Nervous System.pptx

Introduction:
• Living beings respond to changes in the external
environment.
• Constantly changing surrounding poses a great
threat to homeostasis.
• Internally there will be changes to suit the
alterations in the exterior.
• Various systems of the body are controlled by
nervous and endocrine systems.
• The regulatory mechanism are together called
neuro-endocrine control.

Introduction:
• A neuron ( also known as a neurone or nerve cell)
is an electrically excitable cell that processes and
transmits information by electrical and chemical
signaling.
• Neurons are the core components of the nervous
system, which includes the brain, spinal cord, and
peripheral ganglia.
• Human brain comprises tens of billions of neurons,
each linked to thousands of other neurons via the
chemical channels called synapse.

Structure of Neuron:
• There are many, many different types of neurons but almost
all have certain structural and functional characteristics in
common.
• A neuron consists of three main parts the cell body or
perikaryon or soma, dendrites and axons.
• The cell body is the central region which is the most
important part of the neuron containing the nucleus of the cell.
• The soma is, the site of major metabolic activity in the
neuron.
• The size of neuronal somas range widely from 0.005mm to
0.1 mm in mammals
• Collections of cell bodies (somas) give the greyish
appearance to the gray matter of the brain.

Cont…
• The protoplasm of cell body contains peculiar angular
granules, which stain deeply with basic dyes, such as
methylene blue; these are known as Nissl’s granules.
• These granules disappear (chromatolysis) during fatigue or
after prolonged stimulation of the nerve fibers connected with
the cells. They are supposed to represent a store of nervous
energy, and in various mental diseases are deficient or absent.
• Thought to be involved in the synthesis of neurotransmitters
such as acetylcholine.
• Dendrites are extensions that carry impulses toward the cell
body and are referred to as being afferent fibers.
• They effectively increase the surface area of a neuron to
increase its ability to communicate with other neurons.

Cont…
3. Axon: It is the long process of a neuron.
• It arises from the prominent portion of the cell
body called the axon hillock.
• Axons carry information away from the cell
body.
4. Axon telodendria(terminal buttons): These are
the terminal portion of axon, which divides into
branches. They contain vesicles with the neuro-
transmitter.

Cont…
5. Neuro-filaments: They form the cytoskeleton and
provides structural support to the neuron.
• Axons are called nerve fibers.
• Nerve fibers are covered by connective tissue
layer called endoneurium.
• Several such fibers form a bundle and are
enclosed in a sheath called perineurium.
• These bundles are termed fascicles.
• Several bundles are enclosed by the outer most
layer called epineurium.

Classification of Neuron:
1. Based on the number of processes
a) Unipolar neuron: The neuron has a single process.
b) Bipolar neuron: The neuron has two processes.
c) Multipolar neuron: The neuron has more than two
processes.
d) Pseudo-unipolar neuron: is a type of neuron which
has one extension from its cell body. This type
of neuron contains an axon that has split into two
branches; one branch travels to the peripheral nervous
system and the other to the central nervous system.

Cont…
2. Based on myelination:
a) Myelinated nerve fibre: Nerve fiber is covered by the
myelin sheath.
b) Non-myelinated nerve fibre: Nerve fibre lacks the covering
of myelin sheath.
3. Based on functions:
a) Sensory or afferent: They carry information from periphery
to the central nervous system.
b) Motor or efferent: these neurons carry motor impulses from
central nervous system to the effector organs.
c) Interneurons: They connect neurons within the central
nervous system.

Cont…
4. Depending upon the neurotransmitter secreted:
a) Adrenergic neuron: Secrete adrenaline at the
nerve terminal.
b) Cholinergic neuron: Secrete acetylcholine at
the nerve terminal.

Resting membrane potential(RMP):
• It is the potential difference existing across the cell
membrane at rest.
• It keeps the cell in an excitable state.
• Inside of the cell is negative in relation to the exterior.
• Sodium and potassium ions play an important role in
the generation of resting membrane potential.
• In a motor nerve, resting membrane potential is about
-70mV, It means that the intracellular fluid has an
excess of negative charge and the potential difference
across the membrane has a magnitude of 70mV.
• In the muscle RMP ranges from -80 to -90mV.

Action potential:
• It is an electrochemical change occurring in the
excitable tissue in response to threshold stimulus.
• It has the phases of depolarization and
repolarization.
• Action potential are large, rapid alterations in the
membrane potential showing a fluctuation of
about 100mV(from -70mV to+30mV).
• Nerve, muscle, endocrine, immune and
reproductive cells have plasma membrane capable
of producing action potential.

Ionic basis of action potential:
• Stimulation of motor nerve with minimal stimulus increases
permeability of the membrane to sodium ions.
• Sodium ions start entering into the cell.
• Inside of the cell tends to move towards the positive side.(a
slight decrease in resting membrane potential leads to
increased potassium efflux and chloride influx restoring
resting membrane potential.
• At around -55mV(firing level), permeability of the
membrane increases to sodium ions significantly resulting
in its explosive entry.
• Sudden influx of sodium makes inside of the cell relatively
positive. There is reversal of polarity. This phase is termed
Depolarization.

Cont…
• During depolarization, potential difference across the membrane
become zero. This is termed isoelectric potential. Subsequently it
becomes positive inside.
• On reaching a maximum of +35mV(spike potential), sodium
channels are inactivated and potassium channels open.
• Potassium ions move out of the cell.
• There is restoration of potential. This phase is termed
repolarization.
• Potassium continues to move out of the cell in spite of reaching the
resting level. Inside of the cell becomes relatively more negative.
This phase is termed hyperpolarization.
• Hyperpolarization reduces excitability of the cell.

