Your body contains a separate nervous system which is so complex, it has been called the second brain.  It comprises an estimated 500 million neurons (nerve cells), and is around 9 metres long, stretching from your esophagus to your anus.  Embedded in the wall of your gastro-intestinal system (GIT), the enteric nervous system (ENS) has long been known to control digestion.  However, more and more research illustrates the profound role the ENS plays in our physical and mental well-being.  It can work independently or in conjunction with our brain in our head (first brain).  The ENS helps the body sense environmental threats, and there is a lot of communication back and forth between the second and first brain.

Besides the dedicated role of the ENS in overseeing all aspects of digestion, the process of eating is also fraught with danger.  Like the skin, the GIT must stop potentially dangerous viruses and bacteria from gaining access into the body.  Should this happen, immune cells in the gut wall will secrete chemicals , which will be detected by the nerve cells (neurons) of the ENS. This triggers the second brain to respond with diarrhea, or alerts the first brain in our head, which may respond with vomiting, or both reactions may occur.

The first and second brain share many common features. Both are made up of many different type of neurons, with glial support cells.  The ENS has its own version of the blood brain barrier to maintain a stable physiological environment in order to function.  It produces a wide range of hormones and about 40 neurotransmitters, identical to those produced in the human brain. Interestingly at any moment, 95% of the serotonin present in the body at any time is in the ENS.  In the human brain, dopamine is a signaling molecule associated with pleasure and the reward system – however, in the gut (second brain) it also transmits messages between neurons that co-ordinate muscle contractions.  Serotonin, the “feel-good” neurotransmitter in our brain is involved in preventing depression; regulating sleep, appetite and body temperature, whereas serotonin released in the gut ENS, via transport in the blood stream, is involved in physiology of the liver and the lungs.  Serotonin also acts as a vital growth factor for the proper development of the ENS.

There are strong links between our gut and our mental state at any moment because a lot of information about our environment comes from our gut.  As researcher Michael Gershon at the Columbia-Presbyterian Medical Centre, New York, states “Remember the inside of your gut is really the outside of your body.  So we can see danger with our eyes, hear it with our ears, and detect it in our gut”.  Hence for good health it is critical for the brain to have direct and intimate connection with the gut (second brain).

As more and more research is being done to understand the complex and amazing relationship between these 2 brains, it is becoming apparent that the gut ENS offers a window into the pathology of the human brain.




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