1. Introduction to Nervous system.pdf hhhhs

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1. Nervous system
By Dr. Ann Mwangi
Department of Human Anatomy
JKUAT

2. Nervous System
Outline
1. Definition of N/S
2. Functions
3. Divisions
4. Cellular Components of N/S

3. Definition
•Nervous system-Is a rapid communication system of the body,
carrying electrochemical impulses (coded signals from a stimuli).
•Is a very important in maintenance of body homeostasis (body
balance-equilibrium)
•Nervous system works with sensory receptors(protein molecules)
inside a target cell or on its surface that receives chemical signals-to
provide information about changesin both internal and external
environment

4. Functions of N/S
Primary function
Co-ordination–of voluntary & involuntary actions of body in relation to
the internal and external stimulus.
Secondary functions
1.Sensation -In internal & external environment
2.Integration -of sensory Information (brain and spinal cord)
3.Regulation /control of peripheral structures & systems (mm
contraction & movements)
4.Higher functions –like memory, drives, emotions and learning
(skilled/unskilled)

5. NS works through a Reflex arc

6. Classification/Divisions of Nervous System
•NS has 2 divisions
1.Central nervous system (CNS):
It is composed of the brain and spinal cord (approx. 95% body's neural tissue)
Performs integration & co-ordination of nervous activity
Higher functions like learning and memory
2. Peripheral nervous system (PNS)
Composed of all of neural tissue outside CNS
Links CNS with all of body tissues & outside world

7. NERVOUS SYSTEM
CNS PNS
BRAIN SPINAL CORD SOMATIC NS ANS NS
12 PAIRED
CRANIAL
NERVES
31 P OF SPINAL
NERVES
SNS PNS ENS

8. Central Nervous System
1. The Brain
Thebrainhas three mainparts
•The cerebrum.
•The cerebellum
•The brainstem.
•Cerebrum: is the largestpartof
thebrainand is composed of right and
lefthemispheres separated by a deep
mid-line fissure.
•Cerebellum: is located under the
cerebrum.
•Brainstem: Acts as a relay center
connecting the cerebrum and
cerebellum to the spinal cord.
•It is composed of the midbrain, the
ponsand the medulla oblongata.

11. 2. Thespinal cord
•Is a long, thin, tubular structure
made up of nervous tissue,
which extends from the medulla
oblongata in the brainstem to
thelumbarregion of the vertebral
column.

12. •Spinal cord is responsible for;
(i)It serves as a conduit (channel) for conveying signals between the
brain and the rest of the body, acting asa point at which the
neurons synapse
(ii)controls simple musculoskeletal reflexes without input from the
brain.

15. Peripheral Nervous System
Somatic Nervous System
12 Pairs of Cranial nerves
•The twelvecranial nervesare a group of nerves that originate in the brain
and provide motor and sensory functions to the head and neck structurers
•They arise directly from the brain and exitfrom the foramina and fissures
of the cranium
•They include;
1. CN (I)-Olfactory-Sensory
2. CN(II)-Optic-Sensory
3. CN(III)-Oculomotor-Motor
4. CN(IV)-Trochlea-Motor
5. CN(V)-Trigeminal--Mixed

16. 6. CN(VI)-Abducens-Motor
7. CN(VII)-Facial-Mixed
8. CN(VIII)-Vestibulo-cochlea-Sensory
9. CN(IX)-Grosso-pharyngeal-Mixed
10. CN(X)-Vagus-Mixed
11. CN(VI)-Accessory-Motor
12. CN(XII)-Hypoglossal -Motor

21. 31 Pairs of spinal nerves
They include;
•8 cervical,
•12 thoracic,
•5 lumbar,
•5 sacral, and
•1 coccygeal.
•Each pair connects the spinal cord with a specific region of the body.

23. Coronal section of spinal cord

24. Theautonomic nervous system
•Is a controlsystemthat acts unconsciously/involuntarily to regulate
bodily functions such as the heart rate, digestion, respiratory rate,
pupillary response, urination, sexual arousal etc.
1. Sympathetic NS-directsthe body's rapid involuntary response to
dangerous or stressful situations (control of the fight-or-flight
response).
•Act with hormones that boosts the body's alertness and heart rate,
sending extra blood to the muscles.
2. Parasympathetics NS-It functions to conserve the body's natural
activity and relaxes the individual once an emergency has passed (for
return to normancy)

25. Organ Sympathetic System Parasympathetic System
Eye
Tear glands
Salivary glands
Lungs
Heart
Gut
Liver
Bladder
Dilates pupil
No effect
Inhibits saliva production
Dilates bronchi
Speeds up heart rate
Inhibits peristalsis
Stimulates glucose production
Inhibits urination
Constricts pupil
Stimulates tear secretion
Stimulates saliva production
Constricts bronchi
Slows down heart rate
Stimulates peristalsis
Stimulates bile production
Stimulates urination

27. 3. Theenteric nervous system(ENS)
•Is a large division of the peripheralnervous
system(PNS) that can control gastrointestinal
behaviour independently of centralnervous
system(CNS) input.
•It controls all digestive processes, namely
motility, ion transport associated with
secretion and absorptionetc. It is comprised
of;
a.Themyenteric plexus/Auerbach's plexusis
located between the longitudinal and
circular layers of muscles (for peristalsis)
b.Thesub-mucousplexus/Meissner'splexus,
as its name implies, is buried in the
submucosa (for local churning of food).

