerating sex organs
b) Protrusion of eyeball
c) Frightened look to the patient
d) None of the above
10. Both organs of which set secretes
hormones
a) Spleen – brain
b) Intestine – pancreas
c) Spleen – liver
d) Testes – placenta
1. The hormone which is produced at the end
of gestation period is
a) Relaxin b) Oxytocin
c) Oestrogen d) Prolactin
2. Immune disease in which, body destroys the
ill functioning thyroid is
a) Simmond’s disease
b) Cretinism
c) Hashimoto’s disease
d) Myxoedema
3. Which one is correctly matched?
a) Relaxin – Gigantism
b) Prolactin – Cretinism
c) Parathyroid hormone – Tetany
d) Insulin – Diabetes insipidus
4. Which glands are indicated as A, B and C
in the given figure?
Corticotropin releasing hormone (CRH)
Adrenocorticotropin (ACTH)
Corticol
A
B
C Inhibits
a) A - Hypothalamus, B – Anterior pituitary,
C – Adrenal cortex
b) A – Hypothalamus, B – Anterior pituitary,
C – Posterior pituitary
c) A – Pituitary, B – Thyroid, C – Pineal
d) A – Pituitary, B – Thyroid, C – Parathyroid
Simple Questions
5. Sertoli cells are regulated by the pituitary
hormone known as
a) FSH b) GH
c) Prolactin d) LH
76) Which one is correct match?
a) Luteinizing hormone – Failure ovulation
b) Insulin – Diabetes insipidus
c) Parathormone – Diabetes mellitus
d) Thyroxine – Tetany
7. The functioning of adrenal medulla gland is
similar to those of nerves because adrenal
medulla
a) And nervous system are derived from
embryonic mesoderm
b) And nerves secrete similar chemicals
such as adrenaline and noradrenaline
c) Does not secrete any hormone
d) Is made up of nervous tissue
8. Herring bodies are found in
a) Neuro hypophysis
b) Adeno hypophysis
c) Both
d) None
9. Which is not a symptom of exophthalmic
goitre?
a) Degenerating sex organs
b) Protrusion of eyeball
c) Frightened look to the patient
d) None of the above
10. Both organs of which set secretes
hormones
a) Spleen – brain
b) Intestine – pancreas
c) Spleen – liver
d) Testes – placenta
139
11. In Rabbit, which of the following organ acts
as both endocrine and exocrine gland?
a) Testes b) Ovary
c) Pancreas d) Stomach
12. In Hashimoto’s disease symptoms develop
like
a) Hyposecretion of thyroxine
b) Hypersecretion of thyroxine
c) Hyposecretion of adrenalin
d) None of the above
13. Hypokalemia means
a) High level of potassium in blood
b) High level of sodium in blood
c) Low level of potassium in blood
d) Low level of sodium in blood
14. Pineal body originates from
a) Dorsal part of diencephalon
b) Ventral part of diencephalon
c) Ventral part of cerebellum
d) Dorsal part of cerebellum
15. Conn’s disease is due to
a) Hyposecretion of aldosterone
b) Hypersecretion of aldosterone
c) Hyposecretion of STH
d) None of the above
16. An overdose of intravenous insulin may lead
to the death of an individual due to an
a) Excessive increase of blood glucose
b) Excessive decrease of blood glucose
c) Inhibition of glucagon secretion
d) Over production of histamine
17. Vasopressin is responsible for
a) Controlling oogenesis
b) Regulating blood pressure and act on the
nephron tubules
c) Regulating formation of pigment
d) Controlling spermatogenesis
18. Placenta present in mammals acts as an
endocrine tissue and produces
a) Human chorionic gonadotropin
b) Oestrogen
c) Progesterone
d) Testosterone
19. Which of the following pair of the hormones
is responsible for the growth and maturation
of the Graffian Follicle?