Nerve Impulse:
• Action potential is generated at the site of stimulation. It travel along
the nerve fibre.
• The travelling action potential constitutes an impulse.
• Thus an impulse is defined as self-propagating physic-chemical
change.
• Transmission of nerve impulse:
 Stimulation of the motor nerve results in depolarization at the site of
stimulation.
 Inside of the cell becomes positive in relation to exterior.
 Positive charges move forwards to the segment ahead within the
cell.
 Positive charges are drawn backwards from the segment ahead
outside the cell.
 There is a drop in the positive charges outside the cell termed as
current sink.

Neuromuscular Junction:
• It is a specialized area where a motor nerve
ends on the skeletal where a motor nerve ends
on the skeletal muscle fibre.
• Junction between the autonomic neurons with
smooth and cardiac muscle is not well formed.
• Therefore the transmission of impulse across
these junctions is diffuse.

Cont…
• Neuromuscular junction consist of:
1. Pre-junctional membrane: This is the terminal
part of motor nerve with vesicles containing
acetylcholine.
2. Synaptic cleft plate: It is a potential space
between the nerve terminal and muscle.
3. Motor end plate: This is the muscle
membrane containing acetylcholine receptors.
It forms the post-junctional membrane.

Synapse:
• Synapse is a junction between two neurons where
information from one nerve terminal is relayed to
the other neuron.
• Neuron which ends at the synapse is termed pre-
synaptic neuron. Neuron which receives the
information is post-synaptic neuron.
• The electrical activity of pre-synaptic neuron
influences the activity in the post-synaptic
neuron.
• There are about 10 synapses in CNS.

Structure of synapse:
• A typical chemical synapse has:
1. Pre-synaptic terminal with neuro-transmitter
in the vesicles.
2. Synaptic cleft or synaptic gutter.
3. Post-synaptic terminal with receptors for
neuro-transmitter.

Reflex action:
• Reflex action is an involuntary response to a sensory
stimulus. It occurs at the spinal level.
• E.g. Withdrawal of the hand on touching a hot object.
• The reflex action is produced with the help of a reflex arc.
• Reflex arc consist of
1. Receptor- A modified nerve terminal with a group of
special cells capable of receiving different types of stimuli.
2. Sensory or afferent nerve.
3. Synapse or the center present in the spinal cord.
4. Motor or efferent nerve.
5. Effector organ- Muscle or a gland.

Bell Magendie law:
• It states that the dorsal or posterior root entering the spinal
cord is sensory and ventral or anterior root emerging from
the spinal cord is motor.

Receptors
• Receptors are modified nerve terminals capable of
converting different forms of energy to electrical energy.
• Classification:
1. Exteroceptors: These receptors are capable of recognizing
changes in the external environment. E.g. Receptors for
touch, Pain and temperature.
2. Interoceptors: These receptors respond to alterations in the
internal environment. E.g. Baroreceptors and
chemoreceptors.
3. Telereceptors: They perceive changes in the surroundings
from a distance. E.g. Receptors for vision and audition.
4. Proprioceptor: They provide information about orientation
of different parts of the body in space. E.g. Muscle spindle
and Golgi tendon organ.

Receptor types:
• General sensations:
1. Touch and pressure: Rapidly adapting-
Meissner’s corpuscles and pacinian corpuscles.
• Slowly adapting- Merkel’s disc.
2. Pain: Free nerve ending.
3. Temperature: Ruffinis end organ.
4. Joint sense: Muscle length- Muscle spindle.
• Muscle tension- Golgi tendon organ.
5. Linear and rotational acceleration Hair cells of
vestibular apparatus.

Cont…
• Special sensation:
1. Vision: Rods and cones.
2. Audition: Hair cells of organ of Corti.
3. Taste: Taste receptor cells of taste buds.
4. Smell: Olfactory neurons.

Pain:
• Pain is an unpleasant, subjective sensation
produced due to the nerve damage. It warns
the people about the possible damage to the
tissue.
• Crude sensation of pain can be appreciated at
the thalamic level where as finer aspects of it
can be perceived at the cortical level.
• Sense organs for pain are free nerve endings
present in all the tissues.

Pain is of two major types:
1. A sharp, localized fast pain carried by Aẟ fibres. These
nerve fibres have a diameter of 2-5µ and conduct
impulses at the rate of 15-30m/sec.
2. A poorly localized, dull aching slow pain carried by C
fibres. These are un-myelinated fibres having a
diameter of 0.4-1.2µ. They carry impulses at the rate
of 0.5-2m/sec.
• The sensation of pain is produced by substances like:
1. Prostaglandins.
2. Bradykinin.
3. Serotonin.

Cont…
• Pain is produced due to following changes in
the body:
1. Inflammation.
2. Obstruction.
3. Ischemia.
4. Distension of hollow viscus.
5. Muscle spasm.
6. Dilatation of blood vessels.

