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1. SPINAL CORD AND SPINAL NERVES
Ravish Yadav

2. SPINAL CORD AND SPINAL NERVES
• Contribute to homeostasis
• Providing quick, reflexive responses to
many stimuli.
• The spinal cord is the pathway for sensory
input to the brain and motor output from
the brain.

3. PROTECTIVE STRUCTURES
Two types of coverings:-
• Bony vertebrae
• Connective tissue meninges
• Plus a cushion of cerebrospinal fluid surround and protect the delicate
nervous tissue of the spinal cord.
Vertebral Column:-
• The spinal cord is located within the vertebral canal of the vertebral
column.
• Provide a sturdy shelter for the enclosed spinal cord.

4. Meninges:-
• The spinal meninges are three connective tissue coverings surround the
spinal cord.
• Superficial is the dura mater, it continuous with the dura mater of the brain,
to the second sacral vertebra.
• Middle is the arachnoid mater, It is deep to the dura mater and is continuous
with the arachnoid mater of the brain.
• Between the dura mater and the arachnoid mater is a thin subdural space,
which contains interstitial fluid.
• The innermost is the pia mater that adheres to the surface of the spinal cord.
• Within the pia mater are many blood vessels that supply oxygen and
nutrients to the spinal cord.
• Between the arachnoid mater and the pia mater is the subarachnoid space,
which contains cerebrospinal fluid.

6. EXTERNAL ANATOMY OF THE SPINAL CORD
• Cylindrical , elongated.
• Extends from the medulla oblongata to the superior border of the second
lumbar vertebra.
• Approximately 45 cm long ; diameter is about 2 cm.
• Diameter somewhat larger in the lower cervical and midlumbar regions, and
smallest at the inferior tip.
• The cervical enlargement, extends from the fourth cervical vertebra to the
first thoracic vertebra.
• The lumbar enlargement, extends from the ninth to the twelfth thoracic
vertebra.

8. • Terminates as a tapering, conical structure called the conus medullaris.
• Arising from the conus medullaris is the filum terminale, that anchors the
spinal cord to the coccyx.
• The spinal cord is shorter than the vertebral column, nerves that arise from
the lumbar, sacral, and coccygeal regions of the spinal cord do not leave the
vertebral column at the same level they exit the cord.
• The end of the spinal cord like wisps of hair due to roots of nerves.
• Appropriately, the roots of these nerves are collectively named the cauda
equina meaning “horse’s tail”

10. SPINAL NERVES
• The paths of communication between the spinal cord and specific regions of
the body.
• The 31 pairs of spinal nerves emerge at regular intervals from intervertebral
foramina.
• The naming of spinal nerves is based on the segment in which they are
located.
• There are :-
• 8 pairs of cervical nerves (C1–C8)
• 12 pairs of thoracic nerves (T1–T12)
• 5 pairs of lumbar nerves (L1–L5)
• 5 pairs of sacral nerves (S1–S5)
• 1 pair of coccygeal nerves (Co1).

12. • Two bundles of axons, called roots, connect each spinal nerve to a segment of
the cord by even smaller bundles of axons called rootlets.
• The posterior (dorsal) root and rootlets contain only sensory axons.
• Each posterior root has a swelling, the posterior (dorsal) root ganglion, which
contains the cell bodies of sensory neurons.
• The anterior (ventral) root and rootlets contain axons of motor neurons.

14. INTERNAL ANATOMY OF THE SPINAL CORD
• Consist regions of white matter that surround an inner core of gray matter.
• Consists bundles of myelinated axons of neurons.
• Anterior median fissure and Posterior median sulcus are penetrate the
white matter of the spinal cord and divide it into right and left sides.
• The gray matter shaped like letter H or butterfly.
• Consists of dendrites and cell bodies of neurons, unmyelinated axons, and
neuroglia.
• Center of the gray commissure is a small space called the central canal.
• Anterior (ventral) white commissure, which connects the white matter of
the right and left sides of the spinal cord.

