How do the brain and digestive system work together?

Lawrence S. Friedman, MD
It is helpful to understand the similarities and connections between the brain and the digestive system. The gut is controlled by the enteric nervous system (ENS), a complex system of about 100 million nerves that oversees every aspect of digestion. The ENS is heavily influenced by the central nervous system (CNS), with which it communicates through pathways of nerves. The "second brain," as the ENS is sometimes called, arises from the same tissues as the CNS during fetal development. It has many structural and chemical counterparts in the cranial brain, including sensory and motor neurons as well as glial cells, which support and protect the neurons. And the ENS uses many of the same neurotransmitters, or chemical messengers, as the CNS.

The ENS is embedded in the gut wall and participates in a rich dialogue with the brain during the entire journey of food through the 30-foot-long digestive tract. The ENS cells in the lining of the gut communicate with the brain by way of the autonomic nervous system, which controls the body's vital functions. As part of that system, sympathetic nerves connect the gut to the spinal cord and then to the base of the brain. In addition, parasympathetic nerves pass to and from the base of the brain via the vagus nerve from the upper gut or the sacral nerves from the colon. The gut and brain use their shared neurotransmitters, including acetylcholine and serotonin, to transmit information back and forth by way of the sympathetic and parasympathetic nerves.

This two-way communication system between the gut and the brain explains why you stop eating when you're full (sensory neurons in your gut let your brain know that your stomach is distended), or conversely, why anxiety over this morning's exam has ruined your appetite for breakfast (the stress activated your "fight or flight" sympathetic nervous system, inhibiting gastrointestinal secretion and reducing blood flow to the gut).

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.