Adam Hadhazy, wrote last year, in Scientific American, Think Twice: How the Gut's "Second Brain" Influences Mood and Well-Being: The emerging and surprising view of how the enteric nervous system in our bellies goes far beyond just processing the food we eat A '"network of neurons lining our guts ... is so extensive some scientists have nicknamed it our "second brain"".
Image: ISTOCKPHOTO/ERAXION
A deeper understanding of this mass of neural tissue, filled with important neurotransmitters, is revealing that it does much more than merely handle digestion or inflict the occasional nervous pang. The little brain in our innards, in connection with the big one in our skulls, partly determines our mental state and plays key roles in certain diseases throughout the body. ...
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.
Graphic Credit New York Times
Adam Hadhazy continues:
This multitude of neurons in the enteric nervous system enables us to "feel" the inner world of our gut and its contents. Much of this neural firepower comes to bear in the elaborate daily grind of digestion. Breaking down food, absorbing nutrients, and expelling of waste requires chemical processing, mechanical mixing and rhythmic muscle contractions that move everything on down the line. ...
For example, scientists were shocked to learn that about 90 percent of the fibers in the primary visceral nerve, the vagus, carry information from the gut to the brain and not the other way around. "Some of that info is decidedly unpleasant," Gershon says. ...
"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. Although gastrointestinal (GI) turmoil can sour one's moods, everyday emotional well-being may rely on messages from the brain below to the brain above.
Given the two brains' commonalities, other depression treatments that target the mind can unintentionally impact the gut. The enteric nervous system uses more than 30 neurotransmitters, just like the brain, and in fact 95 percent of the body's serotonin is found in the bowels. ...
Cutting-edge research is currently investigating how the second brain mediates the body's immune response; after all, at least 70 percent of our immune system is aimed at the gut to expel and kill foreign invaders. ...
U.C.L.A.'s Mayer is doing work on how the trillions of bacteria in the gut "communicate" with enteric nervous system cells (which they greatly outnumber). His work with the gut's nervous system has led him to think that in coming years psychiatry will need to expand to treat the second brain in addition to the one atop the shoulders.
Maybe the old adage that the best way to a man's heart is through his stomach was not just an old wives tell. It appears to be a superhighwy to to our brains as well.
6:59 AM PT: http://en.wikipedia.org/...
The ENS is capable of autonomous functions[3] such as the coordination of reflexes; although it receives considerable innervation from the autonomic nervous system it can and does operate independently of the brain and the spinal cord.[4] Its study is the focus of neurogastroenterology. The ENS can be damaged by ischemia.[5] Transplantation has been described as a theoretical possibility.[6]
The enteric nervous system has been described as a "second brain".[10] There are several reasons for this. The enteric nervous system can operate autonomously. It normally communicates with the central nervous system (CNS) through the parasympathetic (e.g., via the vagus nerve) and sympathetic (e.g., via the prevertebral ganglia) nervous systems. However, vertebrate studies show that when the vagus nerve is severed, the enteric nervous system continues to function.
In vertebrates the enteric nervous system includes efferent neurons, afferent neurons, and interneurons, all of which make the enteric nervous system capable of carrying reflexes and acting as an integrating center in the absence of CNS input. There are more nerve cells in the enteric nervous system than in the entire spinal cord. The sensory neurons report on mechanical and chemical conditions. Through intestinal muscles, the motor neurons control peristalsis and churning of intestinal contents. Other neurons control the secretion of enzymes. The enteric nervous system also makes use of more than 30 neurotransmitters, most of which are identical to the ones found in CNS, such as acetylcholine, dopamine, and serotonin. More than 90% of the body's serotonin lies in the gut, and about 50% of the body's dopamine lies in the gut as well, and is now being studied to understand the working of the dopamine in the brain.[11]
7:24 AM PT: This article is from 2005, but for those really interested, especially about IBS, it is worth a read, as it is a 4 page article.
http://www.nytimes.com/...
The Other Brain Also Deals With Many Woes
By HARRIET BROWN
Published: August 23, 2005
Keith Meyers/The New York Times
Dr. Michael Gershon studies brain-gut connections.
The Brain in Your Gut
In fact, anyone who has ever felt butterflies in the stomach before giving a speech, a gut feeling that flies in the face of fact or a bout of intestinal urgency the night before an examination has experienced the actions of the dual nervous systems.
The connection between the brains lies at the heart of many woes, physical and psychiatric. Ailments like anxiety, depression, irritable bowel syndrome, ulcers and Parkinson's disease manifest symptoms at the brain and the gut level.
"The majority of patients with anxiety and depression will also have alterations of their GI function," said Dr. Emeran Mayer, professor of medicine, physiology and psychiatry at the University of California, Los Angeles.
One system's symptoms - and cures - may affect the other. Antidepressants, for example, cause gastric distress in up to a quarter of the people who take them. Butterflies in the stomach are caused by a surge of stress hormones released by the body in a "fight or flight" situation. Stress can also overstimulate nerves in the esophagus, causing a feeling of choking.
Dr. Gershon, who coined the term "second brain" in 1996, is one of a number of researchers who are studying brain-gut connections in the relatively new field of neurogastroenterology. New understandings of the way the second brain works, and the interactions between the two, are helping to treat disorders like constipation, ulcers and Hirschprung's disease.
"What brains do is control behavior," Dr. Wood said. "The brain in your gut has stored within its neural networks a variety of behavioral programs, like a library. The digestive state determines which program your gut calls up from its library and runs."
Serotonin also acts as a go-between, keeping the brain in the skull up to date with what is happening in the brain below. Such communication is mostly one way, with 90 percent traveling from the gut to the head.
Serotonin is also implicated in one of the most debilitating gut disorders, irritable bowel syndrome, or I.B.S., which causes abdominal pain and cramping, bloating and, in some patients, alternating diarrhea and constipation.
He said up to 70 percent of the patients he treats for chronic gut disorders had experienced early childhood traumas like parents' divorces, chronic illnesses or parents' deaths. "I think that what happens in early life, along with an individual's genetic background, programs how a person will respond to stress for the rest of his or her life," he said.