Enteric Nervous System
Neuroanatomists recognize another subdivision of the nervous system, the enteric nervous sytem. This is the network of motor and sensory neurons embedded in the walls of the gastrointestinal tract and its accessory glands (e.g., pancreas, liver).
Activity in the enteric nervous system is influenced by the parasympathetic and sympathetic divisions of the ANS, but the system is functional without input from outside the viscera. Two dense networks of neurons are found in the walls of these organs. one, the submucosal (Meissner’s) plexus, is just deep to the inner lining of the gut. The other, the myenteric (Auerbach’s) plexus, is found within the muscular layer.Normally the motor output of the ANS controls the overall activity of the viscera, but in large part the intrinsic neurons of the enteric nervous system control local events. Sensory neurons monitor local stretch, chemical composition of the gut’s contents, and gastrointestinal hormones. Activity in these sensory neurons stimulates local reflex movements, mediated by the motor neurons of the enteric nervous system. In this way, motility of the gut, dilation of local blood vessels, and secretions can be adjusted to meet the immediate local demands of digestion.