The autonomic nervous system (ANS), also called the visceral nervous system, is a control system that operates largely unconsciously and regulates internal organs, smooth muscle, and glands. The ANS is integral to maintaining vital functions and adapting to stress and recovery cycles. It controls bodily functions such as heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal. The ANS is regulated by integrated reflexes through the brainstem to the spinal cord and organs and is influenced by the hypothalamus, which receives regulatory input from the limbic system.
The ANS has two main divisions: the sympathetic nervous system and the parasympathetic nervous system. The sympathetic system triggers the "fight-or-flight" response, preparing the body for strenuous activity by increasing heart rate, widening airways, and releasing energy. The parasympathetic system controls "rest and digest" functions, conserving energy and regulating basic functions like digestion and urination. Recent research has revealed that the ANS can spontaneously restore muscle function after a nerve injury, with parasympathetic nerve fibers forming new connections to take over the function of the injured nerve. A 2024 study highlighted the diversity within the sympathetic nervous system, uncovering specific neuron populations that control visceral functions in an organ-specific manner, offering new insights into how the brain modulates body functions.
