Dr. Michael D. Gershon's book, “The Second Brain”, caught my attention with its cover ad: “Your gut has a mind of its own.” I thought it would tell me how the unconscious mind interacts with the body to give us gut feelings. It's actually about the enteric nervous system, which runs the digestive system. It is often considered to be part of the autonomic nervous system, but Gershon describes it as complicated and independent enough to deserve the designation of second brain.
Peristalsis is the name for the way food moves through the intestines. It requires a great deal of coordination of the smooth muscles that squeeze food along the long tube, to keep everything moving in the right direction. The enteric nervous system is in charge of synchronizing these contractions. When something disturbs the nerve signals, such as antidepressant drugs that change neurotransmitter concentrations, then we get symptoms such as nausea, cramps, and constipation or diarrhea (possibly alternating).
A similar process happens in inflammatory bowel disease (IBD). This condition affects approximately 3.6 million people in the United States and Europe, and is on the rise in other parts of the world where it was previously less common. Researchers state in Reference 2 that more information is needed about the cause and mechanisms of the disease in order to produce lasting, effective treatments.
Most attention has been focused on inflammation of the intestinal walls. However, data from patients and from animal models demonstrates that inflammation can also damage the enteric nerves. The damage is sometimes visible as changes in the structure of these nerves. Other changes occur at the level of neurotransmitters. These alterations can affect the function of the enteric nervous system's regulation of all aspects of intestinal function, including:
1. Gut motility
2. Transport of fluid and electrolytes
3. Secretion of mucins
4. Production of cytokines
5. Regulation of epithelial barrier function
Thus, even when inflammation of the intestinal walls appears to be in remission, IBD patients can still have significant symptoms if inflammation persists in the enteric nerves.