In recent years, the vagus nerve has become more well-known than ever before, as it has become a golden target for many chronic disease therapies. What is the vagus nerve? And what does it do, and why is it so important to our health?

For centuries, the vagus nerve (also called the cranial nerve X or 10th cranial nerve) has been an epicenter in medical research. From the work of Galen, a Greek physician and philosopher in the second century, scientists first discovered the existence of the vagus nerve as one of the 12 cranial nerves in the autonomic nervous system. (A cranial nerve is simply a nerve that begins in the brain.) Since then, contributions of the vagus nerve to the physiology of health and disease have been widely studied.

Vagus comes from a Latin word that means “wandering.” Living up to its name, the vagus nerve wanders from the brainstem down to our chest and abdominal cavities, and supplies nerves to major organs such as the heart, lungs, gut, spleen, pancreas and liver.

The vagus nerve acts like a telephone for your brain. It connects the body and the brain, allowing a seamless information transfer in and out of the brain, from and to different areas of the body.

Built to sense and carry, the vagus nerve is equipped with input (sensory) and output (motor) arms. About 80% of the vagus nerve is made up of sensory nerve cells (neurons) that detect mechanical, chemical or even thermal signals generated in the body. When activated by these signals, vagal sensory neurons deliver information from these signals to the brain. Then, further processing occurs to regulate physiological responses that maintain a balance of bodily function.

One example of the profound role of the vagal sensory neurons is sensing food-related signals from the gut, such as how our stomach stretches when filled with food. This information is then transmitted to the brain to regulate our appetite.

About 20% of the vagus nerve’s job is keeping our health in check by carrying commands from the brain to our organs through its motor neurons. One of the roles of the vagal motor neurons is regulating vital functions such as heart rate. When activated, vagal motor neurons send signals to slow down our heart rate, which is paramount in exercise and in the event of a heart attack.

Many diseases can change vagus nerve activity. In obesity, for example, vagal sensory neurons are less sensitive to meal-related signals. In cardiovascular disease, vagal motor neurons tend to be underactive. Despite knowing this, scientists still do not have a full understanding of whether dysfunction of the vagus nerve is a cause or a consequence of a disease.

Researchers still have so much more to do to unlock the full potential of this wandering nerve—with its strong brain-body connection and fundamental role in physiology—to help develop better treatments for better health.