UNIT – 11

NERVOUS SYSTEM
SYSTEM
11.1 Introduction:- Nerve, neuroglia, synapse nerve transmission
11.2 Types of nerves
11.3 Mechanism of stimuli transmission
11.4 The central nervous system:- Covering membrane(meninges),
Cerebrum, Mid brain, Cerebellum, Brain stem, Ventricles,
Spinal cord
11.5 The peripheral nervous system:- Spinal nerve, cranial nerve,
Autonomic nervous system
11.6 Neurones
 Mechanism of stimuli transmitted in the nervous system- Reflex
action
 CNS- Brain and spinal cord

 PNS- Spinal cord and cranial nerves

 ANS-Sympathetic and parasympathetic system

INTRODUCTION
 The nervous system is the system of communication between the
various parts of the body.
 It is the mechanism by which sensation of all kinds are received
from the environment, from the tissues and ongans of the body
itself.
 It is the system by which action are also carried out by the
sending of impulse to other parts of the nervous system and
organs of the body.
 Humans, like all living organisms, can respond to their
environment. Humans have two complimentary control systems
to do this: the nervous system and the endocrine (hormonal)
system. The human nervous system controls everything from
breathing and producing digestive enzymes, to memory and
intelligence.
THIS NERVOUS SYSTEM CAN BE
DIVIDED INTO TWO MAIN PARTS:
1. The central nervous system (CNS) that consists of :
a) The brains
b) Spinal cord

2). Three peripheral nervous system (PNS) that consists of

:
c) Spinal nerve – 31 pairs
d) Cranial nerves – 12 pairs
e) Autonomic nervous system (ANS)
i) Sympathetic and
ii) Parasympathetic nerves
 Nervous
system

Central Peripheral
nervous nervous
system system
(CNS) (PNS)

Spinal Cranial Autonomi

Brain Spinal nerves c nervous
cord nerves
(12pairs) system
(31 pairs)
(ANS)
FUNCTION
 Registration of information
 Regulation of body function.

 Transportation of sensations.

 Storage of information

 Formation of thoughts through learning and gaining

experience.
THE NERVE CELL (NEURONS)
 The nervous system composed of nerve cells,
or neurons. which are structural and functional unit of
nervous system.
 Neurons are supported by a special kinds of connective
tissue called neuroglia.
 The basic properties of neuron are irritability or
excitability and conductivity.
 The neurone can be divided into three parts:
I. A cell body (Soma)
II. An axon

III. Dendrites
 Cell body:- cell body forms the grey matter of nervous system
and found at the periphery of the brain & in the central of spinal
cord. Group of cell bodies are called nuclei in CNS and ganglia
in PNS.
The cell body contains protoplasm and centrally placed nucleus.
The protoplasm of cell has large granules called Nissil granules
or bodies.
 Axone:- Each nerve cell has only one axone , which begins at a
tapered area of the cell body, the axon hillock. It carries
impulses away from the cell body . The membrane of axon is
called axalemma. The axon may be myelinated or non
myelinated usually large axon.
The axon has a uniform diameter.
In additional to this difference in structure , There is a fundamental
functional difference between dendrites and axon.
The axon is sometimes about 100 cm long.
Function of myelin sheath are:-
 To prevent axon from pressure & injury.

 To act as electrical insulator so that flow of impulses goes

unrestricted along the nerves.
 Dendrites:- Dendrites are the many short processes that
receive and carry incoming impulses towards call
bodies . In motor neurons dendrites from part of synapes
and in sensory neurones they form the sensory receptors
that respond to specific stimuli.
  There are several differences between axons and dendrites:

Axons Dendrites

Take information away from the cell Bring information to the cell body
body
Smooth Surface Rough Surface (dendritic spines)

Generally only 1 axon per cell Usually many dendrites per cell

No ribosomes Have ribosomes

Can have myelin No myelin insulation

Branch further from the cell body Branch near the cell body
Neurons are similar to other cells in the body because:
 Neurons are surrounded by a cell membrane.
 Neurons have a nucleus that contains genes.
 Neurons contain cytoplasm, mitochondria and other organelles.
 Neurons carry out basic cellular processes such as protein synthesis
and energy production.

