The digestive tract is unique among internal organs because it is exposed to a large variety of physiochemical stimuli from the external world in the form of ingested food. As a consequence, the intestine has developed a rich store of co ordinated movements of its muscular apparatus along with neural apparatus to ensure the appropriate mixing and propulsion of contents during digestion, absorption, and excretion.

The neural apparatus of our digestive tract comprises of such a vast and complicated network of neurons that it has been nicknamed by scientists as the second brain!

Research in this area 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. Scientists are also working to find out how trillions of bacteria in the gut 'communicate' with the cells of gut nervous system.

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 of hunger. The little brain in our inner yards, in connection with the big one in our skull, partly determines our mental state and plays key roles in certain diseases throughout the body.

Often you may have experienced that if you have tension for some reason you start having loose motions. What does this show us?

Although its influence is far-reaching, the second brain is not the seat of any conscious thoughts or decision-making. 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 oesophagus to the anus. The second brain contains some 100 million neurons, more than in either the spinal cord or the peripheral nervous system. This multitude of neurons in the enteric nervous system enables us to "feel" the inner world of our gut and its contents. Stimulating and coordinating the breaking down of food, absorbing nutrients, and expelling of waste requires chemical processing, mechanical mixing and rhythmic muscle contractions that move everything down the line.

Thus equipped with its own reflexes and senses, the second brain can control several gut functions often independently of the brain. Several scientists also believe that the system is a way too complicated to have evolved only to make sure things move through and out of our gut smoothly.