The upper esophageal sphincter (UES) (also called the Pharyngoesophageal sphincter) refers to the superior portion of the esophagus. Unlike the lower esophageal sphincter, it consists of striated muscle and is under conscious control. The primary muscle of the UES is the cricopharyngeus portion of the inferior pharyngeal constrictor. During swallowing the upper esophageal sphincter opens so the bolus can pass into the esophagus. A secondary role of the UES is to reduce backflow from the esophagus into the pharynx. [ http://en.wikipedia.org/wiki/Upper_esophageal_sphincter ]