The vagus nerve: a true information highway


The vagus nerve is the longest nerve in the body, and one of the most important. It sends commands to, and takes information from, numerous important organs. People actually have two vagus nerves, one for each side, running a roughly parallel course from brain to bowels.

Originating in a part of the brain stem called the medulla oblongata, the vagus nerve passes through the face, down the throat, past the voice box, esophagus, lungs, heart, diaphragm and intestines. Along the way, this great river of nervous impulses throws off tributaries to these organs.

Vagus means "wandering" in medieval Latin, and now you know why. Other cognates of the word are "vagrant," "vague" and "vagabond."

Because it connects to so many organs, problems with the vagus can take many forms. If the left or right vagus nerve is completely cut near the top, the organs it controls are left partly functioning. The vocal cords on the affected side don't work; neither does the gag reflex on that side.

The multipurpose vagus nerve also controls sweating and heartbeat. It acts as an inhibitor. Stimulating the nerve causes the heart to slow down and also reduces activity of the diaphragm, the sheet of muscle below the stomach used in breathing. These are characteristic functions of the parasympathetic nervous system, to which the vagus belongs. It balances the activity of the sympathetic nervous system, which accelerates organ activities.

Overstimulation of the diaphragm plays a role in hiccups. As you might expect, stimulating the vagus nerve can calm the diaphragm, ending this exasperating condition. A few years back, a doctor reported success stopping hiccups with an unorthodox method of stimulating the vagus nerve -- a gloved finger inserted into the rectum. In 2006, Francis Fesmire of the University of Tennessee College of Medicine received the dubious honor called the Ig Nobel Prize for his medical paper: "Termination of intractable hiccups with digital rectal massage."

In a more dignified approach to the problem, a medical device called the vagus nerve stimulator has been used to control intractable hiccups. The device sends electrical impulses into the nerve. The vagus nerve stimulator has also been approved for the treatment of uncontrolled epileptic seizures. It's implanted in the chest near the collarbone, and turned on with a magnet when a seizure is starting. The device is also being tested for treating long-term intractable depression.

Other treatments involving the vagus nerve are in the testing stages. One, to control obesity, takes advantage of the nerve's connection to the stomach. The vagus nerve stimulates the stomach to produce its acidic digestive juice, and causes the brain to produce appetite-increasing hormones.

A study by researchers at UC San Francisco and the University of Rochester has found that of 11 patients who have had the vagus nerve connection to the stomach severed, 10 are losing weight one year after the operation.



