Peripheral Nervous System
Peripheral nervous system is formed by the nerves arising from the brain and the spinal cord. The nerves arising from the brain are called cranial nerves. Nerves arising from spinal cord are called spinal nerves.
In man, there are 12 pairs of cranial nerves. Some of the cranial nerves are sensory e.g. optic nerve which innervates the eye. Some are motor nerves which helps in rotation of eyeball. It also innervates the eye muscles, muscles of iris and tear gland.
There are 31 pairs of spinal nerves. Each spinal nerve has a dorsal sensory root and the ventral motor root. The direction of impulses in dorsal spinal root is towards the spinal cord and in ventral spinal root away from the spinal cord.