a) GH – ADH b) ACTH – LH
c) FSH – LH d) FSH – LTH
20. The same hormone can be known by
various names given in which set
a) Secretin, enterokinin, gastrin
b) Gametokinetic factor, testosterone, LTH
c) ADH, Pitressin and vasopressin
d) Oxytocin, tri iodothyronine, thyroxine
21. A healthy disorder that results from the
def iciency of thyroxine in adults is
characterized by
I) A low metabolic rate
II) Increase in body weight
III) Tendency to retain water in tissue is
a) Hypothyroidism b) Simple goiter
c) Myxoedema d) Cretinism
22. The blood calcium level is lowered by the
deficiency of
a) Both calcitonin and Parathormone
b) Calcitonin
c) Parathormone
d) Thyroxine
23. Parathormone controls
a) Fatty acid metabolism
b) Sodium and potassium metabolism
c) Calcium and phosphate metabolism
d) Protein metabolism
11. In Rabbit, which of the following organ acts
as both endocrine and exocrine gland?
a) Testes b) Ovary
c) Pancreas d) Stomach
12. In Hashimoto’s disease symptoms develop
like
a) Hyposecretion of thyroxine
b) Hypersecretion of thyroxine
c) Hyposecretion of adrenalin
d) None of the above
13. Hypokalemia means
a) High level of potassium in blood
b) High level of sodium in blood
c) Low level of potassium in blood
d) Low level of sodium in blood
14. Pineal body originates from
a) Dorsal part of diencephalon
b) Ventral part of diencephalon
c) Ventral part of cerebellum
d) Dorsal part of cerebellum
15. Conn’s disease is due to
a) Hyposecretion of aldosterone
b) Hypersecretion of aldosterone
c) Hyposecretion of STH
d) None of the above
16. An overdose of intravenous insulin may lead
to the death of an individual due to an
a) Excessive increase of blood glucose
b) Excessive decrease of blood glucose
c) Inhibition of glucagon secretion
d) Over production of histamine
17. Vasopressin is responsible for
a) Controlling oogenesis
b) Regulating blood pressure and act on the
nephron tubules
c) Regulating formation of pigment
d) Controlling spermatogenesis
18. Placenta present in mammals acts as an
endocrine tissue and produces
a) Human chorionic gonadotropin
b) Oestrogen
c) Progesterone
d) Testosterone
19. Which of the following pair of the hormones
is responsible for the growth and maturation
of the Graffian Follicle?
a) GH – ADH b) ACTH – LH
c) FSH – LH d) FSH – LTH
20. The same hormone can be known by
various names given in which set
a) Secretin, enterokinin, gastrin
b) Gametokinetic factor, testosterone, LTH
c) ADH, Pitressin and vasopressin
d) Oxytocin, tri iodothyronine, thyroxine
21. A healthy disorder that results from the
def iciency of thyroxine in adults is
characterized by
I) A low metabolic rate
II) Increase in body weight
III) Tendency to retain water in tissue is
a) Hypothyroidism b) Simple goiter
c) Myxoedema d) Cretinism
22. The blood calcium level is lowered by the
deficiency of
a) Both calcitonin and Parathormone
b) Calcitonin
c) Parathormone
d) Thyroxine
23. Parathormone controls
a) Fatty acid metabolism
b) Sodium and potassium metabolism
c) Calcium and phosphate metabolism
d) Protein metabolism
140
24. Cretinism is due to abnormal secretion of
a) Thyroid stimulating hormone
b) Thyroxine
c) Calcitonin
d) Parathormone
25. Gull’s disease is related to deficient working
of
a) Thyroid b) Parathyroid
c) Adrenal cortex d) Gonads
26. Identify from the following, a hormone
produced by the pituitary gland in both
males and females but functional only in
females
a) Vasopressin
b) Relaxin
c) Prolactin
d) Somatotropic hormone
27. Function of thyrocalcitonin
a) To reduce the calcium level in blood
b) To increase the calcium level in blood
c) Oppose the action of thyroxine
d) Maturation of gonads
28. BMR and temperature of body is controlled
by which endocrine gland?
