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Spinal cord

  • The spinal cord is an elongated cylidrical lower part of CNS occupying upper two thirds of vertebral canal. It is enveloped by three meningeal layers - dura, arachnoid and pia maters. Spinal cord gives origin to 31 pairs of spinal nerves, (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal). The spinal cord begins as a continuation of medulla oblongata at the level of upper border of atlas (C 1 vertebra) and ends at lower border of L1 in adults. In newborn its termination is at L3 level. Spinal cord is as long as vertebral canal till 3rd month intrauterine life and therefore vertebral column grows more rapidly so that at birth the level of termination lies at L3 level. Inferiorly spinal cord terminates as conus medullaris. It is 18 inches (45 cm) long in adult male and 42 cm long in adult female. It is not uniformly cylindrical but two enlargements: cervical (C3 - T 2) and lumbar. (LI-S3)


Spinal meninges

  • Spinal meninges are continuous above with cerebral meninges. Outermost is dura mater, middle one is arachnoid mater, and innermost is pia mater. The space between dura and arachnoid maters is called subdural space. The space between arachnoid and pia maters is called subarachnoid space. Space outside the dura is called extradural (epidural) space.
  • The spinal cord extends in the lower part of L1 as conus medullaris. Below the level of conus medullaris only pia mater is continued as a thin fibrous cord, the filum terminate extending to first segment of coccyx. Below lower border of L1, this collection of nerve roots is called as cauda equina. Cauda equina is formed by lower four pairs of lumbar, five pairs of sacral and one pair of coccygeal spinal nerves. Both arachnoid mater and subarachnoid space end at S2 levels. Subdural space also ends at S2 level.

Tracts in spinal cord

  1. Ascending tracts       





Crossing over

Sensations carried

1. Anterior spinothalamic tract

Joins with medial lemniscus in pons and ends in the ventroposterolateral nucleus of the thalamus

Ascends 2 to 3 spinal segments and then Crosses to the opposite side

- Non-discriminative touch

- Pressure

2. Lateral spinothalamic tract

Forms the spinal lemniscus in the pons and ends in the ventro-posterolateral (VPL) nucleus and intra laminar nuclei of thalamus

Crosses to opposite side in the same spinal segment

- Pain

- Temperature

3. Anterior/ventral spinocerebellar tract

Ipsilateral anterior cerebellar vermis via superior Cerebeller peduncle.

a)  First it crosses to opposite side in the same spinal segment

b)  Crosses back to same side at the level of midbrain through the superior cerebellar peduncle

- Unconscious pro- prioception and exteroceptive information from the lower part of the body and lower limbs

- Responsible for maintaining posture and gross movement of entire lower limb

4. Posterior/dorsal spinocerebellar tract

The fibers pass via the ipsilateral inferior cerebellar peduncle to the


The fibers ascend ipsilaterally. They do not cross to opposite side

- Unconscious pro- prioception and touch and pressure from lower half of the body and lower extremity

- Responsible for the fine coordination between movements of various muscles of lower limb

5. Dorsal column a) Fasciculus gracilis b)Fasciculus cuneatus

Nucleus gracilis in lower medulla

Nucleus cuneatus in lower medulla

Fibers arising from nucleus gracilis and cuneatus decussate in the medulla to form the medial lemniscus

Conscious kinetic and static proprioception, vibration sense, discriminatory touch, and pressure from lower limb and lower half the body is carried by fasciculus gracilis and from upper limb and upper half of the body by fasciculus


  1. Descending Tracts



Crossing over


I. Corticospial or

pyramidal tract

passes through the

pyramid of medulla

Area 4,6 of

cerebral cortex


a) Lateral corticospinal

tract decussates in

lower part of medulla

b) Anterior corticospinal
tract crosses to opposite
side in the corresponding

spinal segment

- Responsible for skillful voluntary movements

- Facilitates flexors and is inhibitory to extensors

2. Rubrospinal tract


Red nucleus of


Midbrain at the level of superior colliculus

Same as corticospinal tract

3. Tectospinal tract

Superior coliculus

(Tectum of midbrain)

Midbrain at the level of superior colliculus

Reflex pathway for turning head and moving arm in response to visual and hearing stimuli

4. Olivospinal tract

Inferior olivary nucleus




Blood supply




Branch of

Territory of supply

1.Anterior spinal artery

(1 in number)

4th part of vertebral artery


Ventral 2/3rd cross section of spinal cord

2.Posterior spinal arteries

(2 in number)

4th part of vertebral artery, sometimes from posterior inferior cerebellar artery

Posterior lI3rd of the cross-section of spinal cord

3. Segmental spinal branches


(a) Vertebral artery (2nd part)

(b) Deep cervical artery

1. Anterior spinal artery

(1 in number)


1.Posterior spinal arteries

(2 in number)


3.Segmental spinal branches


(a) Vertebral artery (2nd part)


(c) Ascending cervical artery

(d) Posterior intercostal arteries

(e) Lumbar arteries

- Subclavian artery

- Costocervical trunk of 2nd


part of subclavian

- Branch of thyrocervical trunk

- Thoracic aorta

- Abdominal aorta


- ( a), (b) and (c) supply the cervical segments and uppermost thoracic

segments up to T2

- (d) and ( e) supply rest of the cord

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