The vagus nerve is the longest and most complex of the 12 pairs of cranial nerves that emanate from the brain. It transmits information to or from the surface of the brain to tissues and organs elsewhere in the body.
The name "vagus" comes from the Latin term for "wandering." This is because the vagus nerve wanders from the brain into organs in the neck, chest, and abdomen.
It is also known as the 10th cranial nerve or cranial nerve X.
The vagus nerve has two bunches of sensory nerve cell bodies, and it connects the brainstem to the body. It allows the brain to monitor and receive information about several of the body's different functions.
There are multiple nervous system functions provided by the vagus nerve and its related parts. The vagus nerve functions contribute to the autonomic nervous system, which consists of the parasympathetic and sympathetic parts.
The nerve is responsible for certain sensory activities and motor information for movement within the body.
Essentially, it is part of a circuit that links the neck, heart, lungs, and the abdomen to the brain.
What does the vagus nerve affect?
The vagus nerve has a number of different functions. The four key functions of the vagus nerve are:
- Sensory: From the throat, heart, lungs, and abdomen.
- Special sensory: Provides taste sensation behind the tongue.
- Motor: Provides movement functions for the muscles in the neck responsible for swallowing and speech.
- Parasympathetic: Responsible for the digestive tract, respiration, and heart rate functioning.
Its functions can be broken down even further into seven categories. One of these is balancing the nervous system.
The nervous system can be divided into two areas: sympathetic and parasympathetic. The sympathetic side increases alertness, energy, blood pressure, heart rate, and breathing rate.
The parasympathetic side, which the vagus nerve is heavily involved in, decreases alertness, blood pressure, and heart rate, and helps with calmness, relaxation, and digestion. As a result, the vagus nerve also helps with defecation, urination, and sexual arousal.
Other vagus nerve effects include:
- Communication between the brain and the gut: The vagus nerve delivers information from the gut to the brain.
- Relaxation with deep breathing: The vagus nerve communicates with the diaphragm. With deep breaths, a person feels more relaxed.
- Decreasing inflammation: The vagus nerve sends an anti-inflammatory signal to other parts of the body.
- Lowering the heart rate and blood pressure: If the vagus nerve is overactive, it can lead to the heart being unable to pump enough blood around the body. In some cases, excessive vagus nerve activity can cause loss of consciousness and organ damage.
- Fear management: The vagus nerve sends information from the gut to the brain, which is linked to dealing with stress, anxiety, and fear - hence the saying, "gut feeling." These signals help a person to recover from stressful and scary situations.
Stimulation of the vagus nerve is a medical procedure that is used to try to treat a variety of conditions. It can be done either manually or through electrical pulses.
The effectiveness of vagus nerve stimulation has been tested through clinical trials. Consequently, the United States Food and Drug Administration (FDA) has approved its use to treat two different conditions.
In 1997, the FDA allowed the use of vagus nerve stimulation for refractory epilepsy.
This involves a small, electrical device, similar to a pacemaker, being placed in a person's chest. A thin wire known as a lead runs from the device to the vagus nerve.
The device is placed in the body by surgery under general anesthetic. It then sends electrical impulses at regular intervals, throughout the day, to the brain via the vagus nerve to reduce the severity, or even stop, seizures.
Side effects of vagus nerve stimulation for epilepsy include:
- hoarseness or changes in voice
- sore throat
- shortness of breath
- slow heart rate
- difficulty swallowing
- stomach discomfort or nausea
People using this form of treatment should always tell their doctor if they are having any problems as there may be ways to reduce or stop these.
With the vagus nerve having pathways to almost every organ in the body, researchers are looking to see if stimulation can help other conditions.
These conditions include:
- rheumatoid arthritis inflammation
- heart failure
- inflammation from diabetes mellitus
- intractable hiccups
- abnormal heart rhythm
- inflammation from Crohn's disease
In the case of rheumatoid arthritis, which affects 1.3 million adults in the U.S., a study in 2016 showed that vagus nerve stimulation could help reduce symptoms. Individuals who had failed to respond to other treatment reported significant improvements, while no serious adverse side effects were noted.
This was considered a real breakthrough in how vagus nerve stimulation might not only treat rheumatoid arthritis but other inflammatory diseases, such as Crohn's, Parkinson's, and Alzheimer's.