a) Adrenal cortex b) Thymus
c) Thyroid d) Pituitary
29. Who isolated thyroxine hormone?
a) Best and Banting
b) F. Sanger
c) William Buemont
d) E.C. Kendall
30. After ovulation, ruptured follicle secrete
hormone that helps in
a) Libido
b) Growth of facial hair
c) High pitch voice
d) Pregnancy support
31. Find out the correct labelling of the given
figure
A
B
C
E
D
a) A – adenohypophysis, B – Pars
intermedia, C – Hypothalamus, D –
Infundibulum, E – Neurohypophysis.
b) A – Neurohypophysis, B – Pars
intermedia, C – Hypothalamus, D –
Infundibulum, E – adenohypophysis .
c) A – adenohypophysis, B – Infundibulum,
C – Hypothalamus, D – Pars intermedia,
E – Neurohypophysis.
d) A – Neurohypophysis, B –Infundibulum,
C – Hypothalamus, D –Pars intermedia,
E – adenohypophysis .
32. Insulin hormone was isolated in the
year____
a) 1910 b) 1922
c) 1925 d) 1948
33. The part of melanocyte stimulating hormone
(MSH) is secreted by the part of pituitary
a) Anterior lobe
b) Median lobe
c) Posterior lobe
d) Not any particular lobe
24. Cretinism is due to abnormal secretion of
a) Thyroid stimulating hormone
b) Thyroxine
c) Calcitonin
d) Parathormone
25. Gull’s disease is related to deficient working
of
a) Thyroid b) Parathyroid
c) Adrenal cortex d) Gonads
26. Identify from the following, a hormone
produced by the pituitary gland in both
males and females but functional only in
females
a) Vasopressin
b) Relaxin
c) Prolactin
d) Somatotropic hormone
27. Function of thyrocalcitonin
a) To reduce the calcium level in blood
b) To increase the calcium level in blood
c) Oppose the action of thyroxine
d) Maturation of gonads
28. BMR and temperature of body is controlled
by which endocrine gland?
a) Adrenal cortex b) Thymus
c) Thyroid d) Pituitary
29. Who isolated thyroxine hormone?
a) Best and Banting
b) F. Sanger
c) William Buemont
d) E.C. Kendall
30. After ovulation, ruptured follicle secrete
hormone that helps in
a) Libido
b) Growth of facial hair
c) High pitch voice
d) Pregnancy support
31. Find out the correct labelling of the given
figure
A
B
C
E
D
a) A – adenohypophysis, B – Pars
intermedia, C – Hypothalamus, D –
Infundibulum, E – Neurohypophysis.
b) A – Neurohypophysis, B – Pars
intermedia, C – Hypothalamus, D –
Infundibulum, E – adenohypophysis .
c) A – adenohypophysis, B – Infundibulum,
C – Hypothalamus, D – Pars intermedia,
E – Neurohypophysis.
d) A – Neurohypophysis, B –Infundibulum,
C – Hypothalamus, D –Pars intermedia,
E – adenohypophysis .
32. Insulin hormone was isolated in the
year____
a) 1910 b) 1922
c) 1925 d) 1948
33. The part of melanocyte stimulating hormone
(MSH) is secreted by the part of pituitary
a) Anterior lobe
b) Median lobe
c) Posterior lobe
d) Not any particular lobe
141
1. W hich one of the following pairs of
hormones are the examples of those that
can easily pass through the cell membrane
of the target cell and bind to a receptor inside
it (mostly in the nucleus)?
a) Insulin and glucagon
b) Thyroxin and insulin
c) Somatostatin and oxytocin
d) Cortisol and testosterone
2. Which is a bridge between nervous system
and endocrine system?
a) Thalamus
b) Hypothalamus
c) Limbic system
d) Parietal lobe
3. In human adult females oxytocin
a) Stimulates pituitary to secrete
vasopressin
b) Causes strong uterine contractions
during parturition
c) Is secreted by anterior pituitary
d) Stimulates growth of mammary glands
4. Tadpoles of frog can be made to grow as
giant sized tadpoles, if they are
a) Administered antithyroid substances like
thiourea
b) Administered large amounts of thyroxine
c) Reared on a diet rich in egg yolk
d) Reared on a diet rich in both egg yolk
and glucose
5. “Brain sand” is found in
a) Thyroid b) Thymus
c) Pineal body d) All
Difficult Questions
6. Match the following columns
Codes
A B C D A B C D
a) 2 1 4 3 b) 4 1 3 2
c) 3 2 4 1 d) 2 3 4 1
7.Assertion: Diabetes insipidus is marked by
excessive urination and too much thirst of
water.