Neurons differ from other cells in the body because:

 Neurons have specialised extensions called dendrites and axons.
Dendrites bring information to the cell body and axons take
information away from the cell body.
 Neurons communicate with each other through an electrochemical
process.
 Neurons contain some specialized structures (for example,
synapses) and chemicals (for example, neurotransmitters).
HUMANS HAVE THREE TYPES OF NEURONES

 Sensory neurons have long axons and transmit nerve impulses

from sensory receptors all over the body to the central nervous
system.
 Motor neurons also have long axons and transmit nerve
impulses from the central nervous system to effectors (muscles
and glands) all over the body.
 Inter neurons (also called connector neurons or relay neurons)
are usually much smaller cells, with many interconnections.
MOTOR NEURON:
  Efferent Neuron – Moving toward a central organ or point
 Relays messages from the brain or spinal cord to the muscles
and organs.
SENSORY NEURON:
 Afferent Neuron – Moving away from a central organ or point
 Relays messages from receptors to the brain or spinal cord.
INTERNEURON (RELAY NEURON):
 Relays message from sensory neuron to motor neuron
 Make up the brain and spinal cord
  Sensory neuron Interneuron Motor Neuron

Short dendrites
Long dendrites Short dendrites
Length of Fibers and short or long
and short axon and long axons
anxon

Cell body and

Dendrites and the
dendrite are
cell body are
outside of the
Entirely within the located in the
Location spinal cord; the
spinal cord or CNS spinal cord; the
cell body is located
axon is outside of
in a dorsal root
the spinal cord
ganglion

Interconnect the
Conduct impulse
Conduct impulse sensory neuron
Function to an effector
to the spinal cord with appropriate
(muscle or gland)
motor neuron
THE REFLEX ARC   
 The three types of neurons are arranged in circuits and
networks, the simplest of which is the reflex arc.
 In a simple reflex arc, such as the knee jerk, a stimulus is
detected by a receptor cell, which synapses with a sensory
neuron. The sensory neuron carries the impulse from site of the
stimulus to the central nervous system (the brain or spinal
cord), where it synapses with an inter neuron. The inter neuron
synapses with a motor neuron, which carries the nerve impulse
out to an effectors, such as a muscle, which responds by
contracting.
THE NERVES IMPULSES (ACTION
POTENTIAL)
 Action potentials are rapidly developing electrochemical changes
occurring in cell membranes of excitable cells. The transmission of
impulses , is due to movement of ions across the nerves cell membrane.
 In resting state ,the nerve cell membrane is polarized due to differences
in the concentration of ions across the plasma membrane which is called
resting membrane potential(The RMP of a neurone is about
-70mV(mV=millivolt) this means that the inside of the neurone is
-70mV less than the outside. At rest, there are relatively more sodium
ions outside the neurone and more potassium ions inside the neurone ) .
 Or, The potential difference between the two sides of the membrane of a
nerve cell when the cell is not conducting impulses.
 At rest the charge on outside is positive & inside is negative . The ions
involved are:-
 Sodium (Na+), Main extracellular cation
 Potassium(K+) ,Main intracellular cation.
 In resting state there is continual tendency for these ion to diffuse
along their concentration gradients ie K+ outsides & Na+ into
cells through the ion leaky channels.
 Now, when stimulated ,the permeability of the nerve cell
membrane to these ions changes . It produces an initial opening
of voltage- gated sodium channel causing Na+ to flood inside the
cell from extracellular fluid leading depolarization, creating a
nerve impulses or action potential followed by opening of
voltage-gated potassium channel leading to repolarization .
 Almost immediately following the entry of sodium, k+ floods out
of the neuron & the movement of these ions returns the
membrane potential to its resting state. This is called refractory
period during which restimulation is not possible.
 As the neuron returns to its original resting state, the action of
sodium – potassium pump (sodium – potassium ATPs ases) expel
Na+ from the cell in exchange for K+.
 In myelinated neurons ,the insulating properties of the myelin
sheath prevent the movement of ions. Therefore electrical
charges across the membrane occurs only at the nodes of
Ranvier. When an impulses occure at one node, depolarization
passes along the myelin sheath to the next node so that the flow
of current appears to leap from one node to the next. This is
called saltatory conduction(Quick propropagation of the action
potential along a myelinated axon owing to voltage gated Na+
channela being present only at the node of ranvier ).
 The speed of conduction depends on the diameter of neuron;
larger the diameter , faster the conduction. So , mylinated fibers
conduct impulses faster than unmyelinated fibers because
saltatory conduction is faster than simple propagation.
 NEUROGLLA
 Neuroglia is the nervous system cell. They surround the neuron.
These cells consists of specialized connective tissues. They perform
a variety of supportive functions to impulses conduction .
 Neuroglia produces the myelin that insulates(protect from heat, cold
or noice by surrounding with insulating material) and functionally
isolates neurons.
 Varieties of neuroglia are:-

a. Ependymal cells:- are the epithelial cells that line the neural canal
and brain ventricles.
b. Astrocytes:- Are present around the blood vessels in the brain
parenchyma.
c. Oligodendroglia:- Produce myelin in the CNS.

