The vagus nerve runs from the brain throughout the head and body, issuing commands to organs and receiving sensations from them.
Imagine a person walking alone on a street late at night when they hear footsteps behind them. This person will feel their heart racing, blood pressure skyrocketing, goosebumps rising on their arms, palms sweating, stomach churning, and muscles tightening, ready to either sprint away or fight. Such experiences highlight the tight connection between the brain and body. So, how is this connection organized?
The vagus nerve affects human responses when in fear. (Image: Whistlesforlife)
The answer lies in the vagus nerve. This is the longest nerve in the body, extending from the brain to the head and torso, issuing commands to various organs and receiving sensory information from them. Most of the functions it regulates, such as mood, learning, and fear, are automatic and operate without conscious control.
Ancient anatomists were aware of the vagus nerve, notably Galen, a Greek scholar who died around 216 AD. However, it took scientists centuries of research to understand its complex function and anatomy. This effort is still ongoing today.
The vagus nerve originates from four clusters of nerve cells in the brainstem, where the brain connects to the spinal cord. Most nerves in the human body branch directly from the spinal cord, but the vagus nerve does not. It is one of 13 nerves that exit the brain directly through special openings in the skull. From there, it grows branches that reach nearly everywhere in the head and torso.
The vagus nerve also extends from two large clusters of nerve cells known as ganglia, located at critical points in the body. For instance, there is a large cluster of vagus nerve cells that cling like vines to the carotid artery in the neck. The nerve fibers follow the network of blood vessels throughout the body to reach vital organs like the heart, lungs, and intestines.
Every complex system in the body needs equivalent components for braking and acceleration to maintain control. The vagus nerve plays such a role in many of human beings’ innate responses. Signals between the brainstem and the body travel up and down the vagus nerve to contract the intestines during digestion, regulate the immune system to fend off bacterial threats, adjust heart rate, and increase or decrease blood pressure. The vagus nerve also constricts the bronchial tubes to bring air into the lungs, triggers the gag reflex, and induces coughing.
The vagus nerve stretches from the brain to the entire body and governs various organs. (Image: Sally Caulwell/Quanta Magazine).
The primary function of the vagus nerve is to dampen the body’s response. For example, after a moment of fear, the body’s intense reaction needs to be halted to restore heart rate, breathing, blood flow… to normal levels. The influence of the vagus nerve is so strong that it can even stop a racing heartbeat. Conversely, this nerve can also stimulate the body’s response by “releasing the brake” to speed up.
The “braking” effect of the vagus nerve serves as the biological basis for new therapies that stimulate the nerve to suppress seizures, reduce anxiety disorders, alleviate inflammatory responses, prevent migraines, and many other potential therapies. Unlike deep brain stimulation methods used to treat similar conditions, vagus nerve stimulation can occur without the need for neurosurgery.
For instance, nerve fibers can be stimulated with mild electrical pulses by placing electrodes in the chest or, more simply, by clipping them to the ear. This technique has been used to treat epilepsy and depression for decades. In 2021, the U.S. Food and Drug Administration (FDA) also approved this technique for treating movement issues caused by stroke.
Without the vast reach and powerful influence of the longest nerve, the crucial, tight link between the brain and body would be disrupted, and many core emotions and experiences – fear, joy, quick reactions to threats, and the ability to regain calm afterward – would be impaired. Therefore, even without being a cure-all, the vagus nerve remains incredibly noteworthy.
