Nervous system ( anatomy and physiology)

the topic contain function of nervous system, classification of nervous system, neurons anatomy, structural classification of neurons, functional classification of neurons, nerve impulse

1. The Nervous System
(Anatomy and Physiology)
Ravish Yadav

2. •Most complex systeme in body –regulate 1oos of activities
simultaneously.
•It is the source of intelligence, consciousness, creativity & allows us to
communicate & experience emotions.
•It control all voluntary actions & non-voluntary up to some extent like
breathing.
•The activity of nervous system is performed by nerve cells called
“Neurons”.

3. •The nervous system coordinates all body functions,
enabling a person to adapt to changes in internal and
external environment
•The nervous system is composed mainly of the nerve
cells (neurons) and supporting cells (neuroglia)
•The branch of science that deals with the normal functions & disorders
of nervous system called “Neurology”

4. Functions of the Nervous System
Sensory input/function –gathering information
To monitor changes occurring inside and outside the body
like increasing blood acidity or external stimuli etc.
Than sensory information is carried to brain & spinal cord
through cranial & spinal nerves.
Integration-To process and interpret sensory input
and decide if action is needed.
Motor output/function:
A response to stimuli
Activates muscles or glands

5. Classification of the Nervous System

6. Nervous System Histology
Neurons= nerve cells
This is the basic conducting cell of
the nervous system.
Cells specialized to transmit
electrochemical messages.
Make specific contects with other
neurons called “synapes” across
which signals are passed.

7. •There are about 100 billion neurons in the human brain.
•These neurons have many shapes and come in many sizes.
•Their job is to allow you to think and behave.
•For example, solving a math problem in your head and raising
your hand in class to answer the teacher’s question are both
activities that are controlled and coordinated by your brain
through the behavior of neurons.

8. Neuron Anatomy
(1)Cell body (soma): contains nucleus, ribosomes,
mitochondria & ER (specialized rough ER).
All the neuronal proteins etc. components are
synthesized here.
(2)Dendrites–these are thinner, fibrous & highly
branched projections extending outwards from the cell
body.
Each cell contain many Dendrites.
These are input portions of a neuron & receive signals
from organs or from the axon of the other neuron.
The signals are converted to electrical impulses &
transmitted to the cell body.

9. •(3)Axon–each cell contain 1 axon that is a thin,
long, cylindrical fibre that conduct nerve impulses
away from the cell body.
•Major output portion.
•Axon may be metre or more in length & diametre
can be vary from micrometre to millimetre.
•The membrane of axon called “axolemma”
contain axoplasm.
•Neurons are surrounded by sheath of fatty
materials called “myelin sheath ”

10. myelin sheath & non-myelinated parts if axon
again covered by “Nuerolemma”
myelinated sheath conduct electrical impulses
faster than non-myelinated axons.
Junction of cell body & axon called “axon
hillock” so action potential generated at this
junction & travel to small branches of axon
called “axon terminals”.

11. (4) Axon terminals:
•Axon undergo branching, each axon branch ending called “Axon
terminals”.
•These are responsible for the transmitting signals from one neuron to
next neuron or at the muscle cell at the neuromuscular junction.

13. Characteristics of neurons:
Irritability conductivity
Ability to
intiate/generate nerve
impulse. Stimulated
by 2 stimulations
Transmission of
impulse from one part
to another
internal external
Like change in concn of
Co2 in blood
Like touch, light,
sound etc

14. Structural Classification of Neurons
•Based on the # of processes that
extend from cell body.
•Pseudounipolar:
•Short single process that
branches like a T.
•Sensory neurons.
•Bipolar neurons:
•Have 2 processes.
•Retina of the eye.
•Multipolar:
•Have several dendrites and 1
axon.
•Motor neuron.

15. Functional Classification of Neurons
(1)Sensory neurons
Carry nerve impulses from a receptor to the CNS
Have longdendrites and shortaxons
(2)Motor neurons
Carry nerve impulses from the CNS to an effector(ex.
muscle or gland)
Have shortdendrites and longaxons
(3)Interneurons
Found completely within the CNS
Provide a link within the CNS between sensoryneurons
and motorneurons
Have short dendrites and long or short axons

16. Neuron Classification
Figure 7.6

17. The neuroglia
•The supporting cells
•They supply nutrients to the neurons and help
maintain the electrical potential
•They also form part of the blood-brain barrier
•They are made up of macroglia, microglia and
ependymal cells

18. •Oligodendrocytes produce myelin sheath in the CN
•Scwhann cells or lemmocytes produce myelin
sheath in the peripheral NS

19. Electrochemical Nerve Impulses
Dendrite depolarization
–a stimulus depolarizes
the dendrite’s membrane
Sodium (Na
+
) flows
inside the membrane
with the help of Na+
pumps
This exchange of ions
initiates an (+) action
potentialin the neuron