Referred Pain:
• It is the pain from an internal organ felt in an area
of skin away from site of its production.
• Examples:
1. Pain produced due to the MI damaged is referred
to left shoulder and ulnar aspects of left upper
limb.
2. Pain produced due to inflammation of liver and
gallbladder is felt in the right shoulder.
3. Pain produced due to the inflammation of
appendix is felt initially around the umbilicus.a

Nervous system:
• The nervous system is divided into
1. Central nervous system consisting of – Brain
and Spinal cord.
2. Peripheral nervous system consisting of- 12
pairs of cranial nerves and 31 pairs of spinal
nerves.
3. Autonomic nervous system comprising of –
sympathetic division and parasympathetic
division.

Central nervous system:
• CNS is enclosed by
1. Dura mater
2. Arachnoid mater.
3. Pia mater.
• Central nervous system consists of:
1. Cerebrum.
2. Cerebellum.
3. Brain stem.
4. Midbrain.
5. Pons
6. Medulla Oblongata.
7. Cerebral ventricles.
8. Spinal cord.

Cont…
1. Cerebrum: It occupies major part of the cranial
cavity.
• It has right and left hemispheres.
• Cerebral hemispheres have outer shell of gray
matter termed cerebral cortex.
• Myelinated fibre tracts form the white matter.
Two cerebral hemispheres are connected by
bundle of nerve fibres called corpus callosum.
• Cells of the cerebral cortex are arranged in six
layers.

Cont…
2. Cerebellum: It is located posterior and inferior to
the cerebrum.
• It has two cerebellar hemispheres.
• It is an important centre for coordinating
movements, controlling posture and equilibrium.
• It receives information from muscles, joints, eyes,
ears, viscera and the parts of brain involved in the
control of movements.
• Cerebellum not only performs motor functions
but is also involved in the process of learning.

Cont…
3. Brain stem: It consists of midbrain, pons and medulla
oblongata. The core of brain stem consists of loosely arranged
neuronal cells with bundles of axons termed reticular
formulation.
4. Midbrain: It is the part of brain stem located between
cerebrum above and pons below. Midbrain has nerve fibres
and cells bodies connecting cerebrum and spinal cord. It acts
as a relay station for nerves passing through it.
5. Pons: It is located above the medulla oblongata, in front of
cerebellum and below midbrain. It has nerve fibres connecting
spinal cord and midbrain as well as fibres between cerebellar
hemispheres. Nerve fibres are located superficially and cell
bodies are deeply placed in pons.

Cont…
6. Medulla oblongata: It extends between pons
above and spinal cord below. Gray matter is
located centrally and white matter is on the
surface. Deeper parts of medulla contain vital
structures, which regulate autonomic reflex
activity.
7. Cerebral ventricles: Brain contains four
interconnected cavities called cerebral ventricles.
It is filled with circulating cerebrospinal fluids.

Cont…
8. Spinal cord: It is an extension of medulla oblongata and is
located in the bony vertebral column. It has outer white matter
and inner grey matter. Central canal, which is a continuation of
cerebral ventricles, pass through the spinal cord.
• Cell bodies of neuron group together in CNS to form gray
matter and the fibres form white matter.
• In the brain, gray matter is outside and the white matter is
inside.
• Cell bodies of neuron collect together to constitute the
nuclei and fibres join to form the tract.
• Inputs reach the brain through the sensory receptors and
sensory division of nervous system.
• Brain acts as an information gathering, data analyzing and
decision-making device. Useful information is stored as
memory.

Cont…
• The desired response is produced with the help of motor
division of nervous system. It will result in contraction of
the muscle or secretion from the gland.
• Spinal cord gives out segmental nerves. There are 31 spinal
segments with 31 pairs of nerves.
1. Cervical : 8
2. Thoracic :12
3. Lumbar :5
4. Sacral :5
5. Coccyx :1
• A typical spinal nerve is a mixed nerve. It has sensory
division located in the dorsal root. Cell body of the afferent
nerves is in dorsal root ganglion.

Cont…
• Ventral division is motor and carries somatic
efferent to the muscles. The anterior root of spinal
nerve from T1 to L2 segments carries sympathetic
efferents. Parasympathetic fibres are carried by
spinal nerve from S2-4 segments.
• In addition to neurons, the nervous system has the
supporting cells called neuroglia.
• Neuron is the structural and functional unit of
nervous system. There are about 100 billion
neurons in the central nervous system.

Motor system:
• Descending pathways are motor tracts. They
are broadly divided into pyramidal and extra
pyramidal system.
1. Pyramidal system: Corticospinal tract is the
main tract of pyramidal system.
2. Extrapyramidal system: tracts of the extra
pyramidal system are Tectospinal tract,
Rubrospinal tract, Reticulospinal tract,
Vestibulospinal tract, Olivospinal tract.

Upper motor neuron lesion:
• Damage to pyramidal tract from its origin in the
cerebral cortex to anterior horn cell is termed upper
motor neuron lesion. It has the following features.
1. Voluntary movements are lost.
2. Muscle tone is increased- Spasticity.
3. Deep reflexes exaggerated, ankle and patellar clonus
present.
4. Superficial reflexes are lost.
5. Babinski’s sign becomes positive.
6. In long standing cases there is atrophy of muscle due
to disuse. E.g: Hemiplegia.

Lower Motor Neuron Lesion:
• Lesion in anterior horn cell or the nerve from anterior horn
cell to its termination results in lower motor neuron lesion.
• It shows following features:
1. Loss of voluntary motor activity.
2. Hypotonia – flaccid paralysis.
3. Absence of superficial and deep reflexes in the affected
segment.
4. Muscles supplied by the affected nerves progressively
atrophy.
5. Fibrillation potential seen in electromyogram.
6. Reaction of degeneration present. E.g: Poliomyelitis.