d. Microglia :- is part of the mononuclear phagocyte to system in

brain.
e. Satellite cells:- Are present in PNS ganglia.
SYNAPES
 Synapse is the functional region between two neurons, where
information from one neuron is transmitted or relayed (hand
over) to another neuron ,but there is no protoplasmic
connection between the two neurons. So there is space (gap)
between the two neurons called synaptic cleft.
 A synapse = presynaptic knob + synaptic cleft + post synaptic
membrane.
 Neural signals propagate along an axon in the form of
electrochemical waves called action potentials, which produce
cell-to-cell signals at points where axon terminals make 
synaptic contact with other cells.
 Synapses may be electrical or chemical. Electrical synapses
 make direct electrical connections between neurons(impulses as
heart muscles), but chemical synapses are much more common,
and much more diverse in function. At a chemical synapse, the
cell that sends signals is called presynaptic, and the cell that
receives signals is called postsynaptic. Both the presynaptic and
postsynaptic areas are full of molecular machinery that carries
out the signalling process. The presynaptic area contains large
numbers of tiny spherical vessels called synaptic vesicles,
packed with neurotransmitter chemicals. When the presynaptic
terminal is electrically stimulated, an carray of molecules
embedded in the membrane are activated, and cause the contents
of the vesicles to be released into the narrow space between the
presynaptic and postsynaptic membranes, called the 
synaptic cleft.
 The neurotransmitter then binds to receptors embedded in the
postsynaptic membrane, causing them to enter an activated
state. Depending on the type of receptor, the resulting effect
on the postsynaptic cell may be excitatory, inhibitory, or
modulatory in more complex ways. For example, release of
the neurotransmitter acetylcholine at a synaptic contact
between a motor neuron and a muscle cell induces rapid
contraction of the muscle cell. The entire synaptic
transmission process takes only a fraction of a millisecond,
although the effects on the postsynaptic cell may last much
longer
 TYPES OF SYNAPSE
 There are three types of synapses:-
a. Axo – dendritic:- Axone is terminating on a dendrone of
another neuron
b. Axo- somatic :- Axone is terminating on the nerve cell body
(Soma) of another neuron
c. Axo axonic , where an axone is terminating on another axon.
 Neurotransmitter
Acetylcholine (ACH)
Motor Movement and.
Dopamine
Motor movement and Alertness.
Endorphins
Pain Control
Serotonin
Mood Control
NERVES TERMINATION
 Afferent (Sensory) termination:- Input of nerve impulses into
the central nervous system results from stimulation of a wide
variety of sensory receptors which may be special sense
receptors, cutaneous receptor, proprioceptors and
enteroceptors. For example, in the skin , the sensory nerve lose
their myelin sheath and neurilemma(a memberanous sheath
around a nerve fiber) and divide into small branches known as
sensory receptors. The cutaneous receptors are stimulated by
touch, pain , temperature. Then these impulses are transmitted
to the brain where sensation is perceived.
 Efferent (motor)termination:- Efferent (motor)nerve carry out
the impulses from the brain to the various part of the body.
as the axon supplying a skeletal muscle fiber approaches its
termination , it loses its myelin sheath and divided into a number
of terminal buttons or end feet . The end feet fit into depression
in the motor end plate, the thickened portion of the muscle
membrane of the junction. There is a tiny space between the
nerve ending and the thickened muscle membrane is
comparable to the synaptic cleft at synapses. The whole
structure is known as the neuromuscular junction. Only nerve
fiber end on each end plate.
THE CENTRAL NERVOUS SYSTEM
 The central nervous system consists of brain and spinal
cord.
THE BRAIN AND ITS COVERINGS
The brain lies in the cranial cavity . An average weight is
about 1.5 kg.
The brain consists of the following important parts:-
 Covering membranes

 Cerebrum

 Brain stem

 Cerebellum

 Ventricles
 A) COVERING MEMBRANES
 The brain and spinal cord are very important but delicated
organs. They are protected by the following coverings.
i. The bony covering of the cranium and vertebras
ii. Three membranous covering called meninges.

