Dictionary of Biological Psychology
Spinal nerves are formed by the axons of dorsal (posterior) and ventral (anterior) roots that arise throughout the length of the spinal cord. DORSAL ROOTS contain sensory axons and aggregations of cell bodies (DORSAL ROOT GANGLIA) of sensory neurons.
Ventral roots contain axons of somatomotor neurons and, at thoracic and sacral levels, they also contain autonomic preganglionic axons. The roots unite to form segmentally arranged, mixed spinal nerves. In humans, there are 31 pairs grouped and numbered according to the corresponding vertebrae, thus forming 8 cervical, 12 thoracic, 5 lumbar, 5 sacral pairs and 1 coccygeal pair of spinal nerves.
See also: cranial nerves; peripheral nervous system; spinal cord
DAVID A.HOPKINS
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