Define the Peripheral Nervous System (PNS)
Peripheral nervous system consists of cranial and spinal nerves.
There are twelve pairs of cranial nerves. They arise from brain. Most of them arrive from brain stem. There are the thirty one pairs of spinal nerves arising from spinal cord. They have been named and numbered according to the vertebral region they belong to. Thus there are eight pairs of cervical spinal nerves from C1 to C8, twelve pairs of dorsal nerves from D1 to D12, five pairs of lumbar spinal nerves from L1 to L5, five pairs of sacral nerves from S1 to S5 and one pair of coccygeal nerve.