Explainer: What is the vagus? | Science News for Students

Explainer: What is the vagus?

This wandering nerve controls many functions, from sweating and heart rate to gagging
Jun 7, 2018 — 6:35 am EST
vagus stimulation

The vagus nerve runs from the base of the brain down the spinal cord, and reaches out to touch most of your organs along the way. The yellow line in this picture is the top of the vagus nerve, here attached to a small electronic stimulator. That device can be used to treat seizures or depression.

Manu5/Wikimedia Commons (CC BY-SA 4.0)

It maintains your heartbeat and makes you sweat. It helps you talk and makes you vomit. It’s your vagus nerve, and it’s the information highway that connects your brain with organs throughout the body.

Vagus is Latin for “wandering.” And this nerve definitely knows how to ramble. It stretches from the brain all the way down the torso. Along the way, it touches key organs, such as the heart and stomach. This gives the vagus control over a huge range of bodily functions.

Most of the cranial (KRAY-nee-ul) nerves — 12 large nerves that leave the base of the brain — reach only a few bits of the body. They might control vision, hearing or the feel of a single finger against your cheek. But the vagus — number 10 out of those 12 nerves — plays dozens of roles. And most of them are functions you never consciously think about, from the feeling inside your ear to the muscles that help you speak.  

The vagus begins in the medulla oblongata (Meh-DU-lah (Ah-blon-GAH-tah). It’s the lowest part of the brain and sits just above where the brain merges into the spinal cord. The vagus is actually two large nerves — long fibers composed of many smaller cells that send information around the body. One emerges on the right side of the medulla, another on the left. But most people refer to both the right and left at the same time when they talk about “the vagus.” 

From the medulla, the vagus moves up, down and around the body. For instance, it reaches up to touch the inside of the ear. Further down, the nerve helps control the muscles of the larynx. That’s the part of the throat containing the vocal cords. From the back of the throat to the very end of the large intestine, parts of the nerve wrap gently around every one of these tubes and organs. It also touches the bladder and sticks a delicate finger into the heart.

Resting and digesting

This nerve’s role is almost as varied as its destinations. Let’s start at the top.

In the ear, it processes the sense of touch, letting someone know if there’s something inside their ear. In the throat, the vagus controls muscles of the vocal cords. This allows people to speak. It also controls the movements of the back of the throat and is responsible for the pharyngeal reflex (FAIR-en-GEE-ul REE-flex). Better known as the gag reflex, it can make someone vomit. More often, this reflex simply helps keep objects from getting caught in the throat where they could make someone choke.

Further down, the vagus nerve wraps around the digestive tract, including the esophagus (Ee-SOF-uh-gus), stomach and the large and small intestines. The vagus controls peristalsis (Pair-ih-STAHL-sis) — the wavelike contraction of muscles that move food through the gut.

Most of the time, it would be easy to ignore your vagus. It’s a large part of what’s called the parasympathetic nervous system. That’s a long term to describe that part of the nervous system that controls what happens without our thinking about it. It helps the body do things that it’s put off for when it’s relaxed, such as digesting food, reproducing or peeing.

When turned on, the vagus nerve can slow the heart’s beating and lower blood pressure. The nerve also reaches into the lungs where it helps to control how fast you breathe. The vagus even controls the smooth muscle that contracts the bladder when you pee. As noted earlier, it regulates sweating, too.

This nerve can even make people faint. Here’s how: When someone is extremely stressed, the vagus nerve can get overstimulated as it works to bring down heart rate and blood pressure. This may cause someone’s heartbeat to slow down too much. Blood pressure may now plummet. Under these conditions, too little blood reaches the head — causing someone to faint. This is called vasovagal syncope (Vay-zoh-VAY-gul SING-kuh-pee).

The vagus isn’t a one-way street. It’s really more like a two-way, six-lane superhighway. This nerve sends signals out of the brain, then receives feedback from outposts throughout body. Those cellular tips go back to the brain and allow it to keep tabs on each organ the vagus touches.

