What is the vagus nerve?

Structure and Function

The vagus nerve is actually two nerves that run from the brain stem and exit from the skull at its base through the jugular foramen and descend the neck through the carotid sheath between the internal carotid artery and the internal jugular vein. The vagus nerve passes not only through the neck and head but also through the chest and abdomen, where it contributes to the innervation of the viscera. The superior laryngeal nerve is the first branch that travels with the superior thyroid artery, whereby this nerve innervates the cricothyroid muscle through its external branch, thus supplying sensation to the supraglottic larynx. The facial nerve, the glossopharyngeal nerve, and the vagus nerve can all recognize flavor. The swallowing reflex is connected to the vagus nerve as well.

Activation of the vagus nerve lowers blood pressure and reduces the heart rate, which typically occurs with gastrointestinal illness (acute cholecystitis or viral gastroenteritis) or in response to other stimuli such as the Valsalva maneuver or pain in having blood drawn.

Disorders and Diseases

The vagus nerve can be tested by a clinician through the gag reflex, usually with a tongue depressor or observing the uvula and the back of the throat when the patient speaks. If anything about these processes is unusual, then further examination of the ninth and tenth cranial nerves is warranted. Some people who suffer from a congenital vagus nerve disorder may have trouble breathing and may need a breathing apparatus or even a pacemaker to keep the heart regular. Fainting can possibly be related to a vagus nerve problem.

A particular disorder related to the vagus nerve is called gastroparesis or delayed gastric emptying, in which the stomach takes a longer time than usual to empty food into the small intestines for the digestion process. This disease occurs when the vagus nerve is damaged and the muscles of the intestines and stomach do not function correctly. The food slows down or completely stops in the digestive tract. The most common cause of gastroparesis is diabetes. When the blood sugar is high, a chemical reaction occurs in the nerves that damages blood vessels that carry nutrients and much-needed oxygen.

Perspective and Prospects

Vagotomy is the cutting of the vagus nerve to reduce acid buildup to the stomach. Vagotomy is being researched as a less invasive procedure for weight loss than gastric bypass surgery. Another procedure, vagus nerve stimulation (VNS), is sometimes used to treat conditions such as epilepsy and drug-resistant depression. Wider applications for VNS are under study.

Bibliography

"Cranial Nerve X—Vagus." Yale University School of Medicine, January 8, 1998.

Flint, Paul W., et al., eds. Cummings Otolaryngology: Head and Neck Surgery. 5th ed. Philadelphia: Mosby/Elsevier, 2010.

“Motor Speech and Swallowing Disorders.” In Neurology and Clinical Neuroscience, edited by Anthony H. V. Schapira et al. Philadelphia: Mosby Elsevier, 2007.

“Sarcoidosis of the Nervous System.” In Neurology and General Medicine, edited by Michael J. Aminoff. 4th ed. Philadelphia: Churchill Livingstone, 2008.

"VNS." Epilepsy Foundation, 2012.