This system regulates the functioning of internal organs (called viscera) such as the heart, stomach, and intestines. The ANS is part of the peripheral nervous system and also controls some muscles within the body.
While it usually functions involuntarily, controlling things such as vasoconstriction and vasodilation, some people can learn how to control certain functions such as heart rate and digestion using biofeedback. This makes us aware of things that would normally pass our attention and sees how our breathing, thinking and bodily movements affect them.
The ANS is divided into 3 main systems:
- The enteric nervous system
- The sympathetic nervous system
- The parasympathetic nervous system
The enteric nervous system (ENS) refers to a system of neurons found in the gastrointestinal system. The ENS is sometimes referred to as a 'second brain' due to the capability of its neurons to form 'memories', 'thoughts' and undertake learning.
The ANS is important both in the "fight or flight" response (primarily controlled by the sympathetic nervous system) and also the "rest and digest" response (primarily controlled by the parasympathetic nervous system).
When the sympathetic nervous system is stimulated, usually, energy is used up more quickly; blood pressure increases, the heart beats faster, digestion slows and the immune system is suppressed.
When the parasympathetic nervous system is stimulated, usually, energy is used up less quickly; blood pressure decreases, the heart beats slower, digestion speeds up and the immune system remains active.
The sympathetic and parasympathetic nervous systems operate independently in some functions and co-operatively in others. While they usually have opposing actions (where one initiates a response and the other inhibits it), there are cases in which they both work together. Examples of this are sexual arousal and orgasm.