The spinal cord begins at the foramen magnum and extends down to the L1-L2 vertebrae. It has 31 segments and is enlarged in the cervical and lumbar regions. It is protected by vertebrae, meninges, and cerebrospinal fluid. The spinal cord contains gray matter with dorsal and ventral horns and white matter tracts. It transmits motor and sensory signals between the brain and body.

1. Dr. Bikal Lamichhane
1st year resident NAMS
Internal Medicine
Anatomy Of Spinal Cord

2.  The spinal cord is the major reflex center and conduction pathway between the body and
brain.
 This cylindrical structure,slightly flattened anteriorly and posteriorly, is protected by the
vertebrae, their associated ligaments and muscles, the spinal meninges, and the
cerebrospinal fluid (CSF).
 The spinal cord begins as a continuation of the medulla oblongata, the caudal part of the
brainstem.
 In adults, the spinal cord is 42–45 cm long and extends from the foramen magnum in the
occipital bone to the level of the L1 or L2 vertebra .
 However, its tapering inferior end, the conus medullaris, may terminate as high as T12
vertebra or as low as L3 vertebra.
 Thus the spinal cord occupies only the superior two thirds of the vertebral canal.

3. Contd….
 There are 31 spinal cord segments, each with a pair of ventral (anterior) and
dorsal (posterior) spinal nerve roots, which mediate motor and sensory function,
respectively.
 It has two enlargements,
 Cervical enlargements: supply upper limbs
 Lumbosacral enlargements:supplies lower limbs
 The ventral and dorsal nerve roots combine on each side to form the spinal
nerves as they exit from the vertebral column through the neuroforamina.

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6. Spinal Meninges
1. Spinal dura matter
 a prolongation of the inner layer of the dura mater of the posterior cranial fossa. •
 It extends downwards through the foramen magnum to the level of S2 vertebra.
 • It is attached rather firmly to the tectorial membrane ( and to the posterior longitudinal
ligament on the body of the axis vertebra.
2. Spinal arachnoid matter
 The spinal arachnoid mater is supported by the inner surface of the spinal dura; nothing
but a thin film of lymph separates these two membranes.
 Below the level of the spinal cord (i.e. over the cauda equina) the arachnoid is nothing
but a delicate membrane that is supported by the dura mater.
3. Spinal pia mater
• It clothes the spinal cord and enters to line the anterior median sulcus.
 It is prolonged over the spinal nerve roots and blends with their epineurium.

7.  The spinal cord is enlarged in two regions in relationship to innervation of the
limbs.
 The cervical enlargement extendsfrom C4 through T1 segments of the spinal
cord, and most of the anterior rami of the spinal nerves arising from it form the
brachial plexus of nerves that innervates the upper limbs.
 The lumbosacral (lumbar) enlargement extends from T11 through S1 segments
of the spinal cord, inferior to which the cord continues to diminish as the conus
medullaris.
 The anterior rami of the spinal nerves arising from this enlargement make up the
lumbar and sacral plexuses of nerves that innervate the lower limbs.

8. Spinal cord segment
 The portion of the spinal cord giving rise to the rootlets and roots that ultimately
form one bilateral pair of spinal nerves is designated a spinal cord segment, the
identity of which is the same as the spinal nerves arising from it.
 There are 31 spinal cord segments, each with a pair of ventral (anterior) and
dorsal (posterior) spinal nerve roots, which mediate motor and sensory function,
respectively. The ventral and dorsal nerve roots combine on each side to form the
spinal nerves as they exit from the vertebral column through the neuroforamina

9. Longitudinal organization
 The spinal cord is divided longitudinally into four regions: the cervical,
thoracic, lumbar, and sacral cord.
 The spinal cord extends from the base of the skull and terminates near the
lower margin of the first lumbar vertebral body (L1).
 Below that level, the spinal canal contains the lumbar, sacral, and coccygeal
spinal nerve roots that comprise the cauda equina.

11. Cervical cord
 The first cervical vertebra (the atlas) and the second cervical vertebra (the axis), upon
which the atlas pivots, support the head at the atlanto-occiput junction. The interface
between the first and second vertebra is called the atlanto-axis junction.
 Cervical spinal segments innervate the skin and musculature of the upper extremity and
diaphragm.
 C3 through C5 innervate the diaphragm, the chief muscle of inspiration, via the phrenic
nerve
 C4 through C7 innervate the shoulder and arm musculature
 C6 through C8 innervate the forearm extensors and flexors
 C8 through T1 innervate the hand musculature

13. Thoracic cord
 The thoracic vertebral segments are defined by those that have an attached
rib.
 The spinal roots form the intercostal nerves that run along the inferior rib
margin and innervate the associated dermatomes, as well as the intercostal
abdominal wall musculature.
 The thoracic cord also contains the sympathetic nerves that innervate the
heart and abdominal organs

14. Lumbosacral cord
 The lumbosacral spinal cord contains the segments that
innervate the muscles and dermatomes of the lower
extremity, as well as the buttocks and anal regions .
 Sacral nerve roots S3 through S5 originate in the narrow
terminal part of the cord, called the conus medullaris.
 Sacral nerve roots also provide parasympathetic
innervation of pelvic and abdominal organs, while
lumbar nerve roots L1 and L2 contain sympathetic
innervation of some pelvic and abdominal organs.

15. Cauda equina
 In adults, the spinal cord ends at the level of the first or second lumbar
vertebral bodies.
 The filum terminale, a thin connective tissue filament that descends from
the conus medullaris with the spinal nerve roots, is connected to the third,
fourth, and fifth sacral vertebrae; its terminal part is fused to the periosteum
at the base of the coccygeal bone.
 Pathology at the T12 and L1 vertebral level affects the lumbar cord. Injuries
to L2 frequently damage the conus medullaris. Injuries below L2 usually
involve the cauda equina and represent injuries to spinal roots rather than to
the spinal cord

16. Cross-sectional anatomy
 The spinal cord contains the gray matter, the butterfly-shaped central
region, and the surrounding white matter tracts.
 The spinal cord gray matter, which contains the neuronal cell bodies, is
made up of the dorsal and ventral horns, each divided into several laminae

17. GRAY MATTER
 Dorsal horn
 The dorsal horn is the entry point of sensory information into the central nervous system.
 It is divided into six layers or laminae that process sensory information.
 More than a relay station for the transmission of sensory information, the dorsal horn also
modulates pain transmission through spinal and supraspinal regulatory circuits.
 Ventral horn
 The motor nuclei of the spinal cord are contained within the ventral horn, which also
contains interneurons mediating information from other descending tracts of the
pyramidal and extrapyramidal motor systems.
 These ultimately synapse on the alpha and gamma motor neurons, which subsequently
leave the ventral horn via the ventral nerve root to terminate at the neuromuscular
junction.

18. White matter
 A collection of nerve fibers that connects two grey matter with CNS is
called white matter tract.
 Tracts may be ascending or descending.
 They are named after the masses of grey matter connected by them.