Anatomy and physiology of the enteric nervous system

Abstract

The enteric nervous system (ENS) is a quasi autonomous part of the nervous system and includes a number of neural circuits that control motor functions, local blood flow, mucosal transport and secretions, and modulates immune and endocrine functions. Although these functions operate in concert and are functionally interlinked, it is useful to consider the neural circuits involved in each separately.1 This short summary will concentrate mainly on the neural circuits involved in motor control.2 The enteric neural circuits are composed of enteric neurones arranged in networks of enteric ganglia connected by interganglionic strands. Most enteric neurones involved in motor functions are located in the myenteric plexus with some primary afferent neurones located in the submucous plexus. As in all nervous systems involved in sensory-motor control, the ENS comprises primary afferent neurones, sensitive to chemical and mechanical stimuli, interneurones and motorneurones that act on the different effector cells including smooth muscle, pacemaker cells, blood vessels, mucosal glands, and epithelia, and the distributed system of intestinal cells involved in immune responses and endocrine and paracrine functions. The digestive tract is unique among internal organs because it is exposed to a large variety of physicochemical stimuli from the external world in the form of ingested food. As a consequence, the intestine has developed a rich repertoire of coordinated movements of its muscular apparatus to ensure the appropriate mixing and propulsion of contents during digestion, absorption, and excretion. The oro-aboral transit of the intestinal contents can be regarded as a form of adaptive locomotion that occurs over a wide range of spatial and temporal domains.3 The movements of the intestine are the result of interaction of the neural apparatus and the muscular apparatus.4 The muscular apparatus is organised in muscle layers made up of large collections of smooth muscle cells …