Gut-Brain Connection

23 Jul

Have you ever had a “gut-wrenching” experience? Do certain situations “make you nauseous”? We use these expressions to describe emotional reactions because emotions often trigger symptoms in the gastrointestinal tract. Nerves, stresses, mental problems, and other psychological factors can wreak havoc in the gut (see Your Gut Reactions). That’s because the brain and the gastrointestinal system are intimately connected.

The entire journey of food through the 30-foot-long digestive tract is quarterbacked by a remarkable communication network known as the enteric nervous system (ENS). This intricate nerve complex is located in the gut wall and communicates with the brain via the spinal cord. In turn, hormones, neuro­transmitters, and connections to the central nervous system that affect muscles, mucosa, and blood vessels in the digestive tract influence the ENS.

The ENS cells in the lining of the gut communicate with the brain, first via the sympathetic nerves that pass to and from the gut through transformers called sympathetic ganglia. These nerves connect to the spinal cord and then to the base of the brain. In addition, parasympathetic nerves link to 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 chemicals called neurotransmitters to send electrochemical messages to one another by way of these nerves. Scientists say that this sophisticated “gut-brain” system is nearly equal in size and complexity to the body’s central nervous system.

Imaging studies of the brain show that functional GI symptoms are not necessarily the result of dysfunction in the bowel, but may be due to disturbances in brain-gut pathways that lower pain thresholds, affect movement through and contractions of the GI tract, and alter behavior.

We know that the brain has a direct effect on the stomach if only because the thought of eating can set off the stomach’s appetite juices even before food gets there. But the action goes both ways. A troubled intestine can send signals to the brain just as a troubled brain can send signals to the gut. A patient’s distressed gut might, therefore, be as much the cause as the product of depression or anxiety. 

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