. Human nervous system is divisible into three main parts :
(a) Central Nervous System : It is a hollow, dorsally placed structure lying along the mid-dorsal axis of the body. It comprises the brain and spinal cord.
(b) Peripheral Nervous System : The nerves arising from the central nervous system constitute the peripheral nervous system. The nerves originate from the brain and spinal cord and are known as cranial nerves and spinal nerves respectively.
(b) Autonomic Nervous System : It controls and co-ordinates such organs which are under involuntary control. It consists of sympathetic and parasympathetic nervous system.