Enteric nervous system

The enteric nervous system (ENS) derives from the neural crest and consists of neurons distributed in two ganglionated plexuses, myenteric and submucosal, located within the walls of the gut. The ENS contains as many neurons as the spinal cord (approximately 80-100 million neurons) and controls intestinal motility and secretion largely independently of influences from the CNS.1–5 The ENS is affected by Lewy body pathology at early stages of PD,6,7 and by many genetic8,9 or immune9,10 neurologic disorders associated with gastrointestinal dysmotility. The aim of this paper is to briefly review the functional and neurochemical organization of the ENS and its involvement in neurologic disorders. There are recent comprehensive reviews on these subjects.3,8,9,11,12 The control of motility and secretion in the gastrointestinal tract depends on both extrinsic parasympathetic and sympathetic innervation and intrinsic innervation, provided by the ENS. Extrinsic parasympathetic inputs originate in the dorsal motor nucleus of the vagus, which controls primarily the motility of the esophagus and stomach, and the sacral parasympathetic nucleus, which contributes to control of motility of the distal colon and rectum. The prevertebral sympathetic ganglia mediate peripheral reflexes that inhibit motility of the gut. The intrinsic innervation of the gut consists of the ganglia of the ENS, which are grouped into two plexuses: the myenteric plexus (of Auerbach), located between the outer longitudinal and the inner circular muscle layers, and submucosal plexus (of Meissner), located between the circular muscle and the muscularis mucosae (figure).1–4 The ENS controls intestinal motility and secretion largely independently of extrinsic parasympathetic and sympathetic innervation, although these extrinsic influences have a modulatory role on ENS activity. Neurons of the myenteric plexus control the activity of the smooth muscle of the gut whereas those in the submucosal plexus also regulate mucosal secretion and blood flow. …