Autonomic nervous system is the part of the Peripheral Nervous System (PNS), which control the unconscious functions of body. Autonomic nervous system controls involuntary activities of the body, like sweating, salivation, peristalsis, etc. It differs fundamentally from the somatic nervous system in having:
- The preganglionic fibers arising from the CNS
- The ganglia for relay of the preganglionic fibers
- The postganglionic fibers arising from the ganglia which supply the effectors (smooth muscles and glands).
In contrast, the somatic nerves after arising from the CNS reach their destination without any interruption.
Autonomic nervous system is divided into two more or less complementary parts: the sympathetic nervous system and parasympathetic nervous system.
The sympathetic activities are widespread and diffuse, and combat the acute emergencies. The parasympathetic activities are usually discrete and isolated, and provide a comfortable environment. Both systems function in absolute coordination and adjust the body involuntarily to the given surroundings.