neurones central nervous system brain spinal cord peripheral nervous system spinal nerves cranial nervous

2. • The nervous system consist of the brain, the spinal
cord, and peripheral nerves. The structure and
organization of the tissues that form these
components enables rapid communication between
different parts of the body.
• Response to changes in the internal environment
regulates essential involuntary functions, such as
respiration and blood pressure. Response to changes
in the external environment maintains posture and
other voluntary activities.

3. PARTS OF NERVOUS SYSTEM
• The central nervous system (CNS) consisting of the brain and
spinal cord.
• The peripheral nervous system(PNS) consisting of all the nerves
outside the brain and spinal cord.
• The PNS comprises of paired and sacral nerves some of these are
sensory (afferent) some are motor (efferent) some are mixed. It is
useful to consider two functional parts within the PNS.
• The sensory division
• The motor division

4. The motor division is involved in
• Voluntary- the somatic nervous system (movement
of voluntary muscles).
• Involuntary- the autonomic nervous system
(functioning of smooth and cardiac muscle glands).
The autonomic nervous system has two divisions:
sympathetic and parasympathetic.

5. • The nervous system consist of neurons, which
conduct nerve impulses and are supported by unique
connective tissue cells known as neuroglia. There are
vast number of cells. The body has billions of nerve
cells or neurons.

6. NEURONES
• Each neurons consist of a cell body and its
processes. One axon and many dendrites, neurons
are commonly referred as nerve cells.
• Bundles of axons bound together are called nerves.
• Neurons cannot divide, they can synthesize chemical
energy (ATP) only from glucose.
• Neurons generate and transmit electrical potentials.

8. Nerve impulses can be initiated in response
to stimuli from:-
• Outside the body- light, touch
• Inside the body- a change in the concentration of
carbon dioxide in the blood alters respiration

9. Cell bodies
• Also known as soma
• Too small to be seen by naked eyes
• Cell bodies form gray matter of the nervous system
and found on the periphery of the brain and in the
center of the spinal cord
• Groups of cell bodies are called nuclei in the CNS
and ganglia in the PNS.
• An exception is basal ganglia (nuclei) within the
cerebrum.

10. AXON AND DENDRITES
• Axon and dendrites are extension of cell bodies and
form white matter of the nervous system
• Axon are found deep in the brain and in groups
called tracts, at the periphery of the spinal cord
• They referred as nerves or nerves fibers outside the
brain and spinal cord

11. AXONS
• Each nerve cell has one axon which begins at a
tapered area of the cell body the axon hillocks.
• They carry impulses away from the cell body and are
usually longer than the dendrites , as long as 100cm.

12. STRUCTURE OF AN AXON
• The membrane of axon is called axolemma.
• It encloses the cytoplasmic extension of the cell
body.

13. Myelinated neuron
• Large axon & those of peripheral nerves are surrounded
by a myelin sheath
• This consists of series of Schwann cells arranged along
with the length of axon.
• Each one is wrapped around the axon so that it is
covered by number of concentric layers of Schwann
cells plasma membrane.
• Between these layers of plasma membrane there is a
small amount of fatty substance called myelin.

15. • The outermost layer of Schwann cell plasma
membrane is the neurilemma.
• There are tiny areas of exposed axolemma between
adjacent Schwann cells, nodes of Ranvier, which
assist the rapid transmission of nerve impulses in
Myelinated neurons.

16. Non- Myelinated neurons
• Postganglionic fibers and some small fibers in the
CNS are non-Myelinated.
• In this type a number of axons are embedded in
Schwann cells are in close association and there is no
exposed axolemma.
• The speed of transmission of nerve impulses is
slower.

17. DENDRITES
• These are many short processes that receive and
carry nerve impulses toward cell bodies.
• They have same structure as axon but usually shorter
and branching.
• In motor neurons dendrites forms part of synapse.
• In sensory neurons they form the sensory receptors
that respond to specific stimuli.

