Corpus: Autonomic nervous system

The autonomic nervous system, for short ANS, is the part of the nervous system that functions largely outside of voluntary control, meaning it operates "autonomously."

Physiologically, the nervous system is divided into the autonomic and somatic nervous systems.

The distinction between the autonomic and somatic nervous systems is not always clear-cut. For example, some functions of the somatic nervous system, like motor reflexes, are not under voluntary control by the brain. In older anatomical literature, the autonomic nervous system was considered part of the peripheral nervous system. This perspective is now outdated because many autonomic control centers, such as the respiratory center, are located in the brain.

The autonomic nervous system regulates essential life functions, such as breathing, digestion, and metabolism. It also influences specific organs or systems, such as the reproductive organs and the muscles of the inner eye.

The autonomic nervous system is divided into three components:

• The sympathetic nervous system
• The parasympathetic nervous system
• The enteric nervous system

Some authors consider the enteric nervous system to be an independent system in its own right.

The sympathetic and parasympathetic systems have opposing effects on their target organs. Broadly speaking, the sympathetic nervous system is responsible for rapid responses to environmental stimuli and mobilization of the body ("fight or flight"), while the parasympathetic nervous system facilitates relaxation and inward-directed activities ("rest and digest"). However, the idea of "opposition" is not absolute. Many bodily functions, such as sexual activity, require the simultaneous and coordinated action of both systems.

Like the somatic nervous system, the autonomic nervous system can both receive sensory information and send motor commands. Accordingly, autonomic nerves are categorized as:

• Viscerosensory fibers
• Visceromotor fibers