ORGANIZATION OF THE NERVOUS SYSTEM

The nervous system is organised into two main divisions:

(a) the Central Nervous System (CNS) and (b) the periphereal nervous system (PNS)

(a) The Central Nervous System

The central nervous system comprises of the brain and the spinal cord

(b) The Peripheral Nervous System

The peripheral nervous system consists of nerve cells lying outside the CNS. It is further sub-divided into: (i) Autonomic nervous system, (ii)Somatic nervous system, and (iii) Enteric nervous system.

(i) Autonomic Nervous System (ANS)

("auto"=self; "nomos" governing)

In ANS the receptors are located in internal organs and hence it is involuntary in nature.

Further, it comprises of two subdivisions:

* Sympathetic nervous system and 

*Parasympathetic nervous system. Nerve fibre endings of sympathetic nervous system release Epinephrine/Nor-epinephrine as a neurotransmitter and that of parasympathetic nervous system release Acetylcholine. The two systems act  opposite to each other, e.g., sympathetic nerve fibres increase the heart rate whereas  parasympathetic system decreases it.

 (ii) Somatic Nervous System (SNS)

In the SNS receptors are found in skin, limbs and upper part of the body It also includes special sense organs viz. eye, ear, nose, etc.

(iii) Enteric Nervous System (ENS)

Once considered part of the ANC, it is also known as the brain of the gut". It consists of approximately 100 million neurons  and its operation is involuntary

STRUCTURE OF BRAIN SPINAL CORD AND THEIR FUNCTION