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. In man, there are 12 pairs of cranial nerves. Some of the cranial nerves are sensory.
Nerves arising from the spinal cord are called spinal nerves. In man, there are 31 pairs of spinal nerves. Each spinal nerve has a dorsal sensory root and the ventral motor root.