The meninges:- Brain and spinal cord are completely surrounded

by a membranous sheet called meninges. It has three layers:-
iii. Dura mater

iv. Archnoid mater

v. Pia mater
 Dura mater:- It consists of 2 layer of dense fibrous tissue. The
outer layer takes place of peristeum which lies closest to skull
bone and the inner layer (meningeal layer), which lies closest to
the brain. The space between the skull & the dura mater called
epidural space & the space between dura & archnoid mater is
called subdural space.

The dura mater has following folds:-

 Flax cerebri:-
 Tentorium cerebelli
 Flax cerebelli
 Diaphragma sellae:-
 Flax cerebri:- Larger sickle shaped that separates the cerebral
hemispheres(either half of the cerebrum). The superior sagittal
sinus is formed by flax cerebri.
 Tentorium cerebelli:- the second largest; crescent shaped(moon
in shaped) that separates the occipital lobes from cerebellum. It
forms the straight & transverse sinuses.
 Flax cerebelli:- Vertical infolding that lies inferior to the
tentorium cerebelli separating the cerebellum. It forms the
straight & tranverse sinuses.
 Diaphragma sellae:- Smallest infolding covering the pituitary
gland & sella turcica.
 Arachnoid mater:- Is the middle layer of the meninges. The
archnoid mater is a thin transparent membrane. The arachnoid
mater also extends down like dura mater and ends at second
sacral vertebra, The space between archnoid & pia matter is
called sub archoid space which contain the cerebrospinal
fluid(CSF)
 Pia mater:- the pia mater is the innermost layer of meninges.it is
very thin , but it is thicker than the arachnoid mater. It is a very
delicated layer(highly vascularized) of connective tissue
containing many minute blood vessels and it adheres to the
surface of the brain , spinal cord. It dips into all sulci and
fissues. The spinal pia mater extends from the foramen
magnum(large oval opening in occipital bone) to the lower
border of the first lumber vertebrae and continues below as
filum terminale.
VENTRICLES OF THE BRAIN AND CEREBROSPINAL FLUID
 The brain contain 4 irregular – shaped cavity,: ventricles, where
CSF is produced within each ventricles is a region of choroid
plexus(a vascular plexus of the cerebral ventricles that regulate
intraventricular pressure), a network of ependymal cells(Thin
epithelial membrane lining the ventricles of the brain and spinal
cord canal) involved in production of CSF . The ventricles are
lined up with ependyma a specialized form of ventricles.
 Right and left lateral ventricles
 Third ventricles
 Fourth ventricle
 Right and left lateral ventricles:- These ventricles lie within the
cerebral hemisphere one on each side just below the corpus
callosum(is a wide, flat bundle of neural fibers about 10 cm long
beneath the cortex). They communicate with 3rd ventricle by a
inter ventricular foraming( foramina of Monro , are channels that
connect the paired lateral ventricles with the third ventricle at the
midline of the brain.).
 Third ventricles:- it is situated in the dienecephalon below lateral
ventricles between the two parts of thalamus. It communicates
with fourth ventricle by a canal the cerebral aqueduct.
 Fourth ventricle:- it is a diamond shaped cavity situated below &
behind the 3rd ventricle between cerebellum & pons . It is
continuous below the central canal of spinal cord & communicates
with subarchnoid space via cisterna magna.
 CEREBROSPINAL FLUIDS(CSF)
 CSF a clear , colourless & slightly alkaline fluids produced by
choroid plexus in the ventricles of the brain. CSF is secreted
continuously at a rate of 0.5 ml/min. The volume remains fairly
constant at about 150ml as reabsorption takes place through
arachnoid villi , which project into venous sinuses . The CSF
constites:-
 Water

 Mineral salt

 Glucose

 Plasma protein: small amount of albumin & globulin

 Urea , creatinine- in small amount

 A few leukocytes
CHARACTERISTICS:-
 Color: crystal clear
 Cell count:-0-4 cell/mm3

 Glucose; 2/3 of the blood glucose level(40- 60 mg/dl)

