The Vagus Nerve

The vagus nerve

The Vagus Nerve
The vagus nerve is depicted in this diagram. The vagus nerve gets its name from the Latin word for wandering, which is fitting given that it is the largest and most widely branching cranial nerve.

 

The vagus nerve is the body’s superhighway, carrying information from the brain to the internal organs and controlling bodily functions during rest and relaxation. The large nerve originates in the brain and branches out in multiple directions to the neck and torso, where it is responsible for actions such as carrying sensory information from the ear skin, controlling the muscles used to swallow and speak, and influencing your immune system.

According to the Encyclopedia Britannica, the vagus nerve is the tenth of twelve cranial nerves that extend directly from the brain.

Although we refer to the vagus nerve as a single nerve, it is actually a pair of nerves that emerge from the left and right sides of the brain stem’s medulla oblongata. According to Merriam-Webster(opens in new tab), the nerve gets its name from the Latin word for wandering, which is appropriate given that the vagus nerve is the largest and most widely branching cranial nerve.

The vagus nerve, which travels and branches throughout the body, provides primary control for the nervous system’s parasympathetic division: the rest-and-digest counterpoint to the sympathetic nervous system’s fight-or-flight response. When the body is not under stress, the vagus nerve sends commands that cause the heart and breathing rates to slow and digestion to increase.

When under stress, control shifts to the sympathetic nervous system, which has the opposite effect.
The vagus nerve also transmits sensory signals from internal organs to the brain, allowing the brain to monitor the organs’ activities.

THE AXIS BRAIN-GUT

 

The vagus nerve has large divisions that extend into the digestive system. According to the textbook “Nerves and Nerve Injuries Volume 1,” 10% to 20% of the vagus nerve cells that connect with the digestive system send commands from the brain to control muscles that move food through the gut (Academic Press, 2015). A separate nervous system embedded within the walls of the digestive system then controls the movement of those muscles.

The remaining 80% to 90% of neurons are responsible for transporting sensory information from the stomach and intestines to the brain. The brain-gut axis is a communication line between the brain and the gastrointestinal tract that keeps the brain informed about the status of muscle contraction, the speed of food passage through the gut, and feelings of hunger or satiety. According to a 2017 study published in the Journal of Internal Medicine(opens in new tab), the vagus nerve is so closely linked to the digestive system that stimulating it can help with irritable bowel syndrome (opens in new tab).

Many researchers have discovered that the bacteria that live inside the intestines have a counterpart to the brain-gut axis.

According to a 2014 review published in the journal Advances in Experimental Medicine and Biology, this microbiome communicates with the brain via the vagus nerve, influencing not only food intake but also mood and inflammation response (opens in new tab). Much of the current research is conducted on mice and rats rather than humans. Nonetheless, the findings are striking, indicating that changes in the microbiome can lead to changes in the brain.

VAGUS NERVE STIMULATION AS A MEDICINE

The vagus nerve has been shown to be effective in treating cases of epilepsy that do not respond to medication. An electrode is wrapped around the right branch of the vagus nerve in the neck, and a battery is implanted below the collarbone.

According to the Epilepsy Foundation, the electrode stimulates the nerve on a regular basis, which reduces or, in rare cases, prevents the excessive brain activity that causes seizures (opens in new tab). According to the Mayo Clinic, Europe has approved a vagus nerve stimulator that does not require surgical implantation (opens in new tab).

Vagus nerve stimulation has also been shown in studies to be effective in treating psychiatric conditions that do not respond to medication. Vagus nerve stimulation has been approved by the FDA for treatment-resistant depression and cluster headaches. A 2008 study published in the journal Brain Stimulation discovered that vagus nerve stimulation improved symptoms in patients suffering from treatment-resistant anxiety disorders such as obsessive-compulsive disorder, panic disorder, and post-traumatic stress disorder.

According to a 2018 review in the Journal of Inflammation Research, researchers have recently been investigating the vagus nerve’s role in treating chronic inflammatory disorders such as sepsis, lung injury, rheumatoid arthritis (RA), and diabetes (opens in new tab). Damage to the vagus nerve, which influences the immune system, may play a role in autoimmune and other disorders.

VAGUS NERVE DEFICIENCY

Chronic conditions such as alcoholism and diabetes have long been known to damage nerves, including the vagus nerve.

If the vagus nerve is damaged, it can cause nausea, bloating, diarrhea, and gastroparesis (when the stomach empties too slowly). According to the Mayo Clinic(opens in new tab), diabetic neuropathy cannot be reversed, and alcoholic neuropathy can also result in permanent nerve damage, according to Healthline (opens in new tab).

If the vagus nerve is damaged due to physical trauma or tumor growth, it can cause digestive symptoms, hoarseness, vocal cord paralysis, and a slowed heart rate. There have been several cases of people whose vagus nerve damage was minor enough that the nerve was able to regenerate after a tumor was removed, including one reported in the journal Neurology in 2011.

FAINTING AND THE VAGUS NERVE

When someone faints as a result of heat exposure, prolonged standing, or something unexpected, such as the sight of blood, the vagus nerve is partially to blame.

According to Cedars Sinai, vasovagal syncope occurs when the sympathetic division dilates blood vessels in the legs and the vagus nerve overreacts, causing a significant and immediate decrease in heart rate (opens in new tab). Blood pools in the legs, blood pressure drops, and the person briefly loses consciousness due to insufficient blood flow to the brain. Vasovagal syncope does not require treatment unless a person faints frequently.

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