20. The Action Potential
If the action potential (nerve impulse)
starts, it is propagated to the end of the
axon
Potassium (K+) ions rush out of the
neuron after sodium ions rush in, which
repolarizesthe membrane
The sodium-potassium pump restores
the original configuration -which is
resting potential (-)
*** This action requires ATP ***

22. Continuation of the Nerve
Impulse between Neurons
Impulses are able to cross the synapse
to another neuron
Neurotransmitter is released from a
neuron’s axon terminal
The dendrite of the next neuron has
receptors that are stimulated by the
neurotransmitter
An action potential is started in the dendrite

23. How Neurons Communicate at
Synapses
Figure 7.10

24. Neurotransmission
•also calledsynaptic transmission, is the process by which signaling molecules
calledneurotransmittersare released by aneuron(the presynaptic neuron), and
bind to and activate thereceptorsof another neuron (the postsynaptic neuron).
•It is essential for the process of communication between two neurons

25. Stages in neurotransmission at the synapse
(1)Synthesis of the neurotransmitter. This can take place in thecell body, in the
axon, or in theaxon terminal.
(2)Storage of the neurotransmitter in storage granules or vesicles in the axon
terminal.
(3)Calcium enters the axon terminal during an action potential, causing
exocytosis/releaseof the neurotransmitter into the synaptic cleft.
(4)After its release, the transmitter binds to and activates a receptor in the
postsynaptic membrane.
(5)Deactivation of the neurotransmitter. The neurotransmitter is either
destroyed enzymatically, or taken back into the terminal from which it
came, where it can be reused, or degraded and removed

27. •A presynaptic neuron converts an electrical signal (nerve impulse) into a
chemical signal (neurotransmitter release).
•The postsynaptic neuron then converts the chemical signal back into an
electrical signal.

28. The Reflex Arc
Reflex–rapid, predictable, and
involuntary responses to stimuli
Reflex arc –direct route from a sensory
neuron, to an interneuron, to an effector

29. •Areflex arcis aneural pathwaythat controls a reflex action. In higher
animals, most sensory neurons do not pass directly into thebrain, but
synapse in thespinal cord.
•This characteristic allows reflex actions to occur relatively quickly by
activating spinal motor neurons without the delay of routing signals
through the brain, although the brain will receive sensory input while
the reflex is carried out.
•Analysis of the signal takes place after action has been taken

31. Regions of the Brain
Cerebral
hemispheres
Diencephalon
Brain stem
Cerebellum

32. Cerebral Hemispheres (Cerebrum)
Paired (left and
right) superior
parts of the brain
Include more
than half of the
brain mass
The surface is
made of ridges
(gyri) and
grooves (sulci)

33. Specialized Area of the Cerebrum

34. Specialized Areas of the Cerebrum

35. Diencephalon
Sits on top of the brain stem
Enclosed by the cerebral hemispheres
Three parts:
Thalamus
Hypothalamus
Epithalamus

36. Brain Stem
Attaches to the spinal cord
Parts of the brain stem:
Midbrain
Pons
Medulla
oblongata

37. Cerebellum
Two hemispheres
with convoluted
surfaces
Provides involuntary
coordination of body
movements
“Arbor vitae” design
of white & grey
matter

38. Extends from the
medulla oblongata to
the region of T12
Below T12 is the cauda
equina (a collection of
spinal nerves)
Carries sensory and
motor information
Figure 7.18
Spinal Cord Anatomy

39. Cranial Nerves
12 pairs of nerves
that mostly serve the
head and neck
Numbered in order,
front to back
Most are mixed
nerves, but three
are sensory only

40. Cranial Nerves
IOlfactorynerve –sensory for smell
IIOpticnerve –sensory for vision
IIIOculomotornerve –motor fibers to eye
muscles
IVTrochlear–motor fiber to eye muscles
VTrigeminalnerve –sensory for the face;
motor fibers to chewing muscles
VIAbducensnerve –motor fibers to
eye muscles

41. Cranial Nerves
VIIFacialnerve –sensory for taste; motor
fibers to the face
VIIIVestibulocochlearnerve –
sensory for balance and hearing
IXGlossopharyngealnerve –sensory for taste;
motor fibers to the pharynx
XVagusnerves –sensory and motor fibers for
pharynx, larynx, and viscera
XIAccessorynerve –motor fibers to neck and
upper back
XIIHypoglossalnerve –motor fibers to tongue

42. Spinal Nerves to know:
UlnarNerve –Motor &
Sensory, “the funny bone”
RadialNerve –Motor &
Sensory
MedianNerve –Motor &
Sensory
The Brachial Plexus (Arm)

43. The LumbrosacralPlexus (Leg)
Spinal Nerves:
Sciatic–M,S
Femoral–M,S
Obturator–M,S
Tibial–M,S
Common Fibular –M,S