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Nerve: Spinal nerve
Spinal nerve.svg
The formation of the spinal nerve from the dorsal and ventral roots
Latin nervi spinales
Gray's subject #208 916
MeSH Spinal+nerves

The term spinal nerve generally refers to the mixed spinal nerve, which is formed from the dorsal and ventral roots that come out of the spinal cord. The spinal nerve is the bit that passes out of the vertebrae through the intervertebral foramen. All spinal nerves are part of the peripheral nervous system (PNS). There are 31 pairs of spinal nerves in humans.

Formation of the spinal nerves

Inside the spinal cord, there is grey matter, surrounded by white matter. From out of the grey matter, two dorsal roots (one on the left side, and one on the right side) and two ventral roots emerge. (Dorsal means back, ventral means front.)The same thing happens on both the left and right side of the body. This happens between each vertebra of the spine.

  • The ventral roots contain efferent motor axons. Similar to the dorsal roots, the ventral roots continue out from the spinal column, and meet and mix with their corresponding dorsal nerve root at a point after the ganglion.

At this point, the combination of the dorsal roots and ventral roots is called a mixed spinal nerve.

Importance of the spinal nerves

The muscles that one particular spinal root supplies are that nerve's myotome, and the dermatomes are the areas of sensory innervation on the skin for each spinal nerve.

This is of great importance in the diagnosis of neurological disorders, as lesions of one or more nerve roots result in typical patterns of neurologic defects (muscle weakness, loss of sensation) that allow localisation of the causeating lesion.

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