Reason: Antidiuretic hormone (ADH) is
secreted by the posterior lobe of pituitary.
a) Both assertion and reason are true and
reason is the correct explanation of
assertion
b) Both assertion and reason are true, but
reason is not the correct explanation of
assertion
c) Assertion is true, but reason is false
d) Assertion is false, but reason is true
8. Which of the following hormones of the
human body regulate the blood calcium and
phosphate?
a) Glucagon
b) Growth hormone
c) Parathyroid hormone
d) Thyroxine
9. The most important component of the oral
contraceptive pills is
a) Progesterone
b) Growth hormone
c) Thyroxine
d) Luteinizing hormone
Column I Column II
A. ANF 1. Regulates blood calcium
levels
B. MSH 2. Decreases blood pressure
C. GIP 3. Pigmentation
D. TCT 4. Inhibits gastric secretion
1. W hich one of the following pairs of
hormones are the examples of those that
can easily pass through the cell membrane
of the target cell and bind to a receptor inside
it (mostly in the nucleus)?
a) Insulin and glucagon
b) Thyroxin and insulin
c) Somatostatin and oxytocin
d) Cortisol and testosterone
2. Which is a bridge between nervous system
and endocrine system?
a) Thalamus
b) Hypothalamus
c) Limbic system
d) Parietal lobe
3. In human adult females oxytocin
a) Stimulates pituitary to secrete
vasopressin
b) Causes strong uterine contractions
during parturition
c) Is secreted by anterior pituitary
d) Stimulates growth of mammary glands
4. Tadpoles of frog can be made to grow as
giant sized tadpoles, if they are
a) Administered antithyroid substances like
thiourea
b) Administered large amounts of thyroxine
c) Reared on a diet rich in egg yolk
d) Reared on a diet rich in both egg yolk
and glucose
5. “Brain sand” is found in
a) Thyroid b) Thymus
c) Pineal body d) All
Difficult Questions
6. Match the following columns
Codes
A B C D A B C D
a) 2 1 4 3 b) 4 1 3 2
c) 3 2 4 1 d) 2 3 4 1
7.Assertion: Diabetes insipidus is marked by
excessive urination and too much thirst of
water.
Reason: Antidiuretic hormone (ADH) is
secreted by the posterior lobe of pituitary.
a) Both assertion and reason are true and
reason is the correct explanation of
assertion
b) Both assertion and reason are true, but
reason is not the correct explanation of
assertion
c) Assertion is true, but reason is false
d) Assertion is false, but reason is true
8. Which of the following hormones of the
human body regulate the blood calcium and
phosphate?
a) Glucagon
b) Growth hormone
c) Parathyroid hormone
d) Thyroxine
9. The most important component of the oral
contraceptive pills is
a) Progesterone
b) Growth hormone
c) Thyroxine
d) Luteinizing hormone
Column I Column II
A. ANF 1. Regulates blood calcium
levels
B. MSH 2. Decreases blood pressure
C. GIP 3. Pigmentation
D. TCT 4. Inhibits gastric secretion
142
10. A pregnant female delivers a baby who
suffers from stunted growth, mental
retardation / low intelligence quotient and
abnormal skin. This is the result of
a) Low secretion of growth hormone
b) Cancer of the thyroid gland
c) Over secretion of pars distalis
d) Deficiency of iodine in diet
11. Select the answer which correctly matches
the endocrine gland with the hormone it
secretes and its function/ deficiency
symptom
12. In human, which side of cerebral
hemisphere recognizes the faces of friends
and family members?