Clinical Notes:
1. Hemiplegia: Paralysis of one half of the
body.
2. Paraplegia: paralysis of both the lower
limbs.
3. Monoplegia: Paralysis of any one limb.
4. Quadriplegia: Paralysis of all the four limbs.

Hypothalamus:
• It is present under the surface of brain. It is situated below the
thalamus.
• It extends from optic chiasma anteriorly to mammillary body
posteriorly. Hypothalamus weight about 4g.
• Functions:
1. Control of food intake.
2. Regulation of water balance.
3. Control of anterior pituitary.
4. Control of posterior pituitary.
5. Regulation of body temperature.
6. Control of autonomic functions.
7. Control of sleep and wakefulness.
8. Control of circadian rhythm.
9. Control of behavior.

Thalamus:
• Thalamus is an oval mass containing groups of nuclei
forming the lateral boundary of third ventricle. It forms
partly the floor of lateral ventricle.
• Functions:
1. It is a sensory relay station. It relays general and special
sensation except smell sensation except smell sensation.
2. It functions as subcortical centre for perception of pain
sensation.
3. It helps in information storage and short-term memory.
4. It forms a functional part of reticular activating system
responsible for consciousness, sleep and wakefulness.
5. It forms a part of neural circuit (papez) for emotional
experience, personality and social behavior.

Cont…
6. It regulates autonomic functions associated with
emotions.
7. It forms a part of posture adjusting system. It
helps the motor cortex to modify and update
signals to perform voluntary motor activity.
8. It integrates cortical and subcortical areas for
execution of speech.
9. It plays an important role in genesis and
synchronization of waves of EEG.
10.It forms a link between cerebellum, basal ganglia
and cerebral cortex.

Basal Ganglia:
• Basal ganglia is a subcortical structure located lateral to
thalamus, below the lateral ventricle. It is located lateral to
third ventricle consisting of following nuclear groups.
 Caudate nucleus
 Putamen.
 Globus pallidus: External segment, Internal segment.
 Substantia nigra: Pars compacta, Pars reticulate.
 Sub thalamic nucleus(Red nucleus).
• Important neurotransmitters in the basal ganglia are:
1. Dopamine
2. GABA
3. Acetylcholine.

Functions:
1. It is responsible for planning and programming voluntary
motor activity.
2. It regulates stretch reflex throughout the body.
3. It controls the transfer of information from sensory and
association areas to motor cortex.
4. Essential for initiation, control and cessation of muscular
activity.
5. It provides the necessary muscle tone for skilled movements.
6. It co-ordinates the impulses for skilled motor activity.
7. It controls the normal autonomic associated movements.
8. It regulates the subconscious gross associated movements.
9. Intact basal ganglia is necessary for normal degree of tone and
posture.

Clinical notes:
• Parkinsonism: Lesions of basal ganglia results in parkinsonism. In this
condition, dopaminergic pathway is damaged.
• It shows the following hypokinetic features:
1. Rigidity of muscle-lead pipe type/cog wheel type.
2. Resting tremors (pill rolling tremors).
3. Flexed attitude due to increased tone in the flexor muscles.
4. Difficulty to commence the movements (akinesia).
5. Difficulty in execution of movements and slowness of movements
(bradykinesia).
6. Poverty of movements.
7. Loss of associated movements.
8. Short shuffling gait (festinent gait).
9. Autonomic disturbances.
10. Loss of facial expression – mask like face.

Cont…
• Hyperkinetic features of parkinsonism are
Chorea, athetosis, ballismus. These are
excessive abnormal involuntary movement.
• Management: This condition can be managed
by administration of L dopa (precursor of
dopamine) as dopamine cannot cross the blood
brain barrier.

Cerebral cortex:
• It occupies major part of the cranial cavity. It has right and
left hemispheres. It is separated by flax cerebri.
• Cerebral hemispheres have outer shell of grey matter
termed cerebral cortex.
• Myelinated fibres arranged as tracts from the white matter.
• Two cerebral hemispheres are connected by bundle of nerve
fibres called corpus callosum.
• The cortex is thrown into number of folds. These are called
gyri or convolutions.
• Deeper groves are termed fissures.
• The raised portions between the gyri are sulci.
• The longitudinal fissure divides cerebrum into right and left
cerebral hemispheres.

Cont…
• Cerebral cortex is divided into 4 lobes. These lobes are
named on the basis of bones that cover them.
• The lobes are Frontal lobe, Parietal lobe, Temporal lobe and
occipital lobe.
• The major areas are:
1. Frontal lobe:
Area no 6: It is the primary motor area. It lies in front of
central sulcus.
Area no 6: It is the premotor area.
Area no 8: Frontal eye field area- This helps in voluntary and
conjugate movements of the eye.
Area no 44: Broca’s speech area- present in dominant
hemisphere. It helps in vocalization.

Cont…
2. Parietal lobe:
Area no 3,1 ands 2: Primary sensory cortex(somato
sensory area) present in post-central gyrus.
Area No 5 and 7: Sensory association areas.
3. Occipital lobe:
Area no 17: primary visual area.
Area no 18 and 19: Visual association areas.
4. Temporal lobe:
Area no 41 and 42: Primary auditory area.
Area no 22: Wernicke’s area- concerned with
interpretation of sound.

