The autonomic nervous system is part of the nervous system that regulates involuntary action, such as the heartbeat and perspiration. Its key function is to transmit nerve signals from the central nervous system to the peripheral organ systems, including the cardiovascular system and gastrointestinal system.

The autonomic nervous system is divided into two systems: the sympathetic nervous system and the parasympathetic nervous system, which typically work in opposition to each other. For example, the sympathetic nervous system regulates increases in heart rate during exertion or fright, while the parasympathetic nervous system regulates decreases in heart rate during rest.