Vagus nerve anatomy

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The vagus nerve is the longest nerve in the autonomic nervous system and one of the most important nerves in the body. The vagus nerve helps regulate many important aspects of human physiology, including heart rate, blood pressure, sweating, digestion, and even speech. For this reason, medical science has long sought ways to regulate vagus nerve function.

Vagus nerve anatomy

The vagus nerve (also known as the 10th cranial nerve or cranial nerve X) is a very long nerve that originates in the brainstem and runs down the neck to the chest and abdomen. It carries motor and sensory information and also supplies innervation to the heart, major blood vessels, respiratory tract, lungs, esophagus, stomach, and intestines .

Although there are actually two vagus nerves (left and right), clinicians commonly refer to them collectively as the "vagus nerve."

The vagus nerve helps control various muscles in the throat and vocal apparatus. It plays an important role in the regulation of heart rate and the maintenance of the gastrointestinal tract. The vagus nerves also carry sensory information from internal organs to the brain.

Terry Vine / Getty Images

Vagus nerve function

Perhaps the most important of the vagus nerve is that it is the main parasympathetic nerve in the body, supplying parasympathetic fibers to all the major organs of the head, neck, chest, and abdomen. The vagus nerve is responsible for the gag reflex (and the cough reflex when the ear canal is stimulated), slowing the heart rate, controlling sweating, regulating blood pressure , stimulating peristalsis of the gastrointestinal tract, and controlling vascular tone. .

Vasovagal reflex

Sudden stimulation of the vagus nerve can trigger the so-called " vasovagal reflex ", which involves a sharp drop in blood pressure and a decrease in heart rate. This reflex can be caused by a gastrointestinal disease or in response to pain, fear. or sudden stress. Some people are particularly prone to the vasovagal reflex, and changes in blood pressure and heart rate can cause fainting, a condition called " vasovagal syncope . "

Excessive activation of the vagus nerve is also seen in certain diseases, especially dysautonomia .

Stimulating the vagus nerve can have therapeutic effects (such as stopping episodes of supraventricular tachycardia (SVT) or hiccups ) and can help doctors diagnose certain types of murmurs. Stimulation of the vagus nerve can be easily accomplished with the Valsalva maneuver .

Vagus nerve and heart

The right vagus nerve innervates the sinus node, and its stimulation can cause sinus bradycardia . The left vagus nerve supplies the AV node, and its stimulation can cause heart block . By producing transient heart block, the Valsalva maneuver can interrupt many types of SVT .

The vagus nerve in medical therapy

Because the vagus nerve has so many important functions, medical science has been interested for decades in the idea of using vagus stimulation or block in medical therapy.

For decades, vagotomy (cutting the vagus nerve) has been the mainstay of peptic ulcer therapy because it was a way to reduce the amount of peptic acid produced by the stomach. However, vagotomy has had several side effects and, with the advent of more effective treatments, it is now used less frequently .

At present, there is much interest in the use of electronic pacemakers (essentially modified pacemakers ) for chronic stimulation of the vagus nerve to treat a variety of medical problems. Such devices (commonly called vagus nerve stimulation devices or VNS devices) have been used successfully to treat people with severe drug-resistant epilepsy . VNS therapy is also sometimes used to treat refractory depression .

Because everything looks like a nail when you have a hammer, companies that make VNS devices are investigating their use for other conditions, such as hypertension , migraines, tinnitus , fibromyalgia , and weight loss.

These VNS apps are really promising. However, the true potential of VNS will emerge when advertising is replaced by strong clinical evidence.

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