 Protein:- 20- 45mg/dl

 Specific gravity:- 1.003-1.008

 pH ;-7.31- 7.34

 Pressure:-10 - 18 cm of H2O (8- 15 mmHg in lying down position) : 20 - 30 cm

of H2O (16 – 24 mmHg in sitting position)
60 – 150 mm of CSF in supine and 200 – 250 mm of CSF in sitting position. And
newborn CSF pressure ranges from 8 to 10 cmH2O (4.4–7.3 mmHg)
 Circulating volume:- 120 – 150 ml of circulating volume
it is formed at the rate of about 20 ml per hour or 1500ml/day.
 Rate of absorption:- As rapidly as it is produced leaving 120 to 150 ml of
circulating volume,
 CSF turnover rate :-3.7 times/day

 1 cmH2O  = 0.76 mm Hg, 1 mm Hg = 1.36 cmH2O 

FUNCTION
 To cushion the soft tissues of the brain and spinal cord.
 To act as the medium for exchange of nutrients and waste
products in between the blood, brain and the spinal cord.
 Maintain intra cranial pressure around the brain & spinal cord
& act as a cushion or shock absorber.
 It keeps the brain & spinal cord moist & there may be
exchange of nutrient & waste products between CSF & nerve
cells.
BRAIN
The brain is an organ that serves as the center of the 
nervous system in all vertebrate and most invertebrate animals.
The brain is located in the head, usually close to the sensory
organs for senses such as vision. The brain is the most complex
organ in a vertebrate's body. In a human, the cerebral cortex
 contains approximately 15–33 billion neurons, ach connected by 
synapses to several thousand other neurons. These neurons
communicate with one another by means of long protoplasmic
 fibers called axons, which carry trains of signal pulses called 
action potentials to distant parts of the brain or body targeting
specific recipient cells.
The brain consists of
a. Cerebrum :- Cerebral cortex, Corpus callosus

b. The diencephalon:- Thalamus, pineal body,

hypothalamus
c. The brain stem:- Mid brain, pons, Medulla oblongata

d. Cerebellum

The brain receives about 15% of the cardiac

output per minute. The circle of willis or circulus
arteriosus & its contributing arteries plays a vital role
in maintaining supply of oxygen & glucose to the
brain.
 A) CEREBRUM
 It is the largest part of the brain & is divided by a deep cleft , the
longitudinal cerebral fissure , into right & left cerebral
hemispheres each containing one of the lateral ventricle .
 Deep within the brain ,the hemispheres are connected by a mass
of white matter called the corpus callosum. The peripheral part
of the cerebrum is composed of grey matter ,forming the cerebral
cortex & the deeper layer consists of white matter .
 Cerebral cortex shows many infoldings. The exposed area of fold
are the gyri & these are separated by sulci (fissures). It greatly
increase the surface area of cerebrum .
 Each hemispheres of cerebrum is divided into frontal , parietal ,
temporal & occipital lobes.
 The frontal :- These are the largest of all the lobe, and they
form the anterior part of the cerebral hemisphares. They are
located anterior to central sulci and superior to the lateral sulci.
 Parietal :- These lobes are related to the internal aspects of
posterior and superior part of the parietal bones. Each lobes is
bounded anteriorly by the central sulcus, posteriorly by the
superior part of the parieto- occipital sulcus and inferiorly by
the imaginary line extending from the posterior ramus of the
lateral sulcus.
 Temporal ;- These lobes lie inferior to the lateral sulci.

 Occipital lobes:- These lobe are relatively small and are

located posterior to the parieto occipital sulci although, these
lobes are very important because they contain visual area.
THE FUNCTIONAL AREA OF CEREBRAL CORTEX
i. The motor area
ii. The premotor area
iii. The motor speech area
iv. The sensory area
v. Visual area
vi. The auditory area(of hearing)
vii. The taste area
FUNCTION OF CEREBRAL CORTEX
 Mental activities involved in memory , intelligence, sense of
responsibility, thinking , reasoning , moral sense & learning.
 Sensory perception , including the perception of pain ,
temperature, touch, slight , hearing, taste & smell.
 Initiation & control of skeletal muscle contraction & therefore
voluntary movement.
The motor impulses arrive in the frontal lobe
immediately anterior to central sulcus & sensory impulses
arrive at the posterior part behind the the central sulcus.
 B) DIENCEPHALON
Diencephalon connects the cerebrum and midbrain. It consists of
mainly thalamus , hypothalamus & pineal body.
 Thalamus:- Thalamus is situated within cerebral hemispheres
just below corpus collosum. The main function of thalamus is to
relay motor & sensory signals to the cerebral cortex . It is also
involved in processing of some emotional & complex reflexes &
also regulates sleep, alertness & wakefulness.
 Hypothalamus:- It is a small but important structure situated
below & in front of thalamus , immediately above pituitary
gland. Hypothalamus control the output of hormones from both
lobe of pituitary gland. The other functions of hypothalamus
are:-
 Control of autonomic nervous system.
 Control of appetite & satiety.