18. THE NERVE IMPULSES (ACTION
POTENTIAL)
• An impulse is initiated by stimulation of sensory
nerve endings or by passage of an impulse from
another nerve.
• Transmission of the impulse or action potential is
due to movement of ions across the nerve cell
membrane.
• There is a different electrical charge on each side of
the membrane, which is known as membrane
potential.

19. • In the resting state the nerve cell membrane is
polarised i.e. outside there is positive charge and
inside its negative charge. The principle ions
involved in is:-
• Sodium main (Na+) extracellular cation
• Potassium (K+) intracellular cation

22. DEPOLARIZATION
• Na+ floods into neuron from the extracellular fluid
to intracellular fluids causing depolarization,
creating a nerve impulse or action potential.
• It is very rapid enabling the conduction of a nerve
impulse along the entire length of a neuron in a few
milliseconds.
• It passes from area of stimulation to resting potential,
it takes time for repolarization to occur.

24. The synapse and neurotransmitters
• There is always more than one neuron is involved in the
transmission of a nerve impulses from its origin to its
destination, whether its sensory or motor.
• No physical contact between these neurones.
• The point at which the nerve impulse passes from one to
another is synapse.

25. • At its free ends the axon of the presynaptic neurone
breaks up into minute branches that terminate into small
swellings called synaptic knobs or terminal buttons.
• These are in close proximity to the dendrites and the cell
body of postsynaptic neuron.
• The space between them is synaptic cleft.
• Synaptic knobs contain spherical vesicles, synaptical
vesicles, in which neurotransmitters are stored.

27. • These chemical are synthesized by nerve cells, actively
transported along the axons and stored in vesicles.
• They are released by exocytosis in response to action
potential and diffuse across the synaptic cleft.
• They act on the specific receptor site on the postsynaptic
membrane. There action is short lived as they acted on
effector organ or neurone, taken up by synaptic knob.

28. NERVES
• A nerve consists of numerous neurones collected into
bundles (bundles of nerve fibers in the CNS known as
tract) . each bundle have several covering of connective
tissue
1. Endonerium- surrounding the individual fiber.
2. Perineurium- smooth connective tissue surrounding
each bundle of fibers.
3. Epineurium- is the fibrous tissue which surrounds and
encloses a number of bundles of nerve fibers .

30. Sensory or afferent nerves
• Sensory nerves carry information from the body to
the spinal cord.
• And then information pass to brain or to connector
neuron of reflex arc in the spinal cord.

32. Sensory receptors
• Specialized endings respond to different stimuli inside
and outside the body
1. Somatic, cutaneous or common senses- these originate
in the skin, they are pain, touch, heat and cold , sensory
nerve ending in the skin are fine branching filaments
without myelin sheaths. When stimulated an impulse is
generated and transmitted by the sensory nerves to the
brain where sensation is perceived.

33. 2. Proprioceptor senses- these originates in the muscles and
joints and contribute to the maintenance of balance and
posture.
3. Special senses- These are sight, hearing, balance, smell and
taste.
4. Autonomic afferent nerves- These originates in the internal
organs, glands, and tissues e.g.- baroreceptors involved in
control of blood pressure., chemoreceptors involved in control
of respiration .

34. Motor or efferent nerves
• Motor nerves originates in the brain, spinal cord and
autonomic ganglia.
• They transmit impulses to the effector organs ; muscles
and glands there are two types-
1. Somatic nerve- Involved in involuntary and reflex
skeletal muscle contraction.
2. Autonomic nerves- (Sympathetic of parasympathetic)
involved in cardiac and smooth muscle contraction and
glandular secretions.

35. MIXED NERVES
• In the spinal cord, sensory and motor nerves are
arranged in separate groups or tracts.
• Outside the spinal cord, when sensory and motor
nerves are enclosed within same sheath of
connective tissue they are called mixed nerves.

