Nerve root

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A nerve root (Latin: radix nervi) is the initial segment of a nerve leaving the central nervous system. Nerve roots can be classified as:

• Cranial nerve roots: the initial or proximal segment of one of the twelve pairs of cranial nerves leaving the central nervous system from the brain stem or the highest levels of the spinal cord.
• Spinal nerve roots: the initial or proximal segment of one of the 31 pairs of spinal nerves leaving the central nervous system from the spinal cord. Each spinal nerve is a mixed nerve formed by the union of a sensory dorsal root and a motor ventral root,^[1] meaning that there are 62 dorsal/ventral root pairs, and therefore 124 nerve roots in total, each of which stems from a bundle of nerve rootlets (or root filaments).