 Control of thirst & water balance.

 Control of body temperature.

 Control of emotional reactions – pleasure , fear.

 Control of sexual behaviour & child rearing.

 Sleeping & waking cycles.

C) BRAIN STEM
It consists of mid brain, pons &medulla oblongata.
 Mid brain:- it is situated between the cerebrum & pons below . It
consists of nuclei 7 nerve fibers(tracts), which connect the cerebrum
with lower parts of the brain & the spinal cord. The nuclei act as relay
stations for ascending & descending nerve fibers.
 Pons:- It is situated in front of cerebellum, below midbrain & above
medulla oblongata. There are nuclei within the pons that act as relay
station & some of these are associated with cranial nerves. Others
form the pneumotaxic & apnoustic centre in the medulla oblongata.
 Medulla oblongata:- It extends from the pons above & is continuous
with the spinal cord below . It lies just within the cranium above the
foramen magnum. The outer aspect is composed of white mater &
grey matter is located centrally . Some cells constitute relay stations
for sensory nerve passing from spinal cord to cerebrum.
 The vital center located are:-
 Cardiovascular center
 Respiratory center
 Reflex center of vomiting , coughing, sneezing &
swallowing.
D) CEREBELLUM
 Cerebellum is situated behind the pons & immediately below
posterior portion of cerebrum. It has 2 hemispheres seprated by
a narrow median strip called the vermis . Grey matter forms the
surface & white matter lies deep inside the cerebellum.
 The cerebellum is concerned with the co – ordination of
voluntary muscular movement ,posture & balance , The
sensory input for these function is derived from muscle &
joints, eye & ears. Damage to cerebellum resulting in clumsy
uncoordinated muscle movement, staggering gait & inability to
carry out smooth , steady, precise movement.
SPINAL CORD
 The spinal cord consists of nerves that carry incoming and
outgoing messages between the brain and the rest of the body.
 The spinal cord is elongated, almost cylindrical part of the
CNS which is suspended in vertebral canal surrounded by the
meanings & CSF . Spinal cord is continues above with the
medulla oblongata & extends from the upper border of atlas to
the lower border of 1st lumber vertebra. Spinal cord is
composed of grey matter in the centre and white matter in the
peripheral . Spinal cord links the brain with rest of the body.
Nerves conveying impulses from brain to organ descends
through spinal cord & leave the cord at appropriate level.
Similarly , sensory nerve from organs & tissue enter & pass
upwards in spinal cord to the brain.
 Sensory nerve tracts in the spinal cord:- Nerves that transmit
impulses towards the brain are called sensory . The main
source of sensation are:- skin (Cutaneous receptors), tendons ,
muscles & joints(Proprioceptors)
 Motor nerve tract in the spinal cord:-Neurons that transmit
nerve impulses away from the brain are motor neurons. Motor
neurons stimulation results in :- contraction of skeletal
muscle(Voluntary)
- Contraction of smooth muscles (involuntary)
like cardiac muscle , secretion by glands
controlled by nerves of ANS
THE PERIPHERAL NERVOUS SYSTEM
The peripheral nervous system consists of :
 31 pairs of spinal nerves

12 pairs of cranial nerves

The autonomic nervous system

Sympathetic and

parasympathetic
 THE SPINAL NERVES
 A spinal nerve is a mixed nerve, which carries motor, sensory,
and autonomic signals between the spinal cord and the body.
 There are 31 pairs of spinal nerves that leave the vertebral canal
by passing through the intervertebral formina formed by adjacent
vertebra.

Spinal nerves are:-

 8 cervical

 12 thoracic

 5 lumber

 5 sacral

 1 coccygeal
 The lumber, sacral, coccygeal nerves leaves the spinal
cord near its termination at the level of 1st lumber
vertebra & extend downwards inside the vertebral canal
in the subarchnoid space , forming a sheaf(bundle) of
nerves which resembles a horses tail , the cauda equina.
The nerves leave the vertebral canal at the appropriate
lumber, sacral or coccygeal level.
PLEXUS:-
 In the cervical , lumber & sacral regions the anterior rami unit
near their origins to form large mass of nerves or plexus where
nerves fibers are regrouped & rearranged before proceding to
supply particular area :-
 Cervical plexuses:- Serves head , neck & shoulder

