The two muscle groups that make up the upper esophageal sphincter are?

• A. Cricopharyngeal and esophageal muscles
• B. Cricopharyngeal muscle only
• C. Esophageal muscle only
• D. Pharyngeal constrictor muscles and cricopharyngeal muscle

Answer: (A)

The upper esophageal sphincter is formed by two muscular elements working together: the cricopharyngeal portion of the inferior pharyngeal constrictor and the proximal esophageal circular muscle. The cricopharyngeal part provides the upper boundary and tonic contraction to keep the opening closed at rest, while the proximal esophagus forms the lower boundary and participates in opening when a swallow is initiated. During swallowing, the cricopharyngeus relaxes and the proximal esophagus allows the bolus to pass through into the esophagus.

Choosing only the cricopharyngeal muscle misses the contribution from the proximal esophagus, and choosing only the esophageal muscle misses the upper boundary formed by the cricopharyngeus. The combination of cricopharyngeal and esophageal muscles best represents the two musculo-myogenic components that create the UES.