Vagus nerve



The vagus nerve, also called the tenth cranial nerve, starts in the brain and runs down the trunk of the body, with branches innervating the major organs. It interfaces with the parasympathetic nervous system and helps to regulate the heart, lungs, and the digestive system. It's a bi-directional nerve, meaning it both sends signals from the brain to the organs and the organs send messages back to the brain.

Immune system
The vagus nerve speaks directly to the immune system via the neurotransmitter acetylcholine.

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 * Sympathetic nervous system