Cerebellum:
• It is located posterior and inferior to the cerebrum. It is
separated from cerebrum by a transverse fissure. It has two
cerebellar hemispheres and central constricted part called
vermis.
• Anatomically it is divided into: Anterior lobe, Posterior lobe
and Flocculo-nodular lobe.
• Cerebellum has the following functional divisions:
1. Vestibulo cerebellum (Archi cerebellum)
2. Spino cerebellum (paleocerebellum)
3. Cerebro-cerebellum (Neocerebellum)
• Nuclei of cerebellum are: Nucleus Globosus, Nucleus
Embolioformis, Nucleus Fastigius, Nucleus Dentatus.

Cont…
• Superficial layer of cerebellum is cerebellar cortex.
• It is made of gray matter. Gray matter is arranged in the
form of ridges called folia. Deeper parts of cerebellum
have tracts which form white matter.
• Cerebellar nuclei are situated in white matter.
• Cerebellum is attached to brain stem with the help of
cerebellar peduncles.
• The cerebellar peduncles are:
1. Superior cerebellar peduncle.
2. Middle cerebellar peduncle.
3. Inferior cerebellar peduncle.

Functions of cerebellum:
1. Vestibulo cerebellum (Archi cerebellum)- it is concerned
with maintenance of balance and equilibrium.
• It is responsible for regulating the stability of head and body
in space.
• It adjusts the tone of the trunk muscle.
• Controls the ocular movements and other postural reflexes.
2. Spino cerebellum (paleocerebellum)- Maintains the
posture and helps in execution of gross movements.
• It controls the interplay between the agonist and antagonist
group of muscles.
• It is essential for the control of rapid muscular activities like
running and talking.

Cont…
3. Cerebro-cerebellum (Neocerebellum)-
• Controls fine, highly precise and co-ordinated
movements.
• It is involved in programming of voluntary and
skilled movements.
• It plays a major role in the timing of the motor
activities and rapid progression from one
movement to the next.

Brain stem
• It consists of midbrain, pons and medulla
oblongata.
• The core of brain stem consists of loosely
arranged neuronal cells with bundles of axons
termed reticular formation.
• Reticular formation is absolutely essential for life.
It is involved in control of motor functions,
cardiovascular and respiratory activities.
• It regulates sleep and wakefulness cycle.

Midbrain or Mesencephalon:
• It is a part of brain stem located between cerebrum above
and pons below.
• Anterior part of midbrain has tracts called cerebral
peduncles.
• They contain fibres of corticobulbar tracts.
• Midbrain has never fibres and cell bodies connecting
cerebrum and spinal cord. It also contains sensory fibres
from spinal cord to thalamus.
• It acts as a relay station for nerves passing through it.
• Posterior part of midbrain is called tectum. It has four
rounded elevations. Two superior colliculi and two inferior
colliculi.
• Superior colliculi act as reflex centre for visual activities.

Cont…
• Inferior colliculi act as reflex centre for
audition or hearing.
• Midbrain also contains Substantia nigra. It
controls subconscious muscle activities.
• Red nuclei located in midbrain co-ordinate
with cerebellum to produce muscular
movements.
• Nuclei of oculomotor and trochlear(cranial)
nerves are also present in midbrain.

Pons:
• Pons is located above medulla oblongata, in front of cerebellum and
below midbrain. It has nerve fibres connecting spinal cord and
midbrain as well as fibres between cerebellar hemispheres.
• Nerve fibres are located superficially and cell bodies are deeply
placed in pons.
• Bulged portion of Corticospinal tract in pons forms pyramid. The
oval shaped swelling lateral to pyramid is called olive. Inferior
olivary nucleus present in olive relays joint sensation to cerebellum.
• Pons contains centres regulating respiration. They are pnemotaxic
centre and apneustic centre.
• Nuclei of trigeminal, abducent, facial and vestibulocochlear nerves
are present in pons.
• The impulses for voluntary movement produced by cerebral cortex
reach cerebellum through pontine nuclei.

Medulla Oblongata:
• It extends between pons above and spinal cord below. Gray matter is
located centrally and white matter is on the surface. Deeper parts of
medulla contain vital structures, which regulate autonomic reflex
activity.
• The structure are:
a) Cardiac centre.
b) Respiratory centre.
c) Vasomotor centre.
d) Centres controlling coughing, sneezing, swallowing and vomiting.
• Cardiac centre regulates rate and force of cardiac contraction.
• Respiratory centre controls rate and depth of respiration. It
responds to changes in carbon-dioxide and oxygen content in the
blood. It alters the pattern of respiration.

Cont…
• Vasomotor centre: Regulates the size of blood vessels.
Alterations in size of blood vessel changes the peripheral
resistance. By altering peripheral resistance, it controls
blood pressure.
• Others centres like coughing, sneezing and vomiting centre
located in medulla oblongata help to protect the body
against toxic and irritant substances.
• White matter of medulla contains sensory and motor tracts.
Gracile and cuneate nuclei connected with sensation of
touch, vibration are present in posterior part of medulla.
• Medulla also contains nuclei of vestibulocochlear,
glossopharyngeal, vagus, accessory and hypoglossal nerves.