15. GRAY MATTER IN SPINAL CORD
• The gray matter on each side is subdivided into regions called horns.
• The posterior (dorsal) gray horns contain cell bodies and axons of
interneurons as well as axons of incoming sensory neurons.
• The anterior (ventral) gray horns contain somatic motor nuclei, that provide
nerve impulses for contraction of skeletal muscles.
• Between the posterior and anterior gray horns are the lateral gray horns
contain autonomic motor nuclei, which are autonomic motor neurons that
regulate the activity of cardiac muscle, smooth muscle, and glands.

17. WHITE MATTER IN SPINAL CORD
• The gray horns divide the white matter on each side into three broad areas
called columns:
• (1) Anterior (ventral) white columns, (2) Posterior (dorsal) white columns,
and (3) Lateral white columns.
• Each column in contains distinct bundles of axons, which may extend long
distances up or down the spinal cord, are called tracts.
• Tracts are bundles of axons in the CNS, whereas nerves are bundles of axons
in the PNS.
• Sensory (ascending) tracts consist of axons that conduct nerve impulses
toward the brain.
• Tracts consisting of axons that carry nerve impulses from the brain are called
motor (descending) tracts.
• Sensory and motor tracts of the spinal cord are continuous with sensory and
motor tracts in the brain.
• Tracts are often named according to their points of origin and destination,
e.g. spinothalamic, corticospinal

19. SENSORY NERVE TRACTS (AFFERENT OR
ASCENDING) IN THE SPINAL CORD
• There are two main sources of sensation transmitted to the brain via the
spinal cord.
1. The skin.
• Sensory receptors (nerve endings) in the skin, called cutaneous receptors, are
stimulated by pain, heat, cold and touch, including pressure.
• Nerve impulses generated are conducted by three neurones to the sensory area in
the opposite hemisphere of the cerebrum where the sensation and its location are
perceived.
• Crossing to the other side, or decussation, occurs either at the level of entry into
the cord or in the medulla.

21. 2. The tendons, muscles and joints.
• Sensory receptors are nerve endings in these structures, called proprioceptors, and
they are stimulated by stretch.
• Together with impulses from the eyes and the ears they are associated with the
maintenance of balance and posture and with perception of the position of the body
in space.
• These nerve impulses have two destinations:
• By a three-neurone system the impulses reach the sensory area of the opposite
hemisphere of the cerebrum
• By a two-neurone system the nerve impulses reach the cerebellar hemisphere on the
same side.

22. MOTOR NERVE TRACTS (EFFERENT OR
DESCENDING) IN THE SPINAL CORD
• Neurones which transmit nerve impulses away from the brain are motor
(efferent or descending) neurones.
• Motor neurone stimulation results in:
•Contraction of skeletal (striated, voluntary) muscle
•Contraction of smooth (involuntary) muscle, cardiac muscle and the secretion by
glands controlled by nerves of the autonomic nervous system

23. VOLUNTARY MUSCLE MOVEMENT
• The contraction of the muscles is under conscious (voluntary) control,
• That originates at the level of consciousness in the cerebrum.
• Some nerve impulses which affect skeletal muscle contraction are
• Initiated in the midbrain, brain stem and cerebellum.
• This involuntary activity is associated with coordination of muscle activity,
• E.G. when very fine movement is required and in the maintenance of posture and
balance.
• Efferent nerve impulses are transmitted from the brain to the body via
bundles of nerve fibres or tracts in the spinal cord.
• The motor pathways from the brain to the muscles.

24. THE UPPER MOTOR NEURONE
• This has its cell body (Betz‘s cell) in the precentral sulcus area of the
cerebrum.
• The axons pass through the internal capsule, pons and medulla.
• In the spinal cord
• They form the lateral corticospinal tracts of white matter and the fibres terminate in
the cell bodies of the lower motor neurones in the anterior columns of grey matter.
• The axons of these upper motor neurones decussate in the medulla
oblongata.