a) Left cerebral hemisphere
b) Right cerebral hemisphere
c) Both (a) and (b)
d) None of the above
13. “Sella turcica” is a
a) Depression in skull enclosing pituitary
b) Cavity of skull enclosing ears
c) Covering of testis
d) Kind of endocrine glands
14. Identify the hormones, labelled as A, B and
C in the following figure
Hypothalamus
A
Pituitary
B C
Gonads
Gametes Sex hormones
a) A – GH, B – FSH, C – LH
b) A – GnRH, B – FSH, C – LH
c) A – GH, B – GnRH, C – PRT
d) A – GnRH, B – GH, C – PRT
15. Given below is an incomplete table about
certain hormones, their source glands and
one major effect of each on the body in
humans. Identify the correct option for the
three blanks A, B and C
Endocrine Hormone Function/Defiency
gland sympton
a) Posterior Growth Oversecretion
pituitary Hormone stimulates abnormal
(GH) growth
b) Thyroid Thyroxine Lack of iodine in
gland diet results in goitre
c) Corpus Testoste- Stimulates spermat-
luteum rone ogenesis
d) Anterior Oxytocin Stimulates uterus
pituitary contraction during
child birth
Gland Secretion Effect on body A Oestrogen Maintenance of
secondary sexual characters
Alpha cells of B Raises blood sugar
iselets of level
langerhans
Anterior C Over secretion
pituitary leads to gigantism
A B C
a) Placenta Insulin Vasopressin
b) Ovary Insulin Calcitonin
c) Placenta Glucagon Calcitonin
d) Ovary Glucagon Growth hormone
10. A pregnant female delivers a baby who
suffers from stunted growth, mental
retardation / low intelligence quotient and
abnormal skin. This is the result of
a) Low secretion of growth hormone
b) Cancer of the thyroid gland
c) Over secretion of pars distalis
d) Deficiency of iodine in diet
11. Select the answer which correctly matches
the endocrine gland with the hormone it
secretes and its function/ deficiency
symptom
12. In human, which side of cerebral
hemisphere recognizes the faces of friends
and family members?
a) Left cerebral hemisphere
b) Right cerebral hemisphere
c) Both (a) and (b)
d) None of the above
13. “Sella turcica” is a
a) Depression in skull enclosing pituitary
b) Cavity of skull enclosing ears
c) Covering of testis
d) Kind of endocrine glands
14. Identify the hormones, labelled as A, B and
C in the following figure
Hypothalamus
A
Pituitary
B C
Gonads
Gametes Sex hormones
a) A – GH, B – FSH, C – LH
b) A – GnRH, B – FSH, C – LH
c) A – GH, B – GnRH, C – PRT
d) A – GnRH, B – GH, C – PRT
15. Given below is an incomplete table about
certain hormones, their source glands and
one major effect of each on the body in
humans. Identify the correct option for the
three blanks A, B and C
Endocrine Hormone Function/Defiency
gland sympton
a) Posterior Growth Oversecretion
pituitary Hormone stimulates abnormal
(GH) growth
b) Thyroid Thyroxine Lack of iodine in
gland diet results in goitre
c) Corpus Testoste- Stimulates spermat-
luteum rone ogenesis
d) Anterior Oxytocin Stimulates uterus
pituitary contraction during
child birth
Gland Secretion Effect on body A Oestrogen Maintenance of
secondary sexual characters
Alpha cells of B Raises blood sugar
iselets of level
langerhans
Anterior C Over secretion
pituitary leads to gigantism
A B C
a) Placenta Insulin Vasopressin
b) Ovary Insulin Calcitonin
c) Placenta Glucagon Calcitonin
d) Ovary Glucagon Growth hormone
143
16. Somatostatin
a) Stimulates glucagon release while
inhibits insulin release
b) Stimulates the release of insulin and
glucagon
c) Inhibits the release of insulin and
glucagon.
