Merck Manual

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Sympathetic Innervation
Sympathetic Innervation

The sympathetic division is part of the autonomic nervous system—the part of the nervous system that works automatically (autonomously), without a person's conscious effort, to regulate internal body processes.

Generally, the sympathetic division prepares the body for stressful or emergency situations—fight or flight. For example, it increases heart rate and the force of heart contractions and widens (dilates) the airways to make breathing easier.