There are 12 cranial nerves in the body. They come in pairs and help to link the brain with other areas of the body, such as the head, neck, and torso.
Some send sensory information, including details about smells, sights, tastes, and sounds, to the brain. These nerves are known as having sensory functions. Other cranial nerves control the movement of various muscles and the function of certain glands. These are known as motor functions.
While some cranial nerves have either sensory or motor functions, others have both. The vagus nerve is such a nerve. The cranial nerves are classified using Roman numerals based off of their location. The vagus nerve is also called cranial nerve X.
The word “vagus” means wandering in Latin. This is a very appropriate name, as the vagus nerve is the longest cranial nerve. It runs all the way from the brain stem to part of the colon.
The sensory functions of the vagus nerve are divided into two components:
- Somatic components. These are sensations felt on the skin or in the muscles.
- Visceral components. These are sensations felt in the organs of the body.
Sensory functions of the vagus nerve include:
- providing somatic sensation information for the skin behind the ear, the external part of the ear canal, and certain parts of the throat
- supplying visceral sensation information for the larynx, esophagus, lungs, trachea, heart, and most of the digestive tract
- playing a small role in the sensation of taste near the root of the tongue
Motor functions of the vagus nerve include:
- stimulating muscles in the pharynx, larynx, and the soft palate, which is the fleshy area near the back of the roof of the mouth
- stimulating muscles in the heart, where it helps to lower resting heart rate
- stimulating involuntary contractions in the digestive tract, including the esophagus, stomach, and most of the intestines, which allow food to move through the tract
To test the vagus nerve, a doctor may check the gag reflex. During this part of the examination, the doctor may use a soft cotton swab to tickle the back of the throat on both sides. This should cause the person to gag. If the person doesn’t gag, this may be due to a problem with the vagus nerve.
Damage to the vagus nerve can have a range of symptoms because the nerve is so long and affects many areas.
Potential symptoms of damage to the vagus nerve include:
- difficulty speaking or loss of voice
- a voice that is hoarse or wheezy
- trouble drinking liquids
- loss of the gag reflex
- pain in the ear
- unusual heart rate
- abnormal blood pressure
- decreased production of stomach acid
- nausea or vomiting
- abdominal bloating or pain
The symptoms someone might have depend on what part of the nerve is damaged.
Experts believe that damage to the vagus nerve may also cause a condition called gastroparesis. This condition affects the involuntary contractions of the digestive system, which prevents the stomach from properly emptying.
Symptoms of gastroparesis include:
- nausea or vomiting, especially vomiting undigested food hours after eating
- loss of appetite or feeling full shortly after starting a meal
- acid reflux
- abdominal pain or bloating
- unexplained weight loss
- fluctuations in blood sugar
Some people develop gastroparesis after undergoing a vagotomy procedure, which removes all or part of the vagus nerve.
Sometimes the vagus nerve overreacts to certain stress triggers, such as:
- exposure to extreme heat
- fear of bodily harm
- the sight of blood or having blood drawn
- straining, including trying to having a bowel movement
- standing for a long time
Remember, the vagus nerve stimulates certain muscles in the heart that help to slow heart rate. When it overreacts, it can cause a sudden drop in heart rate and blood pressure, resulting in fainting. This is known as vasovagal syncope.
Vagus nerve stimulation involves placing a device in the body that uses electrical impulses to simulate the nerve. It’s used to treat some cases of epilepsy and depression that don’t respond to other treatments.
The device is usually placed under the skin of the chest, where a wire connects it to the left vagus nerve. Once the device is activated, it sends signals through the vagus nerve to your brainstem, which then transmits information to your brain. A neurologist usually programs the device, but people often receive a handheld magnet they can use to control the device on their own as well.