Information from the body not only can change how the brain controls the vagus, but can also affect the brain itself. These information exchanges include signals from the gut. Bacteria in the gut can produce chemical signals. These can act on the vagus nerve, shooting signals back to the brain. This may be one way that bacteria in the gut can influence mood. Stimulating the vagus directly has even been shown to treat some cases of severe depression.

Power Words

(for more about Power Words, click here)

bacterium (plural bacteria)  A single-celled organism. These dwell nearly everywhere on Earth, from the bottom of the sea to inside animals.

blood pressure  The force exerted against vessel walls by blood moving through the body. Usually this pressure refers to blood moving specifically through the body’s arteries. That pressure allows blood to circulate to our heads and keeps the fluid moving so that it can deliver oxygen to all tissues. Blood pressure can vary based on physical activity and the body’s position. High blood pressure can put someone at risk for heart attacks or stroke. Low blood pressure may leave people dizzy, or faint, as the pressure becomes too low to supply enough blood to the brain.

cranial nerves     A set of 12 pairs of nerves in mammals that connects the brain directly to muscles and organs of the head and torso.

cranium   The part of the skull that protects the brain. Used as an adjective, the term would be cranial.

depression  A mental illness characterized by persistent sadness and apathy. Although these feelings can be triggered by events, such as the death of a loved one or the move to a new city, that isn’t typically considered an “illness” — unless the symptoms are prolonged and harm an individual’s ability to perform normal daily tasks (such as working, sleeping or interacting with others). People suffering from depression often feel they lack the energy needed to get anything done. They may have difficulty concentrating on things or showing an interest in normal events. Many times, these feelings seem to be triggered by nothing; they can appear out of nowhere.

digestive tract    The tissues and organs through which foods enter and move through the body. These organs include the esophagus, stomach, intestines, rectum and anus. Foods are digested — broken down — and absorbed along the way. Any materials not used will exit as wastes (feces and urine).

epilepsy    A neurological disorder characterized by seizures.

esophagus    The tube at the top of the digestive tract through which food moves from the throat to the stomach.

larynx  The hollow, muscular organ forming an air passage to the lungs and holding the vocal cords in humans and other mammals. It’s also known as the voice box.

medulla oblongata    The lowest portion of the brain in mammals. This area helps to regulate basic involuntary functions such as breathing and heart rate. 

nerves  Long, delicate fibers that communicate across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold, pain.

nervous system  The network of nerve cells and fibers that transmits signals between parts of the body.

neuron or nerve cell     Any of the impulse-conducting cells that make up the brain, spinal column and nervous system. These specialized cells transmit information to other neurons in the form of electrical signals.

parasympathetic nervous system     This is a part of the nervous system that is associated with functions called “rest and digest.” These are activities an organism carries out when it is at rest, such as digesting, peeing, pooping, drooling, crying and breeding.

peristalsis    The wave-like muscle contractions that push food through the digestive tract.

pharyngeal reflex    Also known as the gag reflex. It describes an involuntary contraction in the back of the throat that is stimulated when you touch the back of the tongue, throat or mouth. It often results in vomiting. This reflex is one way the body keeps foreign objects out of the throat and lungs.

vagus      A large nerve that conducts signals between the brain and organs throughout the body (notably the stomach and intestines).

vasovagal syncope     A type of fainting that occurs when there is not enough blood getting to the brain. It usually occurs during times of extreme stress, when the vagus nerve is overstimulated. The vagus nerve may signal the heart to beat too slowly and to reduce blood pressure too much. That’s what leads to fainting.

vocal cords    A pair of membranes that are stretched over the opening of the larynx. They open when someone inhales air. They close when an animal holds his or her breath. But most importantly, they provide sounds — the voices — of animals. This happens as they vibrate when air is expelled from the lungs and squeezed through them. Animals can control the tension in these membranes, and how much they open. This provides the pitch of a sound and how loud it is, from a whisper to a bellow.