Spinal cord:
• It is the elongated part of central nervous system.
• Spinal cord is a continuation of medulla oblongata.
• It extends from upper border of atlas above to lower border
of 1st lumbar vertebra below.
• It is present in vertebral canal surrounded by meninges and
cerebrospinal fluid.
• Central canal passes through centre of spinal cord.
• Meninges covering the spinal cord have three layers: They
are Outer Dura mater, Middle Arachnoid mater, Inner
Piamater.
• The space between dura mater and wall of vertebral canal is
called epidural space.

Cont…
• Space between dura mater and arachnoid mater is termed
subdural space.
• The region between arachnoid mater and pia mater is
subarachnoid space. It contains cerebrospinal fluid.
• The following are external features of the spinal cord:
1. Spinal nerves emerge in pairs, one from each side of the
spinal cord along its length.
2. The cervical nerves form a plexus (a complex interwoven
network of nerves—nerves converge and branch).
3. The cervical enlargement is a widening in the upper part of
the spinal cord (C 4–T 1). Nerves that extend into the upper
limbs originate or terminate here.

Cont…
4. The lumbar enlargement is a widening in the lower part of
the spinal cord (T 9–T 12). Nerves that extend into the
lower limbs originate or terminate here.
5. The anterior median fissure and the posterior median
sulcus are two grooves that run the length of the spinal
cord on its anterior and posterior surfaces, respectively.
6. The cauda equina are nerves that attach to the end of the
spinal cord and continue to run downward before turning
laterally to other parts of the body.
7. There are four plexus groups: cervical, brachial, lumbar,
and sacral. The thoracic nerves do not form a plexus.

Spinal Nerves:
• There are 31 pairs of spinal nerves (62 total).
• The following discussion traces a spinal nerve as it emerges
from the spinal column:
• A spinal nerve emerges at two points from the spinal cord,
the ventral and dorsal roots.
• The ventral and dorsal roots merge to form the whole spinal
nerve.
• The spinal nerve emerges from the spinal column through
an opening (intervertebral foramen) between adjacent
vertebrae. This is true for all spinal nerves except for the
first spinal nerve (pair), which emerges between the
occipital bone and the atlas (the first vertebra).

Cont…
• Outside the vertebral column, the nerve divides
into the following branches:
– The dorsal ramus contains nerves that serve the dorsal
portions of the trunk.
– The ventral ramus contains nerves that serve the
remaining ventral parts of the trunk and the upper and
lower limbs.
– The meningeal branch reenters the vertebral column
and serves the meninges and blood vessels within.
– The rami communicantes contain autonomic nerves
that serve visceral functions.

Cont…
• Anterior rami join together in cervical, lumbar and
sacral regions to form nerve plexuses. In the plexuses,
nerve regroup and supply a particular area of the body.
There are five such plexuses of mixed nerve formed by
the side of vertebral column. The plexuses are:
a. Cervical plexus.
b. Brachial plexus.
c. Lumbar plexus.
d. Sacral plexus.
e. Coccygeal plexus.

Cervical Plexus:
• The cervical plexus is formed by the ventral
rami of the upper four cervical nerves and the
upper part of fifth cervical ventral ramus.
• The network of rami is located deep within the
neck.
• It is covered by Sternocleidomastoid muscle.
• Serves the Head, Neck and Shoulders.
• It supplies muscles of diaphragm and help in
the process of respiration.

Brachial plexus:
• The brachial plexus is formed by the ventral rami of C5–C8 and the
T1 spinal nerves, and lower and upper halves of the C4 and T2
spinal nerves.
• The plexus extends toward the armpit (axilla).
• Serves the Chest, Shoulders, Arms and Hands
• The following nerves arise from brachial plexus.
1. Axillary nerve: it passes around neck of humerus. It supplies to
shoulder joint, deltoid muscle and the skin in that region.
2. Radial nerve: Supplies triceps muscle, extensors of wrist and
finger joint. It supplies skin of thumb, first two fingers and lateral
side of third fingers.
3. Musculocutaneous nerve: Supplies muscles of upper arm and skin
of the forearm.

Cont…
4. Median nerve: passes close to brachial artery in front of
elbow joint. It supplies muscles of front of forearm, small
muscles of hand and skin over thumb, first two fingers,
lateral side of third fingers.
5. Ulnar nerve: Lies medial to brachial artery in the upper
arm. It supplies muscles on ulnar side of forearm passing
behind medial epicondyle of humerus.
6. Medial cutaneous nerve: It is branch of medial cord of
brachial plexus. It passes medial to axillary and brachial
artery. It supplies skin of medial side of forearm, small
muscles of palm, skin over little finger and medial side of
third fingers.

Lumbar Plexus:
• The lumbar plexus is formed by the ventral rami of L1–L5 spinal nerves
with a contribution of T12 form the lumbar plexus.
• This plexus lies within the psoas major muscle.
• The branches of lumbar plexus are:
1. Ilioinguinal nerve, iliohypogastric nerve and genitofemoral nerve
suppplies muscles and skin of inguinal region, lower abdomen and medial
side of thigh.
2. Lateral cutaneous nerve supplies skin of lateral side of thigh.
3. Femoral nerve enters the thigh close to femoral artery after passing
behind inguinal ligament. It supplies skin and muscles in front of thigh.
Saphanous nerve which is a branch of femoral nerve supplies medial side
of leg, ankle and foot.

Cont…
4. Obturator nerve supplies adductor muscles of
thigh and skin of medial side of thigh.
5. Lumbosacral nerve: helps in the formation of
sacral plexus.

