Final answer:
The cricopharyngeus muscle is part of the upper esophageal sphincter, which plays a vital role in the initiation of the esophageal phase of swallowing.
Step-by-step explanation:
The cricopharyngeus muscle is not an independent muscle. Rather, it is part of the upper esophageal sphincter. This muscular structure plays a critical role in swallowing or deglutition, specifically at the start of the esophageal phase.
During swallowing, the cricopharyngeus muscle relaxes to allow the passage of the food bolus from the pharynx into the esophagus. The upper esophageal sphincter then contracts to prevent the backflow of food.
The esophageal phase also involves contraction of the pharyngeal constrictor muscles and the longitudinal muscle layers of the muscularis which propel the bolus toward the stomach, assisted by peristalsis.
The cricopharyngeus, being part of the upper esophageal sphincter, is thus integral in the coordination and sequence of movements that comprise the swallowing process.