36. NEUROGLIA
• The neurones of the CNS are supported by four types
of non- excitable glial cells
• Unlike the nerve cell which cannot divide glial cell
continue to replicate throughout life
1. Astrocytes
2. Oligodendrocytes
3. Ependymal cells
4. microglia

37. ASTROCYTES
• Main supporting tissue of CNS
• Star shaped with fine branching
• At the free end of some of the processes are small
swellings called foot processes.
• Found in large number adjacent to blood vessels with
their foot processes forming a sleeve around them
• This means blood is separated from the neurones by
the capillary wall and a layer of foot processes
together constitute the blood brain barrier.

38. Blood brain barrier
• That protect the brain from potentially harmful toxic
substances and chemical variations in the blood e.g. after a
meal.

39. OLIGODENDROCYTE
• These cells are smaller than astrocytes.
• Found in clusters round nerve cell bodies in grey
matter, where they have supporting function along
the length of Myelinated neuron.
• They form and maintain myelin.

40. EPENDYMAL CELLS
• These cells form the epithelial lining of the
ventricles of the brain and the central canal of the
spinal cord
• Those cells that form choroid plexuses (a network of
blood vessels that secret CSF in ventricles) of the
ventricles secret CSF.

41. MIRCOGLIA
• These derived from monocytes.
• Migrate from the blood into nervous system before birth.
• Found mainly in areas of blood vessels
• In area of inflammation and cell destruction they become large
and phagocytic to remove microbes and damaged tissue.

42. CNS ( The meninges and CSF)
THE MENINGES
• The brain and spinal cord are completely
surrounded by 3 layers of tissue, the meninges
lying between skull and the brain and between the
vertebral foramina and spinal cord.
1. Dura matter
2. Arachnoid matter
3. Pia matter

44. DURA MATTER
• It consist of two layers of dense fibrous tissue.
• The outer layer takes the place of the periosteum of
the skull bones
• Inner layer provide protection to brain.
• Inner layer sweeps inward between two cerebral
hemispheres forming falx cerebri and between the
cerebrum and cerebellum to form tentorium
cerebelli.

45. Arachnoid matter
• This is a layer of fibrous tissue that lies between the
Dura and Pia matter
• Middle layer
• Separated from the Dura matter by the subdural
space , and from the Pia matter by subarachnoid
space , containing CSF.
• It continue downward to envelop the spinal cord
and ends by merging with Dura matter at level of
sacral vertebra.

46. Pia matter
• Inner layer
• Delicate layer of connective tissue containing many
minute blood vessels
• It adhere to the brain
• Continue downward surrounding the spinal cord
• At end of spinal cord it continue as filum terminale

47. • The Dura and arachnoid matter separated by a
potential space, the subdural space.
• The arachnoid and Pia matter are separated by the
subarachnoid space, containing CSF.

48. Ventricles of the brain and CSF
• The brain contains four irregular shaped cavities or
ventricles, contains CSF . They are
1. Right or left lateral ventricle
2. Third ventricle
3. Fourth ventricle

50. • These cavities lies within the cerebral hemisphere,
one on each side of the median plane.
• They are separated by a thin membrane, the septum
lucidum
• Lined with ciliated epithelium
• Communicate with the third ventricle by
interventricular foramina
The lateral ventricle

51. The third ventricles
• Cavity situated below the lateral ventricles between
the two parts of thalamus
• Communicate with the fourth ventricle by cerebral
aqueduct

52. Fourth ventricle
• Diamond shaped cavity
• Below and behind the third ventricle
• Between cerebellum and pons
• Continue with the central canal of the spinal cord
and communicate with subarachnoid space.

