Role of the pharyngeal branch of the vagus nerve in laryngeal elevation and UES pressure during swallowing in rabbits.

Elevation of the larynx during swallowing plays an important role in protecting the laryngeal inlet and in the opening of the upper esophageal sphincter (UES). The thyrohyoid (TH) muscle is the most important muscle for laryngeal elevation, and it is thought to be innervated by the thyrohyoid branch. However, in preliminary studies we found that laryngeal elevation was severely disturbed after sectioning of the pharyngeal branch of the vagus nerve (X-ph). In the present study, we examined the role of the X-ph in laryngeal elevation and the contribution of this nerve to UES pressure. Ten male rabbits under anesthesia were used. Sectioning of the X-ph not only abolished the electromyographic activities of the TH and cricopharyngeus (CP) muscles, it also greatly reduced the maximal value of laryngeal elevation during swallowing. On the other hand, sectioning of the hypoglossal nerve, which contains the thyrohyoid branch, produced no appreciable change in the electromyographic activity of either muscle and it reduced the maximal value of the elevation only slightly. These results indicate that the X-ph innervates the TH and CP muscles and suggest that the X-ph plays an important role in elevating the larynx and in regulating the UES pressure in rabbits.