Twelve pairs of cranial nerves arise from the underside of the brain
Most are mixed nerves, containing sensory and motor nerve fibers, but some are only sensory, and others are primarily motor.
31 pair of spinal nerves arise from spinal cord and all except the first pair are mixed nerves
Numbered in sequence : 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves, and 1 pair of coccygeal nerves.
Each arises from from two roots : a sensory dorsal root, and a motor ventral root
Each dorsal root contains a dorsal root ganglion, which houses the cell bodies of sensory neurons entering the spinal cord.
A ventral root and dorsal root unite to form a spinal nerve, which extends out of the vertebral canal through the intervertebral foramen