Sacral Plexus:
• The sacral plexus is formed by the ventral rami of L4-S3,
with parts of the L4 and S4 spinal nerves.
• It is located on the posterior wall of the pelvic cavity.
• Serves the Pelvis, Buttocks, Genitals, Thighs, Calves, and
Feet
• It forms the Sciatic nerve: (L4,5.S1,2,3.) It is the largest
nerve in the body. It passes through greater sciatic foramen
and supplies hamstring muscles. Sciatic nerve divides to
form tibial and common peroneal nerve at the middle of
femur.
• Tibial nerve: Reaches posterior side of the leg after passing
through popliteal fossa. It supplies muscles and skin of leg,
sole of foot and toes.

Cont…
• Sural nerve: A branch of tibial nerve supplies the
region of heel, lateral side of ankle and dorsum of
foot.
• Common peroneal nerve: reaches front of leg
passing around neck of fibula. It divides into
superficial personal(Musculo cutaneous) and deep
peroneal (anterior tibial)nerves. These nerve
supply anterior part of leg, dorsum of foot and
toes.
• Pudendal nerve (S2,3,4) (perineal branch)
supplies external anal and urethral sphincter.

Coccygeal plexus:
• It is formed by part of fourth and fifth sacral
nerves along with coccygeal nerves.
• Nerves of coccygeal plexus supply skin and
some muscles of pelvic floor and anal
sphincter.
• Serves a Small Region over the Coccyx

Thoracic nerves:
• There are 12 pairs of thoracic nerves.
• First 11 pairs pass between ribs.
• There are called as intercostal nerves.
• They supply ribs and intercostal muscles.
• 12th pair is called subcostal nerve.
• Lower intercostal nerves supply skin and
muscles of anterior and posterior abdominal
wall.

Dermatome
• A dermatome is an area of skin that is supplied by
a single spinal nerve, and a myotome is a group of
muscles that a single spinal nerve root innervates.
• A dermatome is an area of skin that is supplied by
a single spinal nerve. There are eight cervical
nerves, twelve thoracic nerves, five lumbar nerves
and five sacral nerves.
• Each of these nerves relays sensation, including
pain, from a particular region of the skin to the
brain.

Cranial nerves:
• There are 12 pairs of cranial nerves. They arise from base of brain. The
nerves are sensory, motor or mixed (both sensory and motor).
• The cranial nerves are:
1. Olfactory
2. Optic
3. Oculomotor
4. Trochlear
5. Trigeminal
6. Abducent.
7. Facial
8. Vestibulocochlear
9. Glossopharyngeal
10. Vagus
11. Accessory
12. Hypoglossal.

Nerve injury:
• Neuron do not multiply during life. Fortunately injury
to a peripheral nerve fibre(axon) does not destroy the
neuron. Damaged neuron can undergo repair and
become functional.
• Wallerian Degeneration: When a nerve fibre is
injured, part of nerve fibre distal to the site of the injury
undergoes changes. This process is known as Wallerian
degeneration.
• Regeneration of damaged nerve fibre: If the cut end
of the neurilemma is bought close to each other(less
than 3mm), the axis cylinder will grow into the
neurilemmal tube. Later there is formation of cells of
Schwann and myelin sheath.

Cerebrospinal Fluid(CSF):
• It is the fluid present in the ventricles of the brain, central
canal of spinal cord and subarachnoid space.
• Choroid plexus of lateral and third ventricle of brain forms
CSF by the processes of filtration and secretion.
• It passes through 4th ventricle, central canal in spinal cord
and finally gets absorbed in the arachnoid villi present in
sagittal sinus.
• The volume of CSF is about 150 ml.(however about 500 ml
of CSF is produced per day)
• It is colorless transparent fluid with a specific gravity of
1005.
• It is alkaline in reaction.
• CSF contains 99% of water and 1% solids.

The pathway of the cerebrospinal
fluid is as follows:
• The CSF passes from the lateral ventricles to the third ventricle through
the interventricular foramen.
• From the third ventricle, the CSF flows through the cerebral aqueduct (of
Sylvius) to the fourth ventricle.
• From the fourth ventricle, some CSF flows through a narrow passage called
the obex and enters the central canal of the spinal cord. However, the
majority of CSF passes through the apertures of the fourth ventricle;
the median aperture and two lateral apertures . Via these openings, the CSF
enters the cisterna magma and cerebellopontine cisterns, respectively.
• From there, the CSF flows through the subarachnoid space of the brain and
spinal cord.
• It is finally reabsorbed into the dural venous sinuses through arachnoid
granulations.

Cont…
• The organic constitutes are amino acids, sugar, proteins, cholesterol,
urea, uric acid and Creatinine.
• The inorganic constitutes are sodium, calcium, potassium,
magnesium, chlorides, bicarbonates and phosphates.
Clinical note:
1. Hydrocephalus: It is a condition of increased intracranial pressure
due to the defective absorption or circulation of CSF. Baby will
show enlargement of the cranial cavity and associated damage to
the brain because of pressure effect.
2. Lumbar puncture: It is a procedure by which CSF is taken out
from the subarachnoid space. Normally CSF is drawn by
introducing a needle between 3rd and 4th lumbar vertebrae.
Histological and biochemical study of CSF gives an indication
about various disease processes affecting CNS.

Functions of CSF:
• It acts as a cushion between the brain and rigid
cranium.
• Supports the weight of brain.
• Distributes force of blows on the head.
• Maintains intracranial pressure.
• It drains metabolites from the brain.
• It supplies nutrients and oxygen to the brain.

