Korva is a scroll of the internet’s best ideas.
Vagus means wandering
There are two of them, left and right. Theresa Larkin, an anatomist who has cut open cadavers, describes them as very prominent and glistening, a white yellow color. They touch tons of organs along the way.
When a big stress response has passed, these nerves can trigger a chill out response with its own tagline: rest, digest, restore. The vagus nerves help slow down the heart and the breathing, get the gut moving again, and reduce inflammation. They take the brain's instruction that it's time to chill out and spread the word to the rest of the body.
Why does the vagus nerve run so far?
Its path reflects the body's evolutionary history. In fish, the vagus served the gill region near the head, and as the heart and stomach shifted down the body in later animals, the nerve was stretched along with them. A branch called the recurrent laryngeal nerve loops under the aorta before climbing back up to the voice box. In giraffes that detour runs down the entire neck and back, a distance of several meters.
How do vagus nerves slow the heart?
They release a chemical called acetylcholine onto the heart's natural pacemaker, which slows its firing. Austrian pharmacologist Otto Loewi showed this in 1921 by stimulating the vagus nerve of one frog heart and moving the fluid around that heart to a second one, which also slowed. He called the substance Vagusstoff, or vagus material. The experiment is considered the first demonstration that nerves communicate with chemicals.
How does the vagus nerve reduce inflammation?
Kevin Tracey and colleagues reported in the journal Nature in 2000 that stimulating the vagus nerve in rats dampened the release of inflammatory molecules such as tumor necrosis factor. The circuit later became known as the inflammatory reflex, and it runs through the spleen. Immune cells there carry receptors that respond to the chemical signal released by the nerve's endings. The finding opened a field studying nerve stimulation for inflammatory disease.