Nervous system
ANS
Definition
The autonomic nervous system is the part of the nervous system that helps regulate internal functions such as circulation, digestion, temperature, and adaptation to changing demands.
Aliases and abbreviations
ANS · autonomic regulation system
Editorial record
Published: August 25, 2026 · Reviewed: August 25, 2026
Expanded definition
The ANS is commonly described through sympathetic and parasympathetic divisions. These systems interact continuously rather than operating as two simple buttons that alternate between “on” and “off”.
Autonomic activity changes with posture, breathing, movement, sleep, emotion, illness, medication, environment, and many other influences. Flexible regulation matters more than trying to maximise one branch at all times.
Measures such as heart rate and HRV can provide partial information about autonomic patterns, but no single number captures the whole system.
What the term does not establish
Why the distinction matters
The term provides the wider physiological context for stress responses, parasympathetic activity, HRV, vagal tone, and VNS research.
Main guide
A research overview of sympathetic, parasympathetic, and flexible brain–body regulation.
Explore autonomic regulationRelated terms
Nervous system
Nervous system
Anatomy
Measurement and interpretation
Measurement and interpretation
Editorial scope
This glossary entry supports general education. It does not diagnose, recommend treatment, or transfer findings from one VNS method, protocol, or device to another.