d) Inhibits glucagon release while
stimulates insulin release
17. Insufficient quantities of antidiuretic
hormone in blood lead to
a) Diabetes mellitus
b) Glycosuria
c) Diabetes insipidus
d) Uremia
18. What is true about neurohypophysis?
a) Stores hormones produced by
adenohypophysis
b) Functionless in humans
c) Stores and releases neurohormones
secreted by hypothalamus
d) Secretes its own hormone
19. Which statement is correct about vitamin-D?
a) Increase Ca
+2
absorption in GUT
b) Hyposecretion in children produce
rickets
c) Increases osteoclastic activity
d) All of the above
20. Both adrenaline and cortisol are secreted
in response to stress. Which of the following
statements is also true for both of these
hormones?
a) They act to increase blood glucose
b) They are secreted by the adrenal cortex
c) Their secretion is stimulated by
adrenocorticotropin
d) They are secreted into the blood within
seconds of the onset of stress
21. If thyroid is removed from tadpole of frog, it
will
a) Die soon
b) Remains tadpole throughout life
c) Grows in to giant frog
d) Grows into dwarf frog
22. The cause of cretinism is
a) Hypothyroidism
b) Hypoparathyroidism
c) Hyperthyroidism
d) Hyperparathyroidism
23. Which hormone stimulates contraction of
gall bladder?
a) CCK-PZ b) ACTH
c) LTH d) FSH
24. If a pregnant woman having prolonged
labour pains then, to aid parturition, it is
advisable to administer a hormone that can
a) Activate the smooth muscles
b) Increase the metabolic rate
c) Tightens the pelvic ligament
d) Stimulates the ovary
25. Choose the true statement about a person
with type I (insulin dependent) diabetes
mellitus
a) There is little or no insulin secretion
b) Dietary treatment may not be sufficient
c) There is hyperglycemia
d) All of the above
26. The excess of sexcorticoides causes a
disease in females
a) Adrenal virillism
b) Aldosteronism
c) Addison’s disease
d) All of these
16. Somatostatin
a) Stimulates glucagon release while
inhibits insulin release
b) Stimulates the release of insulin and
glucagon
c) Inhibits the release of insulin and
glucagon.
d) Inhibits glucagon release while
stimulates insulin release
17. Insufficient quantities of antidiuretic
hormone in blood lead to
a) Diabetes mellitus
b) Glycosuria
c) Diabetes insipidus
d) Uremia
18. What is true about neurohypophysis?
a) Stores hormones produced by
adenohypophysis
b) Functionless in humans
c) Stores and releases neurohormones
secreted by hypothalamus
d) Secretes its own hormone
19. Which statement is correct about vitamin-D?
a) Increase Ca
+2
absorption in GUT
b) Hyposecretion in children produce
rickets
c) Increases osteoclastic activity
d) All of the above
20. Both adrenaline and cortisol are secreted
in response to stress. Which of the following
statements is also true for both of these
hormones?
a) They act to increase blood glucose
b) They are secreted by the adrenal cortex
c) Their secretion is stimulated by
adrenocorticotropin
d) They are secreted into the blood within
seconds of the onset of stress
21. If thyroid is removed from tadpole of frog, it
will
a) Die soon
b) Remains tadpole throughout life
c) Grows in to giant frog
d) Grows into dwarf frog
22. The cause of cretinism is
a) Hypothyroidism
b) Hypoparathyroidism
c) Hyperthyroidism
d) Hyperparathyroidism
23. Which hormone stimulates contraction of
gall bladder?
a) CCK-PZ b) ACTH
c) LTH d) FSH
24. If a pregnant woman having prolonged
labour pains then, to aid parturition, it is
advisable to administer a hormone that can
a) Activate the smooth muscles
b) Increase the metabolic rate
c) Tightens the pelvic ligament
d) Stimulates the ovary
25. Choose the true statement about a person
with type I (insulin dependent) diabetes
mellitus
a) There is little or no insulin secretion
b) Dietary treatment may not be sufficient
c) There is hyperglycemia
d) All of the above
26. The excess of sexcorticoides causes a
disease in females
a) Adrenal virillism
b) Aldosteronism
c) Addison’s disease
d) All of these
144
27. Correct hormonal sequence in the case of
menstruation is
a) Oestrogen, FSH, progesterone
b) Oestrogen, Progesterone, FSH
c) FSH, progesterone, oestrogen
d) FSH, oestrogen, progesterone
28. The cells that constitute the parathyroid
hormone are known as
a) Chief cells b) Oxyphil cells
c) Goblet cells d) Both (a) and (b)
29. W hich gland plays key role in
metamorphosis of frog?
