Figure 7 - Neural pathways to the LES and crural diaphragm.

Esophageal peristalsis and relaxation of the LES induced by swallow result from the excitation of receptors in the pharynx. The afferent stimulus travels to the sensory nucleus, the nucleus solitarius (small insert). A programmed set of events from the dorsal vagal nucleus and the nucleus ambiguus mediates esophageal peristalsis and sphincter relaxation. The vagal efferent fibers communicate with myenteric neurons that mediate LES relaxation (large inset). The postganglionic transmitters are nitric oxide (NO) and vasoactive intestinal peptide (VIP). Transient lower esophageal sphincter relaxation (TLESR), the principal mechanism of reflux, appears to use the same efferent neural pathway as the swallow reflex. The afferent signals for TLESR may originate in the pharynx, larynx, or the stomach. The efferent pathway is in the vagus nerve, and nitric oxide is the postganglionic neurotransmitter responsible for LES relaxation. Contraction of the crural diaphragm is controlled by the inspiratory center in the brainstem and the nucleus of the phrenic nerve. The crural diaphragm is innervated by right and left phrenic nerves through nicotinic cholinergic receptor acetylcholine (Ach). +, excitatory effects; –, inhibitory effects. (Source: Mittal and Balaban². Copyright © 1997. Massachusetts Medical Society.)