The autonomic nervous system is the part of the nervous system of the higher life forms that is not consciously controlled. It is commonly divided into two usually antagonistic subsystems: the sympathetic and parasympathetic nervous system.

The autonomic nervous system (ANS) (or visceral nervous system) is the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These maintenance activities are primarily performed without conscious control or sensation. The ANS has far-reaching effects, including heart rate, digestion, respiration rate, salivation, perspiration, the diameter of the pupils, micturition (the discharge of urine), and sexual arousal. Whereas most of its actions are involuntary, some ANS functions work in tandem with the conscious mind, such as breathing. Its main components are its sensory system, motor system (comprised of the parasympathetic nervous system and sympathetic nervous system), and the enteric nervous system.