Chapter 5 - The Enteric Nervous System

Summary

The enteric nervous system (ENS) is an autonomic nervous system in its own right. It can function independently of the central nervous system. The neurons of the ENS are located the ganglia of the myenteric or submucosal plexus and consist of intrinsic primary afferent neurons, interneurons and motor neurons innervating various effectors. The primary transmitter in most excitatory enteric neurons is acetylcholine. Inhibitory motor neurons use several cotransmitters. Afferent neurons, interneurons and motor neurons form reflex circuits that underlie the neural regulation of motility, secretion, reabsorption, local blood flow and in protective reactions of the gastrointestinal tract. Motility patterns are mainly directed by the myenteric plexus. The neural basis of peristalsis consists of the coordinated activation of ascending and descending reflex pathways. The circular muscles are additionally influenced by a descending inhibitory reflex pathways. Inhibitory and excitatory reflex circuits are organized and coordinated with pacemaker activity of the interstitial cells of Cajal (ICCs) to generate the different movement patterns. The networks of ICCs are also responsible for oral-aboral contraction. Neural regulation of fluid and electrolyte transport is controlled through the submucosal plexus. The brain modulates the functions of the ENS via the parasympathetic and sympathetic nervous systems.