54. • CSF is secreted into each ventricle by choroid
plexuses.
• The movement of CSF from the subarachnoid space
to vinous sinuses depends upon the pressure on
each side of the walls of arachnoid villi.
• When CSF pressure is higher than venous pressure
fluid passes into blood
• When venous pressure is high arachnoid villi
collapse, preventing blood constituent into CSF

55. • CSF is secreted continously at the rate of about 0.5 ml /
min i.e. 720 ml per day.
• CSF is clear, slightly alkaline fluid with a specific gravity
of 1.005.
• CSF is consist of;-
1. Water
2. Mineral salts
3. Glucose
4. Plasma proteins
5. Creatinine and urea in small amount
6. a few leukocytes

56. FUNCTIONS OF CSF
• Supports and protects the brain and spinal cord by
maintaining a uniform pressure around these
structures
• Function as cushion or shock absorber between the
brain and the skull.
• Keeps brain and spinal cord moist
• Exchange of nutrients and waste products between
CSF and nerve cells.

57. BRAIN
• The brain constituents about one fifth of the body
weight and lies within the cranial cavity, the parts are
Cerebrum
Thalamus
Hypothalamus
Midbrain
Pons
Medulla oblongata
cerebellum

59. Blood supply to the brain
• Blood supply to the brain is normally divided into
anterior and posterior segments, relating to the
different arteries that supply the brain. The two main
pairs of arteries are the Internal carotid arteries
(supply the anterior brain) and vertebral arteries
(supplying the brainstem and posterior brain).

60. Cerebrum
• Largest part of the brain
• Occupies the anterior and middle cranial fossae
• Divided into left and right hemisphere by deep
longitudinal cerebral fissure each containing
ventricles.
• Deep with in the brain the hemisphere is connected
by a mass of white matter known as corpus
callosum.

62. • The superficial layer of cerebrum is composed of nerve cell
bodies or grey matter forming cerebral cortex and deeper
layer consist of white matter.
• Cerebral cortex contains various folds, the exposed area of
folds are gyri and these are separated by sulci.
• For descriptive purpose cerebrum is divides into lobes
1. Frontal
2. Temporal
3. Parietal
4. occipital

64. CEREBRAL TRACTS AND BASAL GANGLIA
• The surface of the cerebral cortex is composed of grey
matter
• Within the cerebrum the lobes are connected by a masses of
nerve fibers, tracts, which makes up the white matter of the
brain.
• The internal capsule is important projection tracts that lies
deep within the brain between basal ganglia and thalamus.

65. BASAL GANGLIA
• Deep within the hemisphere are group of cell bodies
called nuclei.
• They act as a relay station with connection to many parts
of including motor areas of cerebral cortex and thalamus
• Their functions include initiation and fine control of
complex movement and learned coordinated activities
such as posture and walking.
• If control is inadequate or absent movements are jerky,
clumsy and uncoordinated.

66. Functions of cerebral cortex
1. Mental activities-
• involved in memory
• Intelligence
• sense of responsibility
• Thinking
• Reasoning
• Moral sense
• Learning

67. 2. Sensory perception-
• Perception of pain
• Temperature
• Touch
• Sight
• Hearing
• Taste and smell
3. Initiation and control of skeletal muscle
contraction and therefore voluntary movement.

68. Motor areas of cerebral cortex
• Primary motor area-
• This lies in the frontal lobe immediately anterior to the central sulcus
• The cell bodies id pyramid shaped (betz’s cells) and control skeletal
muscle activities.
• There are two neurone involved in the pathway to skeletal muscle- the
first ( upper motor neurone) descend from the motor cortex through
the internal capsule to the medulla oblongata.

70. • And crosses to the opposite site and descend in the
spinal cord
• It synapse with second neurone (lower motor neurone)
which leaves the spinal cord and travel to target muscle
• This means that motor area of right hemisphere control
the voluntary muscle movement on the left side of the
body.
• In motor area of the cerebrum the body represented
upside down i.e. the uppermost cells control the feet and
those of lowest part control the head, face and fingers.

