Autonomic Nervous System
The autonomic nervous system (ANS) is the part of the body’s peripheral nervous system responsible for maintaining homeostasis, or balance. As opposed to the sensory nervous system, which regulates part of the body which we can control voluntarily (e.g. muscles), the ANS regulates functions which are mainly involuntary. Involuntary functions include heart rate, digestion, dilation and constriction of blood vessels, and hormone secretion, among others.
The ANS is primarily composed of two branches: the Parasympathetic Nervous System and the Sympathetic Nervous System. The Sympathetic and Parasympathetic branches constantly work in opposition to one another to achieve and maintain a balanced physiological state.