Overview of the Autonomic Nervous System

The autonomic nervous system (ANS) is made up of the sympathetic, parasympathetic, and enteric nervous systems. ¹

These three systems work together to maintain homeostasis, or your body’s ability to regulate normal function. ²

The ANS is responsible for all the body functions that we do automatically, without consciously thinking about performing. ³

The sympathetic nervous system usually stimulates organs (sometimes known as fight or flight.) ⁴

Sympathetic nervous system activation results in elevated blood pressure and heart rate, constriction of blood vessels, reduced digestion, dilation or opening of the airways, and more. ⁵

The parasympathetic nervous system maintains normal body functions (sometimes known as rest and digest.) ⁶

It can cause a decrease in heart rate and blood pressure, stimulate digestion, and more. ⁷ It is regulated mainly by the vagus nerve. ⁸

Sometimes, the sympathetic nervous system and parasympathetic nervous systems act as opposites, and sometimes they work together. ⁹

The enteric nervous system controls the muscle contractions, secretions, absorption, and blood flow during digestion. ¹⁰

Figure 1

(Figure 1 from Low, P. (2020, April). Overview of the autonomic nervous system. Merck Manual Consumer Version.)

Reviewed by Medical Content Experts, 2021

REFERENCES

Low, P. (2020, April). Overview of the autonomic nervous system. Merck Manual Consumer Version. {3, 4, 5, 6, 7, 9}

Waxenbaum, J.A., Reddy, V., & Varacallo, M. (2021). Anatomy, autonomic nervous system. In StatPearls. StatePearls Publishing. {1, 2, 8, 10}