72. BROCA’S AREA (MOTOR SPEECH AREA)
• This is situated in the frontal lobe just above the
lateral sulcus
• Controls the muscle movements needed for speech

73. SENSORY AREAS OF CEREBRAL CORTEX
THE SOMATOSENSORY AREA-
 Behind the central sulcus
 Sensation of pain, temp, pressure and touch,
awareness of muscular movement and the position
of joints.
 Right hemisphere control the left side and vice
versa.
 Face has large nerve extensive area by three
branches of trigeminal nerve (5th cranial nerve)

74. Auditory area-
• Lies below the lateral sulcus within temporal lobe
• The nerve cell receive and interpret impulses
transmitted from the inner ear by the cochlear
(auditory) part of vestibulo-cochlear nerve (8th
nerve)

75. OLFACTORY AREA-
• Lies deep within the temporal lobe
• where impulses from the nose, transmitted via the
olfactory nerve (1st cranial nerve) are receive and
interpreted.
TASTE AREA-
• Lies just above the lateral sulcus in the deep layers
of somatosensory area.
• Impulses from sensory receptors in the taste buds
are received and perceived as taste.

76. The visual area-
• Lies behind the parito-occipital sulcus and includes
the greater part of occipital lobe
• The optic nerve (2nd cranial nerve) pass from the eye
to this area which receive and interprets the
impulses as visual impressions.

77. THALAMUS
• Consists of two masses of grey and white matter.
• Situated within the cerebral hemispheres just below
the corpus callosum one on each side of third
ventricle.
• Sensory receptors in the skin and viscera send
information about touch, pain and temp, and input
from special sense organs travel to the thalamus.

79. HYPOTHALAMUS
• Small but important structure which weigh around 7g and
consist of a number of nuclei.
• Situated below and in front of thalamus, immediately
above the pituitary gland .
• Hypothalamus is linked to the posterior lobe of pituitary
gland by nerve fibers and to the anterior lobe by a
complex system of blood vessels

80. • The hypothalamus controls the output of hormones from
both lobes of pituitary gland and other function are
control of-
1. The autonomic nervous system
2. Appetite and satiety
3. Thirst and water balance
4. Body temperature
5. Emotional reactions e.g.- pleasure, fear and rage
6. Sexual behavior and child rearing
7. Sleeping and waking cycle

81. BRAIN STEM (MIDBRAIN)
• Midbrain is the brain situated around the cerebral
aqueduct between the cerebrum above and the pons
below.
• Consists of nuclei and nerve fibers, which connect the
cerebrum with lower parts of the brain and the spinal
cord.
• Act as a relay station for the ascending and descending
nerve fibers.

82. PONS
• Situated in front of the cerebellum below the midbrain
and above the medulla oblongata.
• It consist of mainly nerve fibers (white matter) that form
a bridge between the two hemispheres of the
cerebellum, and of fibers passing between the higher
level of brain and spinal cord.

83. • Acts as a relay center and some of these associated
with cranial nerves.
• Other form the pneumotaxic center and apneustic
center that operate in conjunction with respiratory
center in the medulla oblongata.

84. MEDULLA OBLONGATA
• It extends from the pons above and continuous with
the spinal cord.
• 2.5 cm long and lies in the cranium.
• The outer aspect is composed of white matter which
passes between the brain and spinal cord.
• Grey matter centrally.

85. • The vital centers consisting of groups of cell bodies
associated with autonomic reflex activity lie in
deeper structure. These are-
1. Cardiovascular center- controls the rate and force
of cardiac contraction and also control blood
pressure.
2. Respiratory center
3. Reflex center for vomiting, coughing, sneezing and
swallowing.

86. RETICULAR FORMATION
• Collection of neurone in the core of the brain stem,
surrounded by neural pathway that conduct
ascending and descending nerve impulses between
brain and spinal cord.
• It has vast number of synaptic link with other parts
of brain therefore constantly receiving information
being transmitted in ascending and descending tracts.

87. FUNCTIONS-
Coordination of skeletal muscle activity (voluntary
motor movement) and maintenance of balance.
Coordination of autonomic nervous system activity
e.g.- CVS, respiratory and GI activity.
Selective awareness that function through the reticular
activating system , which selectively block or passes
sensory information to the cerebral cortex. E.g.- slight
sound made by sick child may arouse his mother but
noise of train does not disturb her.

