Health. Intestine: Why is it called the “second brain”?

Michael Gershon, a professor at Columbia University in New York, is credited with giving the gut its nickname of "second brain." But what does this nickname mean?

First, unlike other organs controlled by the central nervous system, the intestine has its own network of neurons, called the enteric nervous system. This is independent and extends throughout the digestive tract. Specifically, it has several hundred million neurons.

The neurons in this separate system originate from the same neural tube as the brain, which forms in the fetus during the first weeks of gestation. Their structure is also very similar to that of brain neurons.

A central role in digestion

But why would we need another brain? One hypothesis is based on the importance of digestion. This function is vital because it provides the body with the energy it needs to function. So, to carry out this mission with precision, our body would be equipped with this specialized "second brain."

We now know that this second nervous system controls several essential functions. Intestinal motility, that is, the contractions that move food through the digestive tract, the secretion of enzymes, hormones, and mucus necessary for digestion and protection of the mucous membrane, as well as the detection of harmful substances and the activation of defense reactions.

All of these functions are implemented autonomously, without the brain's approval. This also explains why the intestine earned this nickname.

A constant dialogue with the brain

This does not mean, however, that it is an isolated organ. On the contrary, it communicates constantly with the central nervous system, notably via the vagus nerve. And the connection goes in both directions.

For example, stress or intense emotions can influence intestinal function, even causing "a knot in the stomach" or diarrhea.

Conversely, some neurological pathologies may have an intestinal origin. Recent research suggests, for example, that diseases such as Parkinson's disease begin in the gut before reaching the brain.

The interactions between the brain, intestine and intestinal microbiota currently constitute an important and promising area of research.