Enteric nervous system

The enteric nervous system is unique in that it can mediate reflex activity in the absence of input from the brain or spinal cord. This activity is made possible by the presence within the wall of the gut of many different types of neurons, an abundance of interneurons, and intrinsic sensory neurons. Recent advances have enabled enteric microcircuits to be investigated. Studies that have followed expression of the protooncogene, c-fos, have now established that some primary afferent neurons (which are cholinergic and costore calbindin and substance P) are submucosal. These cells are excited by deformation of the mucosa and project both to other submucosal ganglia and to the myenteric plexus. They may be activated by serotonin released from enterochromaffin cells. One type of myenteric neuron, 2/AH, has also been postulated to be a primary afferent, although some believe it is an interneuron. The 2/AH cells project widely within the myenteric plexus and to the mucosa. Although the behaviors regulated by the enteric nervous system cannot yet be explained in terms of the activity of single cells, it should soon be possible to do so.