[Neural control of deglutition and esophageal motility in mammals]

Swallowing is a complex motor sequence involving the coordinated contraction of many muscles of the buccopharyngeal cavity, the larynx and the oesophagus. Most of the muscles are striated except those of the distal oesophagus which, in human and some other species, are of the smooth type. During swallowing, usually divided into a buccopharyngeal and an oesophageal stage (peristalsis), the sequential activity of the muscles results from motor orders programmed by a rhombencephalic swallowing centre and conveyed to the periphery by efferent fibres belonging to various pairs of cranial nerves (Vth, VIIth, IXth, Xth). Apart from the motor nuclei of the cranial nerves, the swallowing centre contains an nuclei of the cranial nerves, the swallowing centre contains an interneurone network responsible for the programming of deglutition. During swallowing, these interneurones (INs) exhibit a sequential activity quite parallel to that of muscles, and persisting in the absence of sensory feedback. The "swallowing INs" are located in two medullary regions: a dorsal region including the nucleus of the solitary tract and the adjacent reticular formation, a ventral region corresponding to the reticular formation surrounding the nucleus ambigus. The dorsal INs are involved in the initiation and the programming of swallowing. The ventral INs receive their swallowing input from the dorsal neurones and are probably switching neurones that distribute the swallowing excitation to the various pools of motoneurones. The swallowing program can be triggered by inputs originating from either the peripheral reflexogenic areas or the supramedullary structures (cerebral cortex in particular). Under physiological circumstances, the swallowing program is continuously modified by peripheral afferents (especially muscular) that adjust the force and the timing of contractions to the size of the swallowed bolus. In addition, an important operating feature of the programming network consists of a functional polarization so that the activity of proximal portions of the swallowing tract inhibits that of distal portions. This polarization implies the existence of inhibitory connections between interneurones, that could constitute "time-lag lines" responsible for the series of delays typical of the swallowing contractile sequence. Lastly, although the smooth muscle oesophagus contains its own programming system (intramural nervous system), motility of this area during deglutition also depends on the medullary program that combines with the intramural program by ways not yet elucidated.