AN ELECTROMYOGRAPHIC ANALYSIS OF REFLEX DEGLUTITION

Abstract

The electromyographic pattern of activity of deglutition was observed in 22 muscles in the area of mouth, pharynx, and larynx of monkey, cat, and dog. While such motor units as could be identified seemed to fire an unpredictable and random pattern from one swallow to the next, the over-all schedule of excitation and inhibition among participating muscles was highly constant. No difference in temporal pattern, duration or amplitude were found in swallows evoked by various means. A "leading complex," consisting of superior constrictor, palatopharyngeus, palatoglossus, posterior intrinsic muscles of the tongue, styloglossus, stylohyoideus, geniohyoideus, and mylohyoideus, fire concurrently for 250-500 msec to initiate the act. Other muscles, such as middle constrictor, thyrohyoideus and thyroarytenoideus, are inhibited at the onset, becoming active after varying delays. Action in the inferior constrictor is deferred until leading muscle action is nearly over. There is no great species variation save in muscles of the larynx. Sternothyroideus, sternohyoideus, intrinsic muscles of the anterior tongue and digastricus of cat and dog are silent in deglutition but participate in other synergies such as licking, chewing, and emesis. Procainization, stretch or transection of various participating muscles, cocainization of the pharynx, and administration of strychnine, anesthetics or moderate asphyxia all failed to effect substantial alteration of the pattern of deglutition. Electromyographic evidence is incompatible with a neural coordinating system requiring continued afferent regulation or collateral linkages between motor nuclei.