 Brachial plexus:- Serve chest, shoulder, arms & hands

 Lumber plexus:- Serves the back, abdomen, groin, thigh, knee, &
calves.
 Sacral plexus:- Serve the pelvic, buttocks, genitals, thigh, calves
& feet.
 Coccygeal plexus:- serves a small region over the coccyx.
THORACIC NERVES:-
 These nerves do not form plexus. There are 12 pairs & the first
11 are intercostal nerves which pass between ribs & supply
them , the intercostal muscle & skin overlying it. The 12th pair
comprise of subcostal nerves. The 7th to 12th thoracic nerves
also supply the mucus & skin of anterior & posterior abdominal
walls.
THE CRANIAL NERVES
 Cranial nerves are the nerves that emerge directly from the 
brain (including the brainstem), in contrast to spinal nerves
 (which emerge from segments of the spinal cord). Cranial
nerves relay information between the brain and parts of the
body, primarily to and from regions of the head and neck.
 There are 12 pairs of cranial nerves, some sensory , some
motor & some mixed . They are:-
No Names Types Function

I Olfactory Sensory Smell

II Optic Sensory Vision

III Oculomotor Motor Eyeball movement, focusing, regulation

IV Trochlear Motor Eyeball movement

V Trigeminal Mixed Chewing , sensation of the face

VI Abducent Motor Eye ball movement

VII Facial Mixed Sense of taste , facial expression

VIII Vestibulocochlear Sensory Hearing, balance

IX Glossopharyngeal Mixed Sensation of saliva, pharynx movement, swallowing

& gag reflex
X Vagus Mixed Enervates heart & major part of respiratory &
alimentary tract
XI Accessory Motor Movement of neck, shoulder, pharynx & larynx

XII Hypoglossal Motor Tongue movement.

 AUTONOMIC NERVOUS SYSTEM(ANS)
 ANS control the automatic or involuntary part of the nervous system control the
function of the body. The effector organs of ANS are:-
 Sooth muscle eg- change in blood vessels diameter

 Cardiac muscle eg:- change in rate & force of heart beart

 Glands eg:- regulating gastrointestinal secretions.

ANS has two branches:-

 Sympathetic (Thoracolumbar outflow)

 Para sympathetic(Craniosacral outflow)

Note:- The sympathetic division has thoracolumbar "outflow", meaning that the

neurons begin at the thoracic and lumbar (T1-L2) portions of the spinal cord. The
parasympathetic division has craniosacral "outflow",meaning that the neurons
begin at the cranial nerves (CN3, CN7, CN9, CN10) and sacral (S2-S4) spinal
cord.
SYMPATHETIC (PREDOMINATES IN
STRESSFUL SITUATION)
 Since the preganglionic neurons originates in the spinal cord at
the thoracic & lumber level , the atlernative name
thoracolumbar outflow has been given. It promotes a “Fight or
flight” response, promotes vasoconstriction , dilated
bronchioles of the lungs , increase heart rate & contractility of
cardiac cells, dilated pupil & relaxes ciliary muscle, provides
vasodilation for coronary vessels of the heart , constricts all
intestinal & urinary sphincter, inhibits peristalsis & stimulates
orgasm.
PARASYMPATHETIC (PREDOMINANT IN
SITUATION OF REST)
 It has been said to promote a “rest & digest” response,
promotes calming of nerves return to regular function &
enhancing digestion. It dilates blood vessels leading to GI
tract , constriction of pupils & contraction of cilliary muscles
facilitating accomodation & allowing for closer vision,
stimulating salivary gland secretion & accelerates peristalsis,
mediating digestion & absorption . It is also involved in
erection of genital tissue & stimulation sexual arousal.
  Unlike the sympathetic system, humans have some voluntary
controls in the parasympathetic system. The most prominent
examples of this control are urination and defecation.
DIFFERENCE BETWEEN SYMPATHETIC(SNS)
AND PARASYMPATHETIC(PNS)
1. The PNS can constrict the pupils of the patient while the SNS dilates
them.
2. The SNS inhibits the secretion of saliva whereas the PNS stimulates
this process.
3. The PNS decreases the pulse rate and slows down the blood pressure.
On the contrary, the SNS increases the pulse rate and heightens blood
pressure levels.
4. The PNS can also constrict the bronchi. On the other hand, the SNS
dilates them and increases their diameter.
5. The PNS can stimulate the digestive system activity while the SNS
inhibits its activity.
6. The SNS enables urinary retention whereas the PNS can stimulate
urination.
7. The rectum is relaxed when the patient’s PNS is activated. Inversely,
the rectum is contracted when the SNS is stimulated.
 Sympathetic System Parasympathetic System
Organ

