The human cognitive system mainly constitutes the brain, and partly the spinal cord. However, besides these two organs, our bodies also have the third kind of nervous system called the "enteric nervous system" or sometimes the "second brain" . Generally, more than 100 million neuro-muscular synapses lined this double-layered system, starting from the oesophagus till rectum . It is thought that the brain and gut are linked, might be with some mysterious bonds, and maybe that's why sometimes only thinking about our favourite food leads to its craving and secretion of digestive enzymes in the gut .
What does science say about all this phenomenon?
Until recently, scientists thought that the enteric system and brain only communicate through hormones produced by enteroendocrine cells of the gut lining . But, a new study demonstrated that after sensing some kind of nutrient or microbe, the enteroendocrine cells also trigger the release of some kind of molecular messengers which modulates the nervous system and eventually the behaviours of the host . Moreover, these cells also have microvilli, tiny protrusions towards the gut, neuropods, and some other kind of physical attributes similar to that of neurons . This also emphasizes their direct wiring with the neurons and interference in brain functioning.
Unfortunately, all these findings are superficial and their exact mechanisms are still not known. For example, it is still in oblivion that how a chemical signal from a food nutrient or microbe gets transformed into an electrical signal that ultimately alters behaviours. Understanding the relationship between gut and brain has immense medical significance, as describing the communication pathways between these two, someday could lead us to discoveries of treatments for various ailments like; autism, obesity, anorexia, irritable bowel syndrome, inflammatory bowel disease, PTSD and chronic stress etc.