26. THE LOWER MOTOR NEURONE
• This has its cell body in the anterior horn of grey matter in the spinal cord.
• Its axon emerges from the spinal cord by the anterior root, joins with the
incoming sensory fibres and forms the mixed spinal nerve which passes
through the intervertebral foramen.
• Near its termination in muscle the axon branches into a variable number of
tiny fibres which form motor end-plates.
• The motor end-plates of each nerve and the muscle fibres they supply form
a motor unit.
• The neurotransmitter that conveys the nerve impulse across the synapse to
stimulate the muscle fibre is acetylcholine.
• Motor units contraction of a muscle depends on the number of motor units
in action at a time.

27. INVOLUNTARY MUSCLE MOVEMENT
Upper motor neurones:-
• These have their cell bodies in the brain at a level below the cerebrum,
• i.e. in the midbrain, brain stem, cerebellum or spinal cord.
• They influence muscle activity in relation to
• The maintenance of posture and balance, the coordination of muscle movement and the control of
muscle tone.

28. Reflexes and Reflex Arcs
• The second way
• The spinal cord promotes homeostasis is
• by serving as an integrating center for some reflexes.
• A reflex is
• A fast, automatic, unplanned sequence of actions
• That occurs in response to a particular stimulus.
• Some reflexes are
• Inborn and other reflexes are learned or acquired.
• When integration takes place in the spinal cord gray matter, the reflex is a
spinal reflex.
• Various types of reflexes like cranial reflex , somatic reflexes, autonomic
(visceral) reflexes etc.

29. REFLEX ARC
• Nerve impulses propagating into, through, and out of the CNS follow
specific pathways, depending on the kind of information, its origin, and its
destination.
• The pathway followed by nerve impulses that produce a reflex is a reflex
arc.
• A reflex arc includes the following five functional components:-
1. Sensory receptor.
2. Sensory neuron
3. Integrating center
4. Motor neuron
5. Effector

30. 1 Sensory receptor.
• The distal end of a sensory neuron (dendrite) serves as a sensory receptor.
• It responds to a specific stimulus by producing a graded potential.
• If a potential reaches the threshold level of depolarization, it will trigger one or more
nerve impulses in the sensory neuron.
2 Sensory neuron.
• The nerve impulses propagate along the axon of the sensory neuron to the axon
terminals, which are located in the gray matter of the spinal cord or brain stem.
3 Integrating center.
• One or more regions of gray matter within the CNS act as an integrating center.
• Monosynaptic reflex arc and polysynaptic reflex arc.

31. 4 Motor neuron.
• Impulses triggered by the integrating center propagate out of the CNS along a motor
neuron to the part of the body that will respond.
5 Effector.
• The part of the body that responds to the motor nerve impulse, such as a muscle or
gland, is the effector.
• Its action is called a reflex.
• If the effector is skeletal muscle, the reflex is a somatic reflex.
• If the effector is smooth muscle, cardiac muscle, or a gland, the reflex is an autonomic
(visceral) reflex.
• Damage or disease anywhere along its reflex arc can cause a reflex to be absent or
abnormal.

33. SPINAL NERVE

34. Spinal Nerve
•Spinal nerve are the path of communication between the
spinal cord and the specific region of the body
•31 pairs
•Spinal nerve follows the name of corresponding vertebra
column.
•Consists cervical spinal nerve, thoracic spinal nerve,
lumbar spinal nerve, sacral spinal nerve and coccyx spinal
nerve.
•Emerge from spinal cord and through the intervertebral
foramina of vertebra.

35. Spinal Nerve
1. 8 pairs of cervical spinal nerves
2. 12 pairs of thoracic spinal nerves
3. 5 pairs of lumbar spinal nerves.
4. 5 pairs of sacral spinal nerves
5. 1 pairs of coccyx spinal nerves.

36. • The spinal cord ends near the level of the superior border of the second
lumbar vertebra.
• The roots of the lumbar, sacral, and coccygeal nerves descend at an angle
to reach their respective foramina before emerging from the vertebral
column.
• This arrangement constitutes the cauda equina.
• Spinal nerve has two connections to the cord: a posterior root and an
anterior root.
• The posterior and anterior roots unite to form a spinal nerve at the
intervertebral foramen.
• Because the posterior root contains sensory axons and the anterior root
contains motor axons, a spinal nerve is classified as a mixed nerve.

