The UES participates in a number of digestive tract reflexes that either act to open the sphincter or increase UES tone.ĭata compiled from three different studies of the position of the UEHPZ with respect to individual pharyngeal muscles based on combined manometric and videofluoroscopic studies.The specific actions of individual muscles of the UES depend on the particular function, that is, tone generation, swallowing, belching, retching, or vomiting.The nucleus ambiguus is the primary motor nucleus of the UES, and the nucleus tractus solitarius is the primary termination site of UES afferents.The UES motor and sensory functions are controlled by branches of the glossopharyngeal and vagus nerves.The UES opening muscles include anteriorly the superior and inferior hyoid muscles and posteriorly the superior pharyngeal muscles.The function of intermittent UES opening is to allow transphincteric flow of fluid or gas during orthograde events, for example, swallowing, or antegrade events, for example, emesis.The UES is opened intermittently by relaxation of its sphincteric muscles, contraction of its distracting muscles, and bolus pulsion.The main functions of UES closure are to prevent esophageal air insufflation during negative intrathoracic pressure events, for example, inspiration, and to prevent esophagopharyngeal/laryngeal reflux during esophageal peristalsis.The upper esophageal sphincter ( UES) closure muscles include the cervical esophagus, cricopharyngeus, and inferior pharyngeal constrictor, but primarily the cricopharyngeus.
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