Spinal Cord

Spinal Cord (neuraxis):
Rope like bundle of afferent and efferent neurons. Main function is to connect the brain with the peripheral and autonomic systems (two-way conduction pathway), as well as being responsible for reflexes and the central pattern generator (co-ordination of locomotion). Proximally it is a continuation of medulla oblongata; distally it tapers to cone shaped structure (conus medullaris) – fibrous extension of pia mater (filum terminales) attached to posterior aspect of coccyx  anchors spinal cord. The cauda equina is the collection of nerve roots at distal end. Spinal cord is enclosed in vertebral column – average 42cm in length and 1.8cm in diameter. Spinal canal is 5 to 9 cm longer in flexion and extension  plasticity and mobility of neural tissue is significant. Denticulate ligaments attach spinal cord along its length to vertebrae. 31 pairs of spinal nerves arise from spinal cord exit via intervertebral foramina. The spinal cord is protected by bone, CSF and meninges.

Gray matter of spinal cord:
Inner core of spinal cord. Looks like ‘H’ or ‘butterfly’ in cross section – with two posterior projections (posterior/dorsal horns) and two anterior projections (anterior/ventral horns) – connected by gray commissure. Anterior or ventral horns – mainly contain nerve cell bodies of somatic motor neurons  axons exit thru ventral roots of spinal cord. Posterior or dorsal horns – contain interneurons.

White matter of spinal cord:
Composed of myelinated and unmyelinated nerve fibres running longitudinally.

Cauda equina – bundle of nerves that descends in the spinal column before exiting

Subdivisions of spinal cord:
7 cervical vertebrae (‘top’)
12 thoracic vertebrae
5 lumbar vertebrae
3 sacral vertebrae
1 to 3 coccygeal vertebrae

Enlargements in the lower cervical (brachial plexus) and lumbosacral (lumbosacral plexus) areas formed by large number of nerve cells that collect in these areas  innervate upper and lower extremities.

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