88. CEREBELLUM
• Situated behind the pons and below the posterior
portion of the cerebrum, occupying posterior cranial
fossae.
• Ovoid in shape with two hemispheres, separated by a
narrow median strip. Called vermis
• Grey matter form the surface of cerebellum
• White matter lies deeply.

89. FUNCTIONS OF CEREBELLUM-
Concerned with voluntary muscle movement,
posture and balance.
Receive information from sensory system , the spinal
cord and other parts of brain and then regulate motor
movement.
Coordination and speech resulting in smooth and
balanced muscular activity.

90. SPINAL CORD
• Cylindrical part of CNS surrounded by meninges.
• Continuous above with medulla and extend from the
upper border of atlas to the lower boarder of 1st lumber
vertebra.
• 45cm long
• Spinal cord is incompletely divided into two parts
anteriorly by a short, shallow median fissure and
posteriorly by deep narrow septum posterior median
fissure.
• Composed of grey matter in center surrounded by
white matter.

93. GREY MATTER
• The arrangement of grey mater resembles letter H,
having two posterior, two anterior and two lateral
columns.
• The nerve cell bodies may be
• Sensory neurones which receive impulses from
periphery of the body.
• Lower motor neurones, which transmit impulses to
skeletal muscles.
• Connector neurone (interneuron) linking sensory and
motor neurone, which form reflex arc.

94. Posterior columns of grey matter-
• These are composed of cell bodies that are stimulated
by sensory impulses from the periphery of the body.
• The nerve fibers contribute to the formation of white
matter and transmit the sensory impulses upward to
brain.

95. Anterior columns of grey matter-
• These are composed of the cell bodies of the lower
motor neurones that are stimulated by the upper motor
neurone or the connector neurone linking the anterior
and posterior columns to from reflex arc.

96. WHITE MATTER
• Arranged in three columns or tracts, anterior,
posterior and lateral.
• These tracts are formed by sensory nerve fibers
ascending to the brain, motor nerve fibers
descending from the brain and fibers of connector
neurone.
• Tracts are named according to their points of origin
and destination e.g.- spinothalamic and
corticospinal.

97. Sensory nerve tracts in the spinal cord
There are two main sources of sensation transmitted to
brain via spinal cord.
1. THE SKIN-
• Sensory receptors in the skin called cutaneous
receptors, are stimulated by pain, heat, cold and touch,
including pressure.
• Nerve impulses are generated are conducted by three
neurone to the sensory are in the opposite hemisphere
of the cerebrum where sensation are perceived.

98. 2. THE TENDONS, MUSCLES AND JOINTS-
• Sensory receptors are specialized nerve ending in
these structures called proprioceptors and stimulated
by stretch.
• Together with the impulses from eye and ear they are
associated with maintenance of balance and posture
and with perception of the position of the body .
These nerve impulses have two destinations-

99. • By a three neurone system- the impulses reach the
sensory area of opposite hemisphere of the
cerebrum.
• By a two neurone system- the nerve impulses reach
the cerebellar hemisphere on the same side

100. Motor nerve tracts in spinal cord
• Motor neurones stimulation results in-
1. Contraction of skeletal (voluntary) muscles.
2. Contraction of smooth (involuntary) muscles,
cardiac and secretion by glands controlled by
nerves of autonomic nervous system.

101. Voluntary muscle movement
• Efferent nerve impulses are transmitted from the
brain to other parts of body via bundles of nerve
fibers in the spinal cord.
• The motor pathway from the brain to the muscles
are made up of two neurones , these pathways are-
1. Pyramidal (corticospinal)
2. extrapyramidal

102. The upper motor neurone
• This has its cell body in the primary motor area of the
cerebrum.
• The axon pass through the internal capsule pons and
medulla.
• In the spinal cord they form the lateral corticospinal tracts
of white matter and the fibers synapse with cell bodies of
lower motor neurone in the anterior columns of grey
matter.
• The axon of the upper motor neurone make up the
pyramidal tracts and decussate in the medulla forming the
pyramid.

