It is to Michael Gershon, professor at the University of Columbia in New York, that the intestine owes his nickname “second brain”. But what is this nickname worth it?
First of all, and unlike other organs controlled by the central nervous system, the intestine has its own network of neurons, called an enteric nervous system. This is independent and extends throughout the digestive tract. Concretely, it has several hundred millions of neurons.
The neurons of this separate system come from the same neural tube as the brain, formed in the first weeks of gestation in the fetus. And their structure is also very similar to that of cerebral neurons.
A central role in digestion
But why would we need another brain? A hypothesis is based on the importance of digestion. This function is vital because it provides the body with the energy it needs to work. So to ensure this mission with precision, our body would have this specialized “second brain”.
We now know that this second nervous system pilots several essential functions. Intestinal motor skills, that is to say the contractions that advance foods in the digestive tract, 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 these functions are also implemented independently, without the approval of the brain. This also explains why the intestine deserved this nickname.
A constant dialogue with the brain
This does not mean that it is an isolated organ. On the contrary, it constantly communicates with the central nervous system, in particular via the vagus nerve. And the connection is made in both directions.
For example, stress or intense emotions can influence intestinal functioning that can go as far as causing “a knot in the belly” or diarrhea.
Conversely, certain neurological pathologies could have an intestinal origin. Recent research, for example, suggest that diseases like Parkinson’s disease would start in the intestine before reaching the brain.
Interactions between brain, intestine and intestinal microbiota are today an important and promising research axis.
