Scientific American | By Adam Hadhazy | February 12, 2010
"Technically known as the enteric nervous system, the second brain consists of sheaths of neurons embedded in the walls of the long tube of our gut, or alimentary canal, which measures about nine meters end to end from the esophagus to the anus. The second brain contains some 100 million neurons, more than in either the spinal cord or the peripheral nervous system, Gershon says."
The second brain informs our state of mind in other more obscure ways, as well. "A big part of our emotions are probably influenced by the nerves in our gut," Mayer says. Butterflies in the stomach—signaling in the gut as part of our physiological stress response, Gershon says—is but one example.
(...) in fact 95 percent of the body's serotonin is found in the bowels. Because antidepressant medications called selective serotonin reuptake inhibitors (SSRIs) increase serotonin levels, it's
little wonder that meds meant to cause chemical changes in the mind often provoke GI issues as a side effect. Irritable bowel syndrome—which afflicts more than two million Americans—also arises in
part from too much serotonin in our entrails, and could perhaps be regarded as a "mental illness" of the second brain.
Information from Scholarpedia by the author of the article cited below
Image 1 for ENS
The following image shows the gastrointestinal tract on the left (from esophagus to anus) with different kinds of ENS (enteric nervous system) neurons in blue, purple and red.
Figure 1 | The innervation of the gastrointestinal tract.
The digestive system contains full reflex circuits of the ENS (motor neurons and interneurons in blue,
sensory neurons in purple).
Pathways from the gastrointestinal tract project outwards, via intestinofugal neurons (red), to the CNS (neurons in yellow), sympathetic ganglia, gallbladder and pancreas.
Abbreviations: CNS, central nervous system; ENS, enteric nervous system.
Source: Furness, J. B. (2012) The enteric nervous system and neurogastroenterology Nat. Rev. Gastroenterol. Hepatol. doi:10.1038/nrgastro.2012.32
Image 2 for ENS
Images from scientific study with labelings of the enteric system
Reading notes from the article “L’intelligence du ventre” by Miriam Gablier published on 2014-01-21 http://www.inrees.com/articles/intelligence-du-ventre/
It has recently been discovered that we have other “brains” in our body. A neural nebula of 40000 neurons is found at the level of our heart. But another complex of 100 million neurons minimum is
found in our intestines. As Dr. Gershon mentions this is only 1000 times smaller than that of our brain. This is called the Enteric Nervous System. [Comments from Dr. Gershon follow]. It does not
necessarily follow commands from the brain or the spinal cord and neither does it send them the information it collects; it can act independently when it chooses to do so. Except for digestion and
nutrient absorption, the intestines also protect us from hostile bacteria attacks. It is therefore logical that evolution has created a specific brain for these important tasks. There is a need for
such a large number of neural cells to do these tasks that if those were to be connected to the head, the weight of the neuronal cable connections would be intolerable. It is considered that it is
best to leave the intestines take care of these things.
Since the enteric nervous system can function on its own, it is possible that it has “its own neuroses”? Is this why our intestines react so intensely to particularly stressful conditions? Cramps, bloating, diarrhea, constipation…Our instinctive reactions, which we call visceral or gut reactions could put a toll on our belly. It is our unconscient procedures that regulate our survival; as the neurologist B. Libet says, conscience is late by “half of a second” compared to reality. We cannot leave processes that are fundamental to our survival being regulated by conscious control.
Can the enteric system solve its problems? It is an important organ of elimination and by specific techniques of massage and relaxation we could enhance this capacity.
It manages our instinct, it provides unconscious information and regulates our mood? It also seems to have perception abilities. Researchers D.Radin and M.Schlitz using electrogastrography (EGG) and a skin galvanometer for stomach measurements asked volunteers to view on a screen specific representations that induce different emotions such as sadness or affection while at the same time viewing on another screen another individual. The EEG of the last ones were higher than those of controls and showed correlations to those of the volunteers that viewed the representations.
"This squeezing of the muscular walls is termed peristalsis and involves a ring of contraction moving aborally (away from the oral cavity) towards the anus a few inches at a time."
Three contraction waves per minute for the stomach, twelve for the small intestine.