Two brains are better than one, especially if you're hungry
Ever had diarrhea when you felt frightened? Had a stomach cramp before an important exam? Seen a snake barf a beetle meal when surprised?
If you've answered 'yes' to any question in this little quiz, you've already noticed the handiwork of an obscure piece of neurological networking called the enteric (defined) nervous system.
(On the other hand, if you answered a string of "no's," were you entirely candid -- or awake?)
Scientists who study the network of nerves surrounding the esophagus, stomach and intestines compare it to a microcomputer, and call the better-known brain-in-the-head a "mainframe." But while microcomputers represent the future of silicon processing, this biological micro-in-the-belly is a relic of the distant past, of a time when the most important thing in life was eating.
(So that's why they talk about the good ol' days...)
Millions of years before the dinosaurs, when animals first were evolving, thinking about tomorrow was distinctly less important than finding good grub today (not much has changed on this score). These primitive animals had another concern -- trying not to wind up inside something with sharper teeth. Both factors explain why the first nerves to develop were in the digestive tract.
When animals began doing more than just eating (say choosing a good wine to complement dinner), they evolved that better-known brain in the skull. But instead of replacing the downstairs brain, the upstairs brain was hooked up to it. And it turns out that both brains originate from a structure called the neural crest, which appears and divides during fetal development to form both thinking machines.
The enteric nervous system, present in all vertebrates (defined), has these functions: to regulate the normal (digestive) activity of the digestive system and prepare it for whatever its future may hold: whether it be sampling lobster thermidor or dodging a headlong charge from the king of the tigers.
With a population of 100 million nerves, the enteric nervous system is as complex as the better studied spinal cord. And like the spinal cord, it transmits and processes messages. (Want to see our coverage of spinal cord repair? Things could be looking up for paralyzed people.)
And while this nervous system isn't protected by a skull, many of its structures and chemicals parallel those of the mainframe brain. It has sensory and motor neurons, information processing circuits, and the glial cells (defined). It uses the major neurotransmitters: dopamine, serotonin, acetylcholine, nitric oxide and norepinephrine. It even has benzodiazepines, chemicals of the family of psychoactive drugs that includes Valium and Xanax.
Please explain. Sorry. Can't. Nobody knows. But it's an indication of the complexity of the gut-brain, and of the number of questions remaining to be answered about it.
I wonder what my stomach thinks about that?
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