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nerve root
In vertebrates, each spinal nerve arises from the spinal cord by two roots: a dorsal (posterior in human anatomy) and a ventral (anterior in human anatomy) which join to form the spinal nerve as they pass through the wall of the vertebral column. The dorsal roots contain all the sensory nerve fibers, their cell bodies being in a ganglion on the course of each root; in some vertebrates they may also contain a few motor fibers. Through the ventral roots pass the motor fibers, their cell bodies being in the spinal cord.
Cranial nerves can also be classified into dorsal and ventral roots, which however do not join, remaining separate nerves. Cranial dorsal roots have ganglia and contain, besides sensory, numerous motor fibers running to the face, jaw, and (in fish) gill muscles, and motor fibers of the parasympathetic system. Cranial ventral roots contain some sensory (proprioceptor) fibers.
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