a) Adrenal b) Thyroid
c) Thymus d). Pancreas
30. Source of somatostatin is the same as that
of
a) Insulin and glucagon
b) Vasopressin and oxytocin
c) Thyroxine and calcitonin
d) Somatotropin and prolactin
31. Pick out the wrong statement
a) Vasopressin is an antidiuretic hormone
b) Sex hormones are protein in nature
c) LH and ICSH are the same hormones
d) Neuro hypophysis stores neuro hormones
32. Chromophil cells are found in
a) Anterior pituitary b) Adrenal cortex
c) Thymus d) Testes
ANSWER KEYS
Simple Questions
1.a 2.c 3.c 4.a 5.d 6.a 7.b 8.a 9.a 10.d 11.c 12.a
13.c 14.a 15.b 16.b 17.b 18.a 19.c 20.c 21.c 22.c 23.c 24.b
25.a 26.c 27.a 28.c 29.d 30.d 31.a 32.b 33.b
Difficult Questions
1.d 2.b 3.b 4.a 5.c 6.c 7.b 8.c 9.a 10.d 11.b 12.b
13.b 14.a 15.d 16.c 17.c 18.c 19.d 20.a 21.b 22.a 23.a 24.a
25.d 26.a 27.d 28.a 29.a 30.b 31.a 32.b
27. Correct hormonal sequence in the case of
menstruation is
a) Oestrogen, FSH, progesterone
b) Oestrogen, Progesterone, FSH
c) FSH, progesterone, oestrogen
d) FSH, oestrogen, progesterone
28. The cells that constitute the parathyroid
hormone are known as
a) Chief cells b) Oxyphil cells
c) Goblet cells d) Both (a) and (b)
29. W hich gland plays key role in
metamorphosis of frog?
a) Adrenal b) Thyroid
c) Thymus d). Pancreas
30. Source of somatostatin is the same as that
of
a) Insulin and glucagon
b) Vasopressin and oxytocin
c) Thyroxine and calcitonin
d) Somatotropin and prolactin
31. Pick out the wrong statement
a) Vasopressin is an antidiuretic hormone
b) Sex hormones are protein in nature
c) LH and ICSH are the same hormones
d) Neuro hypophysis stores neuro hormones
32. Chromophil cells are found in
a) Anterior pituitary b) Adrenal cortex
c) Thymus d) Testes
ANSWER KEYS
Simple Questions
1.a 2.c 3.c 4.a 5.d 6.a 7.b 8.a 9.a 10.d 11.c 12.a
13.c 14.a 15.b 16.b 17.b 18.a 19.c 20.c 21.c 22.c 23.c 24.b
25.a 26.c 27.a 28.c 29.d 30.d 31.a 32.b 33.b
Difficult Questions
1.d 2.b 3.b 4.a 5.c 6.c 7.b 8.c 9.a 10.d 11.b 12.b
13.b 14.a 15.d 16.c 17.c 18.c 19.d 20.a 21.b 22.a 23.a 24.a
25.d 26.a 27.d 28.a 29.a 30.b 31.a 32.b
145
1. A tumour in the adrenal zona glomerulosa
can cause hyper secretion of hormones
produced in that region, which of the
following might you expect to find in a patient
with such a tumour
a) Increased blood sodium levels
b) Increased blood glucose levels
c) Decreased blood calcium levels
d) Increased dehydration
2. Which part of brain is supposed to be
damaged if in an accident, a person lost
control of water balance, hunger and body
temperature?
