What occurs to the upper esophageal sphincter (UES) after food is swallowed?

After food is swallowed, the upper esophageal sphincter (UES) relaxes to allow food to pass from the pharynx into the esophagus. This relaxation is a critical reflex that enables the bolus of food to move downward during the swallowing process. The UES is composed of striated muscle and is under voluntary control; it normally remains tightly closed to prevent the backflow of food and to protect the airway. However, upon swallowing, a complex interplay of neural signals prompts the sphincter to open, facilitating the passage of the food bolus.

Understanding this mechanism is essential because it illustrates how the UES functions in coordination with other components of the swallowing process, ensuring effective movement of food. After the food enters the esophagus, the sphincter will then return to its resting state, contracting again to prevent any regurgitation.