The Autonomic Nervous System:
• The peripheral nervous system consists of the somatic nervous system
(SNS) and the autonomic nervous system (ANS).
• The SNS consists of motor neurons that stimulate skeletal muscles.
• The ANS consists of motor neurons that control smooth muscles, cardiac
muscles, and glands.
• In addition, the ANS monitors visceral organs and blood vessels with
sensory neurons, which provide input information for the CNS.
• The ANS is further divided into the sympathetic nervous system and the
parasympathetic nervous system. Both of these systems can stimulate and
inhibit effectors.
• However, the two systems work in opposition—where one system
stimulates an organ, the other inhibits.

Organization of autonomic outflow:
• ANS consists of preganglionic and post ganglionic neurons.
• Cell bodies of preganglionic neurons are located in the lateral gray column
of spinal cord and motor nuclei of cranial nerve.
• Axons are myelinated and they synapse with cell bodies of post-ganglionic
neurons located outside CNS.
1. Sympathetic division: Sympathetic fibres arise from thoraco lumbar
regions.
 Axons of preganglionic sympathetic fibres leave spinal cord through
ventral route.
 They pass through white rami communicants to reach paravertebral
ganglion chains.
 In the ganglion, they make synaptic connections with cell bodies of
postganglionic neurons.
 Post ganglionic neuron pass through sympathetic nerves to reach the
viscera.

Cont…
2. Parasympathetic division: Parasympathetic
fibres come from cranio-sacral regions.
Preganglionic fibres end on short postganglionic
neurons present on or near the viscera.
• Cranial division supplies the visceral structures
of head, thorax and upper abdomen through
facial, glossopharyngeal and vagus nerves.
• Sacral division supplies pelvic branches of
sacral nerves.

Neurotransmitters in ANS
sympathetic fibres:
1. Preganglionic fibres ACETYLCHOLINE.
2. Postganglionic adrenergic fibres
ADRENALINE.
3. Postganglionic cholinergic fibres
ACETYLCHOLINE.
• Adrenaline and noradrenaline act through α, β1
and β2 receptors.

Parasympathetic fibres:
• Pre and postganglionic fibres- Acetylcholine.
• The neurotransmitters bring about the desired response by
acting on the respective receptors.
• Acetylcholine has 2 types of receptors namely:
1. Nicotinic receptors.
2. Muscarinic receptors.
• The drugs which produce effects similar to sympathetic and
parasympathetic stimulation are called sympathomimetic
and para-sympathomimetic drugs.
• Sympathetic and parasympathetic blockers prevent the
action of respective neurotransmitter at the target site by
blocking the receptors.

THE NERVOUS SYSTEM
SHORT ESSAY(Anatomy)
1. Name the parts of central nervous system and describe the cerebral
hemisphere
2. Name the various lobes of cerebrum. Describe various functional areas of
cerebrum
3. Explain the structure of cerebellum in detail
4. Describe brachial plexus of nerves
5. Spinal cord
6. Draw a neat labeled diagram of circle of Willis
7. Trochlear nerve
8. Explain cerebellum with its anatomical significance.
9. Classify nervous system and write a note on neurons
10. Ulnar nerve and its applied anatomy
11. Radial nerve and its applied anatomy

SHORT ANSWERS
1. Name the parts of the brain stem
2. Name ventricles of brain
3. Name major parts of central nervous system
4. Mention the functions of CSF
5. Name 4 cranial nerves
6. Mention the two functions of cerebellum
7. Spinal ganglion
8. What is wry neck
9. Erb’s palsy
10. Carpal tunnel syndrome
11. Mention 2 parts of sciatic nerve
12. Neuralgia
13. Bell’s palsy
14. Lumbar puncture
15. Name the branches of the trigeminal nerve
16. Mention the function of hypoglossal nerve
17. Explain the deformity in klumpke’s paralysis
18. Special features of Medulla oblongata
19. Draw a labeled diagram of neurons.
20. Mention the parts of the brain
21. List the cranial nerves.
22. Name the parts of central nervous system
23. Name the meningeal coverings of brain in order.

SHORT ESSAYS (Physiology):
1. Describe the mechanism of impulse transmission through
the nerve fibers.
2. Explain the transmission of nerve impulses through a
synapse.
3. Describe the properties of nerve fibers.
4. Discuss the properties of a synapse.
5. Explain the function of synapse with a neat labeled
diagram.
6. Discuss the structure of Neurons with its functions
7. Describe neuron and add a note on salutatory conduction
of nerve impulses.
8. Describe Neuroglia and its functions.
9. Explain the functional areas of Cerebrum
10.Describe the functions of cerebellum
11.Explain the functions of Hypothalamus.

12.Explain the functions of Medulla Oblongata.
13.Enumerate the cranial nerves and its functions.
14.Discuss the functions of Spinal nerves
15.Explain the functions of Sympathetic Nervous System.
16.Explain the functions of Para Sympathetic Nervous System
17.Illustrate the mechanism of reflex action through a Reflex Arch.
18.Describe neuromuscular junction with a neat labeled diagram.
19.Enumerate the composition and functions of CSF
20.Describe the circulation of CSF in detail.
21.Explain Reflex and its types in detail.
22.Explain the types of pain with examples.
23.Describe automatic learning and its application.
24.Explain Biofeedback and its applications.

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