28. Cellular components of the nervous system
•The nervous system has two cellular components:-
1.The neurons-These are the structural and functional units of the nervous
system.
2.The neuroglial cells-They are involved in support and protection within the
nervous system
Terms in the nervous system
Neurons/Nerve cells -Are the fundamental units of the nervous system,
responsible for receiving sensory input from the external world, sends motor
commands to our muscles, transforms and relay the electrical signals at every
step in between
Nerve-bundle of neuronal fibers in the PNS
Tract-collection of nerves that connects regions of CNS
Ganglion-bundle of nerve cell bodies outside of CNS
Nucleus-bundle of nerve cell bodies within CNS

29. 1.The neurons:
•These are the structural and functional units of the nervous
system.
•They are specialised cells that transmit chemical & electrical
signals to facilitate communication between the brain and
the body
Characteristics of neurons:-
a)Excitabilityi.e. ability to be activated by a stimulus.
b)Conductivityi.e. ability to propagate the impulse
The functional domains of neurons:-
a)Receptive domain:-comprises of the dendritic system
b)Integration domain:-is the trophiccentre and consists
of the cell body/soma
c)Transmission domain:-is made of the axon

31. Parts of a neuron
1. Cell body/soma-contains the
nucleusand other organellesthat
guides cellular functions
2. Dendrites-are specialized extensions
that act as receptorprocesses
(convert signals into small electrical
impulses and transmit them in the
direction of the cell body.)
3. Axon-A structure that transmits
impulses
AWAY from the cell body
•Can be several feet long

32. 4. Axon hillock-Is the initial part located near
the cell body where nerve impulses are
summed up.
•If this sum exceeds the limiting threshold,
then there will beanaction potential.
•This results in the transmission of the
generated electrical signal through the axon
away from the neuronal cell body.
5. Myelin sheath -is an insulating layer, or
sheath that surrounds/ wrapped around the
axon (myelination).
•It allows electrical impulses to be transmitted
quickly and efficiently along the nerve cells.
>>In periphery, myelin is produced by
Schwann cells
>>In CNS, it is produced by oligodendrocytes

33. 6. Nodes of ranvier-Periodic gaps in the
insulating sheath (myelin) on the axon of
certain neurons that serves to facilitate the
rapid conduction of nerve impulses.
7.Terminal boutons-The specialized
presynapticterminal inflatedends of an
axon.
•They release the neurotransmitter
substances

34. Types of nerve
conduction
i)Saltatory conduction -Nerve
impulsepropagates by jumping from
one node of Ranvier to the next.
ii)This makes the process ofnerve
impulsefaster as thenerve
impulsedoes not travel the entire
length of the axon .

35. ii) Continuous conduction-occurs in
unmyelinated axons.
•This process involves the sequential opening of
voltage gated Na+ and K+ channels located within
the axon membrane along the entire length of the
axon to propagate an impulse

36. Differences between dendrites and axons
Dendrites
•Bring information to the cell body
•Rough surface (dendritic spines)
•Usually many dendrites per cell
•No myelin insulation
•Branch near the cell body
Axons
•Take information away from the cell body
•Smooth Surface
•Generally only 1 axon per cell
•Can have myelin
•Branch further from the cell body

37. Histological features of neurons
i) Nucleus: Is large and rounded with large central neucleolus that
reflect high degree of transcriptional activity
ii) Abundant rough endoplasmic reticulum:which synthesize the necessary
proteins.
iii) Well developed Golgi apparatus:-for production of secretory vesicles and lipids
iv) Large number of mitochondriathat supply the required energy
v) Numerous lysosomesbecause of a high turn over of the cell membrane and
other cell components
vi) The cytoskeleton:-Is highly organized to maintain the unique shape of these cells and
particularly their long axons which may be up to one meter.
•Neuro-filamentsand intermediate filaments-act as internal scaffold to maintain the
shape of the axon and the cell body.
•There are also organized pattern of microtubulesfor transportationof substances and
organelles up and down the axons

38. Types/classification of neurons
1.Based on direction of impulse
(a)Afferents
•Conduct impulses from sensory receptors to
CNS)
•They are organize in to 3 groups/orders
i) 1
st
order neurons (transmits impulses to
the spinal cord)
ii) 2
nd
order neurons (transmits impulses
from the spinal cord to the thalamus)
iii) 3
rd
order neurons (transmits impulses
from the thalamus to the sensory region of
cerebral cortex)

39. b)Efferent nerves
•Conduct impulses from CNS to effector the
organ.
• They are organized into two groups
i)Upper motor neurons-Carry information
down to the lower motor neuron (do not
leave the CNS) and synapse with lower
motor neurons).
ii) Lower motor neurons neurons-Carry
information down from CNS to the
target organ

40. c) Interneurons
•They located entirely within CNS, they
integrates functions
in CNS.
•Connects sensory & motor neurons.
-The information involving this
nerves is conducted very fast, is from a
noxious stimuli and may cause nerve
damage

41. 2. Classification of neurons
based on types of modalities
A.Sensory neurons
•Carry sensory information
from the receptor to the
brain or spinal cord
•Have long dendrites and a
short axon

42. B. Motor nerves
•Carry motor information from
the integration center to the
effector organ
•Have short dendrites and a
long axon

43. 3. Classification of neurons
based on shape/morphology
a) Unipolar neurons
•Have single neurite on one end of
cell body that function as both dendrite
and axon.
•Only found in invertebrates and not
humans
•Are found in the cerebral cortex and
spinal cord

44. b) Pseudo unipolar
-Have one process that later divides
into a dendrite and an axon
-Forms sensory nerves

45. c) Bipolar neurons
-Cell body with processes at both ends (an
axon and a dendrite)
-Forms inter-neurons

46. d) Multipolar neurons
•Most common in the CNS
i) Golgi type I neurons:-have
long axons like one meter
long (projection neuron)-
most motor nerves

47. ii) Golgi type II neurons:
are star shaped
commonly found in the
cortices