You actually have two nervous systems
Central nervous system, composed of your brain and spinal cord
Enteric nervous system, which is the intrinsic nervous system of your gastrointestinal tract
Both are created from identical tissue during fetal development—one part turns into your central nervous system while the other develops into your enteric nervous system. These two systems are connected via the vagus nerve, the tenth cranial nerve that runs from your brain stem down to your abdomen. It is now well established that the vagus nerve is the primary route your gut bacteria use to transmit information to your brain.
While many think of their brain as the organ in charge, your gut actually sends far more information to your brain than your brain sends to your gut… To put this into more concrete terms, you’ve probably experienced the visceral sensation of butterflies in your stomach when you’re nervous, or had an upset stomach when you were very angry or stressed. The flip side is also true, in that problems in your gut can directly impact your mental health, leading to issues like anxiety and depression.
Just as you have neurons in your brain, you also have neurons in your gut — including neurons that produce neurotransmitters like serotonin, which is also found in your brain. In fact, the greatest concentration of serotonin, which is involved in mood control, depression and aggression, is found in your intestines, not your brain. It’s quite possible that this might be one reason why antidepressants, which raise serotonin levels in your brain, are often ineffective in treating depression, whereas proper dietary changes often help.
Your Gut Microbes Can Affect Your Health in Numerous Ways
In recent years, it’s become increasingly clear that the microbes in your gut play a much more vital role in your health than previously thought possible. In fact, probiotics, along with a host of other gut microorganisms, are so crucial to your health that researchers have compared them to “a newly recognized organ.” Besides research implicating gut bacteria in mental health and behavior, other research has shown that your microbiota also has an impact on immune system function, gene expression, sugar regulation, and weight management.