The presence of a nervous system allows an animal to respond, in a coordinated manner, to both the demands of the external environment and the internal changes within its body.

The functions of the nervous system arc:

To receive stimuli from the external and internal environment

To analyse and integrate these stimuli

To bring about the necessary response.

Although the nervous system works as a well-inte­grated composite unit within the body, for descriptive purposes, it can be divided into:

1. Central nervous system (CNS) - the brain and spinal cord

2. Peripheral nervous system - all the nerves given off from the CNS.