37. Connective Tissue Coverings of Spinal Nerves
• Each spinal nerve consists of many individual axons and contains layers of
protective connective tissue coverings.
• Individual axons within a nerve are wrapped in endoneurium , the innermost
layer.
• Groups of axons with their endoneurium are arranged in bundles called
fascicles, each of which is wrapped in perineurium , the middle layer.
• The outermost covering over the entire nerve is the epineurium.

39. Distribution of Spinal Nerves
Branches:-
• A short distance after passing through its intervertebral foramen, a spinal nerve
divides into several branches.
• These branches are known as rami.
• The posterior (dorsal) ramus serves the deep muscles and skin of the posterior
surface of the trunk.
• The anterior (ventral) ramus serves the muscles and structures of the upper and
lower limbs and the skin of the lateral and anterior surfaces of the trunk.
• In addition, spinal nerves also give off a meningeal branch.
• This branch reenters the vertebral cavity through the intervertebral foramen and
supplies the vertebrae, vertebral ligaments, blood vessels of the spinal cord, and
meninges.
• Other branches of a spinal nerve are the rami communicantes, components of the
autonomic nervous system.

42. Plexuses:-
• In the cervical, lumbar and sacral regions the anterior rami unite near their origins to
form large masses of nerves, or plexuses.
• In this nerve fibres are regrouped and rearranged before proceeding to supply skin,
bones, muscles and joints of a particular area.
• These structures have a nerve supply from more than one spinal nerve and therefore
damage to one spinal nerve does not cause loss of function of a region.
• In the thoracic region the anterior rami do not form plexuses.
• The principal plexuses are the cervical plexus, brachial plexus, lumbar plexus, and
sacral plexus.
• A smaller coccygeal plexus is also present.
• Emerging from the plexuses are nerves bearing names.
• Each of the nerves in turn may have several branches named for the specific structures
they innervate.

44. DERMATOMES
• The skin over the entire body is supplied by somatic sensory neurons
• That carry nerve impulses from the skin into the spinal cord and brain.
• Each spinal nerve contains sensory neurons that serve a specific,
predictable segment of the body.
• The area of the skin that
• Provides sensory input to the CNS via one pair of spinal nerves
• Is called a dermatome.

45. Cervical plexus
• This is formed by the anterior rami of the first four cervical nerves.
• The superficial branches supply the structures at the back and side of the
head and the skin of the front of the neck to the level of the sternum.
• The deep branches supply muscles of the neck, e.g. the sternocleidomastoid
and the trapezius.
• The phrenic nerve originates from cervical roots 3,4 and 5 and passes
downwards through the thoracic cavity supply the muscle of the diaphragm
with impulses which stimulate contraction.

47. BRACHIAL PLEXUS
• The anterior rami of the lower four cervical nerves and a large part of the
first thoracic nerve form the brachial plexus.
• The branches of the brachial plexus supply the skin and muscles of the upper
limbs and some of the chest muscles.
• Five large nerves and a number of smaller ones emerge from this plexus,
each with a contribution from more than one nerve root, containing sensory,
motor and autonomic fibres:
• Axillary (circumflex) nerve: C5, 6
• Radial nerve: C5, 6, 7, 8, Tl
• Musculocutaneous nerve: C5, 6, 7
• Median nerve: C5, 6, 7, 8, Tl
• Ulnar nerve: C7, 8, Tl
• Medial cutaneous nerve: C8, Tl.

51. The axillary (circumflex) nerve:-
• Winds round the humerus at the level of the surgical neck.
• It then breaks up into minute branches to supply the deltoid muscle, shoulder joint
and overlying skin.
The radial nerve:-
• The largest branch of the brachial plexus.
• It supplies the triceps muscle behind the humerus, crosses in front of the elbow joint
then winds round to the back of the forearm to supply extensors of the wrist and
finger joints.
• It continues into the back of the hand to supply the skin of the thumb, the first two
fingers and the lateral half of the third finger.
The musculocutaneous nerve:-
• Passes downwards to the lateral aspect of the forearm.
• It supplies the muscles of the upper arm and the skin of the forearm.