Dilates pupil Constricts pupil

Eye

No effect Stimulates tear secretion

Tear glands

Inhibits saliva production Stimulates saliva production

Salivary glands

Dilates bronchi Constricts bronchi

Lungs

Speeds up heart rate Slows down heart rate

Heart

Inhibits peristalsis Stimulates peristalsis

Gut

Stimulates glucose Stimulates bile production

Liver production

Bladder Inhibits urination Stimulates urination

 DIFFERENCE BETWEEN CNS AND PNS
1. CNS refers to the Central Nervous System whereas PNS refers to the Peripheral
Nervous System.
2. The Central Nervous System comprises of the brain and the spinal cord whereas
the Peripheral Nervous System comprises of the autonomic nervous system and the
somatic nervous system.
3. The CNS handles involuntary information while the PNS handles voluntary
information.
4. The central nervous system, in vertebrates is placed inside the meanings (brain and
the spinal cord) and the PNS exists and extends outside the Central Nervous
System.
5. The prime function served by the Central Nervous System is that along with the
PNS it contributes a huge control on the organism’s behavior and the Peripheral
Nervous System is to connect the Central Nervous System with the various organs
in the body and the limbs.
6. The Central Nervous System is placed safely within the dorsal cavity, the brain
placed inside the cranial cavity and the spinal cord in the spinal cavity. The skull
protects the brain and the vertebra protects the entire spinal cord. But like the CNS
the Peripheral Nervous System is not protected by any bone or blood-brain barrier.
DIFFERENCE BETWEEN GREY AND WHITE
MATTER
1. Grey matter is made up of nerve cell bodies, and white matter is
made up of fibers.
2. Unlike the white matter, the neurons of grey matter do not have
extended axons.
3. Grey matter occupies 40 percent of the brain, while white matter
fills 60 percent of the brain.
4. Grey matter has a grey color because of the grey nuclei that
comprises the cells. Myelin is responsible for the white
appearance of the white matter.
5. Processing is concluded in the grey matter, while white matter
allows communication to and from grey matter areas, and
between the grey matter and the other parts of the body.
6. Grey matter has no myelin sheath, while white matter is
myelinated.
DIFFERENCES BETWEEN
MYELINATED AND UNMYELINATED
NEURONS
 A neuron that has myelin sheath cover would mean:
faster transmission
faster conduction
faster transfer of impulses
 DIFFERENCE BETWEEN NERVE AND
NEURON
1. A neuron is an individual cell, whereas, a group of neurons form
a nerve.
2. There are two types of neurons ‘“ sensory and motor neurons;
while there are three types of nerves ‘“ afferent, efferent and
mixed nerves.
3. Nerves are found in the peripheral nervous system, while
neurons are found in the brain, spinal cord and the peripheral
nerves.
4. A neuron can also be called a neurone or a nerve cell.
5. Neurons conduct nerve impulses, while nerves transmit
information to various parts of the body.
DIFFERENCE BETWEEN AXONS AND
DENDRITES
1. Dendrites receive electrochemical impulses from other
neurons, and carry them inwards and towards the soma, while
axons carry the impulses away from the soma.
2. Dendrites are short and heavily branched in appearance,
while axons are much longer.
3. Generally, dendrites receive neuron signals, and axons
transmit them.
4. Most neurons have a lot of dendrites and only have one axon.
5. Dendrites’ radius tapers, while axons’ remain constant.
 IMPORTANT QUESTION
 Define nervous system. And classify the nervous system.
 Define synapse and explain the types of synapse.

 Define nerves and explain the types nerves .

 Explain the mechanism of stimuli transmission (Actional potential).

 Describe the covering membranes of brain with diagram.

 List out the parts of brain, and explain its.

 Short note:-
a. Nerve cell
b. Nerve termination
c. Lobe of the brain
d. Ventricles of the brain
e. Gray matter
f. White matter
 Define CSF , and explain its composition and function of CSF.
 Explain the spinal cord.

 List out the peripheral nerves , and explain the spinal.

 List out the 12 pairs of cranial nerves with its function.

 Define plexuses. And list out the five large plexuses of the
body.
 Explain the sympathetic and parasympathetic nervous system.