Nervous System

The nervous system is a system of nerve cells, tissues, and organs which regulates the body's responses to internal and external stimuli through nervous impulses that travel fast through a complex network of cable-like nerves. In vertebrates it is composed of the brain, spinal cord, nerves, ganglia, and parts of the receptor and effector organs.

The nervous system is divided into three categories: the central nervous system; the peripheral nervous system; and autonomic nervous system. The central nervous system is made up of the brain, the cerebelum, and spinal cord, and is encased in the cranium and spinal column. The peripheral nervous system is composed of the long cable-like nerves that connect sensory nerve cells, to the spinal cord and brain. The autonomi nervous system is the part of the nervous system which regulates involuntary action, as of the liver, pancreas, intestines, heart, and glands.