52. The median nerve :-
• It passes in front of the elbow joint then down to supply the muscles of the front of
the forearm.
• It continues into the hand where it supplies small muscles and the skin of the front
of the thumb, the first two fingers and the lateral half of the third finger.
• It gives off no branches above the elbow.
The ulnar nerve:-
• It passes behind the humerus to supply the muscles of the forearm.
• It continues downwards to supply the muscles in the palm of the hand and the skin
of the whole of the little finger and the medial half of the third finger.
• It gives off no branches above the elbow.

53. Lumbar plexus
• Formed by the anterior rami of the first three and part of the fourth lumbar
nerves.
• The main branches, and their nerve roots are:
• Iliohypogastric nerve: L1
• Ilioinguinal nerve: L1
• Genitofemoral: L1, 2
• Lateral cutaneous nerve of thigh: L2, 3
• Femoral nerve: L2, 3,4
• Obturator nerve: L2, 3, 4
• Lumbosacral trunk: L4, (5).

56. Iliohypogastric, ilioinguinal and genitofemoral nerves:-
• Supply muscles and the skin in the area of the lower abdomen, upper and medial
aspects of the thigh.
Lateral cutaneous nerve of the thigh
• Supplies the skin of the lateral aspect of the thigh including part of the anterior and
posterior surfaces.
Femoral nerve
• The larger branches.
• It enter the thigh in close association with the femoral artery.
• It divides into cutaneous and muscular branches to supply the skin and the muscles of
the front of the thigh.
• One branch, the saphenous nerve, supplies the medial aspect of the leg, ankle and
foot.

59. Obturator nerve :-
• Supplies the adductor muscles of the thigh and skin of the medial aspect of the thigh.
• It ends just above the level of the knee joint.
Lumbosacral trunk:-
• Descends into the pelvis and makes a contribution to the sacral plexus.

60. SACRAL PLEXUS
• The sacral plexus is formed by the anterior rami of the lumbosacral trunk
and the first, second and third sacral nerves.
Lumbosacral trunk:-
• Formed by the fifth and part of the fourth lumbar nerves.
• It lies in the posterior wall of the pelvic cavity.
• The sacral plexus divides into a number of branches, supplying the muscles and skin of
the pelvic floor, muscles around the hip joint and the pelvic organs.
• In addition to these it provides the sciatic nerve which contains fibres from L4, 5, S1, 2,
3.
Sciatic nerve :-
• The largest nerve in the body.
• It is about 2 cm wide at its origin.
• It passes through the posterior aspect of the thigh supplying the hamstring muscles.
• At the level of the middle of the femur it divides to form the tibial and the common
peroneal nerves.

64. Tibial nerve:-
• Descends to the posterior aspect of the leg where it supplies muscles and skin.
• It supply muscles and skin of the sole of the foot and toes.
• One of the main branches is the sural nerve which supplies the tissues in the area of
the heel, the lateral aspect of the ankle and a part of the foot.
Common peroneal nerve:-
• Winds round the neck of the fibula into the front of the leg where it divides into the
deep peroneal (anterior tibial) and the superficial peroneal (musculocutaneous)
nerves.
• These nerves supply the skin and muscles of the anterior aspect of the leg and the
foot and toes.
Pudendal nerve (S2, 3, 4) :-
• Supplies the external anal sphincter, the external urethral sphincter and adjacent
skin.

65. Coccygeal plexus
• A very small plexus formed by part of the fourth and fifth sacral and the
coccygeal nerves.
• The nerves from this plexus supply the skin in the area of the coccyx and
muscles of the pelvic floor and the external anal sphincter.

66. Thoracic nerves
• The thoracic nerves do not intermingle to form plexuses.
• There are 12 pairs and the first 11 are the intercostal nerves.
• They pass between the ribs supplying them, the intercostal muscles and
overlying skin.
• The 12th pair are the subcostal nerves.
• The 7th to the 12th thoracic nerves also supply the muscles and the skin of
the posterior and anterior abdominal walls.