104. Lower motor neurone
• Near its termination in skeletal muscle the axon branches
into many tiny fibers each of which is in close association
with a sensitive area on the wall of a muscle fibers known
as a motor end plate.
• The lower motor neurone is the final common pathway
for the transmission of nerve impulses to skeletal
muscles.

105. • The outcome of these influences is smooth,
coordinated muscle movements. Some of which is
voluntary and involuntary.

106. Involuntary muscle movements
Upper motor neurones-
• These have their cell bodies in the brain at a level
below the cerebrum i.e. in the midbrain, brainstem,
cerebellum or spinal cord.
• They influences muscle activity that maintain
posture and balance, coordinates skeletal muscle
movement and controls muscle tone.

107. SPINAL REFLEXES-
• Sensory neurones
• Connector neurones
• Lower motor neurones

108. Stretch reflexes-
• Only two neurones are involved.
• Cell body of lower motor neurone is stimulated
directly by the sensory neurone with no connector
neurone in between. E.g.- knee jerk reflex .
• By tapping the knee this stimulate nerve impulses and
passes to spinal cord to the cell body of the lower
motor neurone in the anterior column of grey matter
and result in forward kicking of foot.

109. AUTONOMIC REFLEX-
• It include pupillary reflex.
• When pupil immediately constrict in response to
bright light, preventing retinal damage.

110. PERIPHERAL NERVOUS SYSTEM
This part of the nervous system consist of-
31 pairs of spinal nerves
12 pairs of cranial nerves
The autonomic nervous system

111. SPINAL NERVES
They are named according to the vertebra with which
they are associated-
8 cervical
12 thoracic
5 lumber
5 sacral
1 coccygeal

112. • The lumber, sacral and coccygeal nerve leaves the
spinal cord near its termination at the level of 1st lumber
vertebra and extend downwards inside the vertebral
canal in subarachnoid space forming a sheet of nerve
which resembles a horse tail, the cauda equina.

114. NERVE ROOTS
• The spinal nerve arise from both side of the spinal cord
• Each nerve is formed from union of a motor (anterior)
and sensory (posterior) nerve root and Is therefore a
mixed nerve.
• The anterior nerve root consist of motor nerve fibers
which are the axon of the lower motor neurone from the
anterior column of the grey matter in the spinal cord
• and in thoracic and lumber region, sympathetic nerve
fibers which are axon of cells in the lateral column of
grey matter.

115. • The posterior nerve root consist of the sensory
nerve fibers .
• Just outside the spinal cord there is spinal ganglion
(posterior or dorsal root ganglion) consisting of a
cluster of cell bodies.
• Sensory nerve fibers pass through thee ganglion
before entering the spinal cord.
• The area of skin whose sensory receptors contribute
to each nerve is called dermatome.

117. BRANCHES
• Immediately after emerging from the intervertebral
foramen spinal nerve divide into branches or rami
• A posterior and a anterior rami
• The rami communicante are part of preganglionic
sympathetic neurones of autonomic nervous system.

118. • The posterior rami pass backward and divide into
smaller medial and lateral branches to supply skin
and muscles of relatively small areas of posterior
aspect of the head, neck and trunk
• The anterior rami supply the anterior and lateral
aspects of the neck and the upper and lower limbs.

119. PLEXUSES
• In the cervical, lumber and sacral regions the anterior
rami unite near their origin to form large masses of
nerves or plexuses
• Where nerve fibers are regrouped and rearranged before
proceeding to supply skin, bones, muscles and joints of
a particular area.
• this means that these structures have a nerve supply
more than one spinal nerve and therefore damage to one
spinal nerve does not cause loss of function of regions

120. • There are five large plexuses of mixed nerves formed
on each side of the vertebral column. They are-
1. Cervical plexuses
2. Brachial plexuses
3. Lumber plexuses
4. Sacral plexuses
5. Coccygeal plexuses.