# Autonomic nervous system

The autonomic nervous system (ANS) runs all the things you do not consciously control: heart rate, blood pressure, digestion, breathing. It has two main branches. The sympathetic branch is your 'fight-or-flight' accelerator. The parasympathetic branch is your 'rest-and-digest' brake. A semi-independent third branch, the enteric nervous system, runs your gut. In longevity science, doctors gauge how well your ANS is working through HRV (heart-rate variability), baroreflex sensitivity, and how fast your heart rate recovers after exercise. That is because a poorly balanced ANS, stuck in chronic 'fight-or-flight' mode (dysautonomia), is tied to heart disease and faster biological aging.

## Sources

- Malik M, Bigger JT, Camm AJ, et al.. (1996). Heart rate variability: Standards of measurement, physiological interpretation, and clinical use. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. European Heart Journal. https://doi.org/10.1093/oxfordjournals.eurheartj.a014868
- Errico JP, Ben-Azu B, Gargus M, et al.. (2025). Sympathetic-parasympathetic system deregulation theory of aging. npj Aging. https://doi.org/10.1038/s41514-025-00293-2

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_Canonical: https://longevity-switzerland.com/en/glossary/autonomic-nervous-system · Part of Longevity Cities · Updated 2026-06-22_