Autonomic Nervous System

The autonomic nervous system (ANS) maintains homeostatic processes in the body and enables flexible responding to stress under conditions of challenge. It is made up of the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS), each of which exerts its effects over the body by secreting different chemicals that regulate behavior in response to sensory input. The SNS is charged with mounting a fight-or-flight response, and the PNS is responsible for maintaining homeostasis or promoting return to homeostasis after the experience of a threat or stressor. The flexibility of the ANS supports effective social engagement and relationship formation across the lifespan. This entry defines and describes the ANS, describes the most common noninvasive measurement techniques, and discusses implications for lifespan human development.