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Everyone is familiar with the phrase “butterflies in the stomach,” but have you ever wondered why emotions like nervousness and excitement manifest themselves as sensations in our guts?
It all has to do with the network of neurons that lines our gastrointestinal tract. This neural tissue is called the enteric nervous system and has been nicknamed the “second brain” due to its pivotal role in mental health and overall wellness.
There are an estimated 100 to 500 million neurons embedded in the walls of the GI tract (also known as the digestive tract or the alimentary canal), reaching from the esophagus to the anus. The enteric nervous system takes charge of digestion, from secreting digestive enzymes and breaking down food to absorbing nutrients and expelling waste. Although it can operate independently, the enteric nervous system normally communicates with the central nervous system via the sympathetic and parasympathetic nervous systems.
The enteric nervous system also has a surprisingly large impact on our emotions and state of mind. Researchers have found that the vast majority of fibers in the vagus nerve transmit information from gut to brain rather than from brain to gut. In addition to the classic "butterflies in the stomach,” which is a physiological stress response, the enteric nervous system can also communicate with the brain to promote emotional well-being.
The precise importance of the so-called "gut-brain axis" (two-way biochemical signaling between the GI tract and the central nervous system) is only beginning to be understood. However, the microbiome (the numerous microorganisms that inhabit the digestive tract) also appears to have a pivotal role in brain development, stress, anxiety, and memory. A promising field of research involves learning about the neuroactive compounds produced by gut microbiota and measuring the effects of probiotics not only on the gut but also on mental health.
The second brain in your guts:
- Interestingly, around 90% of the body’s entire serotonin content and 50% of its dopamine content are located in the gut. Thus, when someone takes a selective serotonin reuptake inhibitor (SSRI) as an antidepressant, the increase in serotonin can lead to gastrointestinal issues.
- Research indicates that GI issues such as irritable bowel syndrome may trigger mood swings in the central nervous system (CNS). Anxiety and depression may contribute to IBS and functional bowel problems, as well as the other way around.
- While the enteric nervous system contains many important neurotransmitters, it is still vastly different from our actual brain, which is unique in having consciousness and making decisions.