Enteric nervous system

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Ens embedded in intestinal lining

The enteric nervous system (ENS) is an interdependent part of the autonomic nervous system. Despite its many interactions with other parts of the ANS, it can be regarded as a nerval body of its own. Its functioning is still subject to research in neurogastroenterology. It has as many as 1 billion neurons, one hundredth of the number of neurons in the brain.

The ENS is comprised of two layers:

• One is the myenteric plexus that lies between the layers of circular and longitudinal muscle lining the gut wall.
• The second is the submucosal plexus that is found between the layer of circular muscle and the submucosa.

There are several reasons why the enteric nervous system may be regarded as a second brain. The enteric nervous system can operate autonomously. It normally communicates with the CNS through the vagus nerve. However, vertebrate studies show that when the vagus nerve is severed, the enteric nervous system continues to function.

The complexity of the enteric nervous system is another reason for its status as a second brain. In vertebrates the enteric nervous system includes efferent neurons, afferent neurons, sensory neurons, motor neurons and interneurons. The sensory neurons report on mechanical and chemical conditions. Through intestinal muscles, the motor neurons control peristalsis and churning of intestinal contents. Other neurons control the secretion of enzymes. The enteric nervous system also makes use of the same neurotransmitters as the CNS, suck as acetylcholine, dopamine and seratonin. The enteric nervous system has the capacity to alter its response depending on such factors as bulk and nutrient composition.

A third reason is that during development the ENS derives from the same neural crest as the CNS.

Sources

• The book The Second Brain by Dr. Michael D. Gershon
• New York Times The Other Brain Also Deals With Many Woes "The role of the enteric nervous system is to manage every aspect of digestion, from the esophagus to the stomach, small intestine and colon. The second brain, or little brain, accomplishes all that with the same tools as the big brain, a sophisticated nearly self-contained network of neural circuitry, neurotransmitters and proteins."