Anatomy of the Vagus Nerve

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The vagus nerve, also known as the tenth cranial nerve or cranial nerve X, is the longest nerve of the autonomic nervous system which controls involuntary body functions. The vagus nerve is tasked with regulating critical body functions such as heart rate, blood pressure, breathing, and digestion.

The malfunctioning of the vagus nerve can undermine these and other involuntary body functions, referred to as autonomic dysfunction or dysautonomia,

There are tests that can help determine how effectively the vagus nerve is working and procedures (like vagus nerve stimulation) that can help treat neurological disorders like epilepsy and depression.

This article looks at the anatomy and function of the vagus nerve as well as medical conditions that can affect it. It also explores the effectiveness of vagus nerve stimulation and where the procedure may prove useful.

Anatomy and Function of the Vagus Nerve

The vagus nerve is one of 12 cranial nerves. It is a long nerve that originates in the brain stem and extends through the neck and into the chest and abdomen. While there are actually two vagus nerves (a left and a right), they are referred to collectively as “the vagus nerve.”

It is the main nerve of the parasympathetic nervous system. The autonomic nervous system is made up of the parasympathetic system, which controls "rest and digest" functions, and the sympathetic nervous system, which handles "fight or flight" responses. The two parts are often thought of as being opposites of each other.

The vagus nerve carries motor and sensory information to different organ systems of the body, including:

The vagus nerve transports nerve signals to the brain to regulate involuntary functions like heart rate, respiration, blood pressure, and peristalsis (the wave-like contraction of muscles that move food through the digestive tract).

The vagus nerve also provides sensory information to the skin and muscles which, in turn, stimulates reflex actions like coughing, sneezing, swallowing, gagging, and vomiting. The sensory information also stimulates body functions like sweating, salivating, mucus production, and the urge to urinate.

Vagus Nerve and the Gut-Brain Axis

The vagus nerve also forms a link between the gut and the brain, known as the brain-gut axis. In recent years, scientists have established a link between the dysfunction of the brain-gut axis and conditions like obesity, epilepsy, and depression.

Doctor examining patient in office
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Vagus Nerve Disorders

There are many conditions that can damage the vagus nerve, including alcoholism, diabetes, benign or cancerous tumors, and physical trauma. On the flip side, there are numerous conditions caused or influenced by vagus nerve dysfunction, the underlying cause of which may be unknown.

Problems with the vagus nerve referred to as vagopathies can cause a variety of symptoms depending on which part of the nerve is affected.

Among the conditions associated with vagopathy are:

  • Acid reflux: This is when stomach acids backflow into the esophagus (feeding tube), including a chronic form of the condition known as gastroesophageal reflux disease (GERD).
  • Cardiac arrhythmia: This is an irregular heartbeat. It may also include bradycardia (an abnormally slowed heartbeat), tachycardia (an abnormally rapid heartbeat), and palpitations (skipped heartbeat).
  • Dysphagia: This is difficulty swallowing foods or liquids.
  • Gastroparesis: This is a digestive disorder in which food does not move properly from the stomach into the intestines, causing abdominal pain and bloating.
  • Laryngopathy: This is the dysfunction of the larynx (voice box) which can lead to hoarseness and speech problems.
  • Orthostatic hypotension: This is dizziness or fainting caused by a rapid drop in blood pressure while standing or rising.
  • Singultus: This is another name for hiccups.
  • Vasovagal syncope: This is fainting caused by a sudden and strong emotional response, such as being frightened or seeing blood. Other symptoms include ringing in the ears, tunnel vision, and nausea.

Testing the Vagus Nerve

Diagnosing vagus nerve dysfunction can be difficult as the damage can occur anywhere along the length and branches of the nerve.

One simple but effective way to test the vagus nerve is by checking the gag reflex. This involves tickling the back of the throat with a soft cotton swab. If the person doesn't gag, it could indicate a problem at the brainstem where the vagus nerve originates.

Additional tests may be ordered to check for possible vagus nerve damage or deterioration or damage:

  • Doppler ultrasound: This non-invasive imaging tool uses sound waves to detect thinning of the vagus nerves of the neck. It can also check for abnormalities in the blood vessels that service the vagus nerves of the neck.
  • Valsalva maneuver: This is a test in which you exhale forcefully while keeping your nose and mouth tightly shut. It is used to see how your heart responds to the change in pressure and may detect abnormalities suggestive of autonomic dysfunction.
  • Skin conductance response: This uses a device that can detect whether sweat is produced when a person is placed under stress. An electrocardiogram (ECG) may be used simultaneously to see if your heart rate changes.

Other tests may be ordered to characterize your symptoms or help narrow the possible causes.

Vagus Nerve Stimulation

Vagus nerve stimulation (VNS) is a medical treatment in which electrical impulses are sent to the vagus nerve to treat epilepsy or major depressive disorder (MDD).

Both epilepsy and MDD are thought to be caused by the dysfunction of the brain-gut axis in which the vagus nerve plays a central role. Dysfunction of the brain-gut axis can lead to the overgrowth of microbes in the digestive tract that directly interferes with brain function, increasing the risk of seizures and depression.

VNS involves a device that is strapped around your chest that delivers gentle electrical impulses that "re-synchronize" nerve signals between the brain and gut so that they function more normally.

In the United States, VNS is approved as an add-on therapy for people 4 years and older with treatment-resistant focal seizures.

How Effective Is VNS?

Studies have shown that VNS reduces the frequency of epileptic seizures by 51% after one year of therapy. While the effectiveness of VNS for depression is harder to establish, the current body of evidence suggests that it is well-tolerated and potentially beneficial but that further research is needed.

VNS is being explored for other conditions influenced by autonomic dysfunction, including obesity, hypertension (high blood pressure), anxiety disordersheart failure, cardiac arrhythmias, Alzheimer's disease, and Parkinson's disease.

Natural Vagus Nerve Treatments

For those who do not have access to a VNS device or want a more natural approach to treatment, there are practices that some contend may help manage autonomic dysfunction.

These at-home treatments are thought to stimulate the vagus nerve by slowing the heart rate and reducing emotional stresses that can trigger or worsen vagus nerve disorders.

Examples include:

  • Deep breathing exercises: Slow, conscious breathing is thought to stimulate the vagus nerve, not only improving heart rate and blood pressure but also easing digestion.
  • Mindfulness exercises: These include practices like yoga and tai chi in which respiration is synchronized with body movements. Some studies suggest such practices can improve vagal nerve tone, leading to a slower heart rate and lower blood pressure.
  • Foot reflexology: This massage-based practice has been shown to slow heart rate and respiration, lower blood pressure, and increase oxygen saturation, suggesting that it positively stimulates the vagus nerve.
  • Music therapy: It is thought certain types of music can positively influence moods and elicit a beneficial autonomic response. This may be especially true with low-frequency sounds delivered with slow, rhythmically structured music.
  • Cold-water immersion: Facial immersion in cold water is thought to indirectly stimulate the vagus nerve. This is evidenced by the fact that, after the initial shock of cold, the heart rate will begin to slow. Open-water swimming may have the same effect.

It is unclear whether any of these techniques directly stimulate the vagus nerve in the same way as electrical VMS, but each is known to trigger a positive physiological response that can help relieve stress and improve moods.

11 Sources
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By Richard N. Fogoros, MD
Richard N. Fogoros, MD, is a retired professor of medicine and board-certified in internal medicine, clinical cardiology, and clinical electrophysiology.