a) Cerebellum
b) Hypothalamus
c) Medula oblongata
d) Corpora quadrigemina
3. Thyrotropin – releasing factor (TRF) is
produced by
a) Cerebrum b) Optic lobe
c) Cerebellum d) Hypothalamus
4. Which of the following is an accumulation
and release centre of neurohormones?
a) Anterior pituitary lobe
b) Neurohypophysis
c) Pars intermedia
d) Hypothalamus
DPP - 5
5. Blood pressure is controlled by
a) Thyroid gland
b) Thymus gland
c) Adrenal gland
d) Parathyroid gland
6. Which of the following two hormones have
antagonistic effects?
a) Parathormone and calcitonin
b) FSH and LH
c) Oestrogen and progesterone
d) ADH and melatonin
7. Norepinephrine leads to increase in
a) Blood pressure
b) Urine production
c) Cellular respiration
d) Release of epinephrine
8. The diabetes mellitus is caused by
a) Hyper secretion of insulin
b) Hyposecretion of insulin
c) Hyposecretion of ADH
d) Hyper secretion of ADH
9. In parasympathetic nervous system, which
of the following is released?
a) Epinephrine b) Norepinephrine
c) Serotonin d) Acetylcholine
10. “Cushing” disease is related with
a) Thyroid b) Parathyroid
c) Adrenal d) Gonads
1. A tumour in the adrenal zona glomerulosa
can cause hyper secretion of hormones
produced in that region, which of the
following might you expect to find in a patient
with such a tumour
a) Increased blood sodium levels
b) Increased blood glucose levels
c) Decreased blood calcium levels
d) Increased dehydration
2. Which part of brain is supposed to be
damaged if in an accident, a person lost
control of water balance, hunger and body
temperature?
a) Cerebellum
b) Hypothalamus
c) Medula oblongata
d) Corpora quadrigemina
3. Thyrotropin – releasing factor (TRF) is
produced by
a) Cerebrum b) Optic lobe
c) Cerebellum d) Hypothalamus
4. Which of the following is an accumulation
and release centre of neurohormones?
a) Anterior pituitary lobe
b) Neurohypophysis
c) Pars intermedia
d) Hypothalamus
DPP - 5
5. Blood pressure is controlled by
a) Thyroid gland
b) Thymus gland
c) Adrenal gland
d) Parathyroid gland
6. Which of the following two hormones have
antagonistic effects?
a) Parathormone and calcitonin
b) FSH and LH
c) Oestrogen and progesterone
d) ADH and melatonin
7. Norepinephrine leads to increase in
a) Blood pressure
b) Urine production
c) Cellular respiration
d) Release of epinephrine
8. The diabetes mellitus is caused by
a) Hyper secretion of insulin
b) Hyposecretion of insulin
c) Hyposecretion of ADH
d) Hyper secretion of ADH
9. In parasympathetic nervous system, which
of the following is released?
a) Epinephrine b) Norepinephrine
c) Serotonin d) Acetylcholine
10. “Cushing” disease is related with
a) Thyroid b) Parathyroid
c) Adrenal d) Gonads
Download
Download Slideshow Get the original presentation fileQuick Actions
Statistics
- Views 225
- Slides 145
- Age 597 days
Related Slideshows
11
TLE-9-Prepare-Salad-and-Dressing.pptxkkk
MaAngelicaCanceran
32 views
12
LESSON 1 ABOUT MEDIA AND INFORMATION.pptx
JojitGueta
27 views
60
GRADE-8-AQUACULTURE-WEEKQ1.pdfdfawgwyrsewru
MaAngelicaCanceran
42 views
26
Feelings PP Game FOR CHILDREN IN ELEMENTARY SCHOOL.pptx
KaistaGlow
41 views
![Jeopardy_Figures_of_Speech_Template.pptx [Autosaved].pptx](https://slidepub.com/thumb/5828/284015828.jpg)
54
Jeopardy_Figures_of_Speech_Template.pptx [Autosaved].pptx
acecamero20
25 views
7
Jeopardy_Figures_of_Speech.pptxvdsvdsvsdvsd
acecamero20
25 views