EXPLAINER

THE BODY’S INFORMATION SUPERHIGHWAY THAT TELLS YOUR ORGANS HOW TO REST

ILLUSTRATIONS: MYRIAM WARES

What is the vagus nerve?

Your brain is connected to your body through a set of 12 crucial nerve networks that descend through your spine and branch out into your body. Of these, the vagus nerve is probably one of the most important. Its tendrils influence digestion, your heart, your reflexes and your breathing. So you can see why scientists are so interested in what it does – especially when you consider how all of the above affect your mood. You could call the vagus nerve a superhighway between our brains and bodies.

In contrast to the rapid ‘fight or flight’ responses that are under the control of the sympathetic arm of the nervous system, the vagus nerve is responsible for many of the slower,

‘rest and digest’ responses that we collectively call the parasympathetic arm. The nerve itself is actually two thick bundles of individual neurons (nerve cells) that originate in the brain and pass out to the rest of the body through left- and right-sided openings at the bottom of the skull.

Most of the individual neurons that make up the vagus nerve are sensory ones – about 100,000 on each side of the body in humans – which pass messages from the organs to the brain, and are activated by sensory input from the environment. The remainder are motor neurons, which send messages in the opposite direction, from the brain to organs, and directly control all of our muscle movements.

Why is the vagus nerve so important?

The vagus nerve is a sort of polymath of the parasympathetic nervous system, getting involved in everything from breathing, heart rate, swallowing, sneezing, digestion, appetite, immune responses and even orgasm. The vagus nerve’s wide-ranging skill set comes from having a diverse array of neuron cell types at its disposal. These allow the nerve to pick up different types of sensory signals from different organs. Some, for instance, sense chemical signals like oxygen levels in the blood or the secretions of bacteria in the intestine, while others sense mechanical signals like stretching of the blood vessels and gut.