![]() ![]() ![]() Muscle fibers of the cricopharyngeus have both slow (oxidative) and fast (glycolytic) type fibers, even though slow ones predominate. Fibers of thyropharyngeus are placed obliquely (pars obliques) and cricopharyngeus horizontally (pars profundus) to form the UES ( Figure 7). Accordingly, a surgical incision of 5–6 in length, which extends over inferior pharyngeal constrictor, cricopharyngeus, and cervical esophageal muscle, is required to completely ablate the UES pressure (as measured by the Sleeve sensor in the humans ). Furthermore, cricopharyngeus is only 1 cm in width but the UES pressure zone is 3–4 cm long. Simultaneously, pressure and fluoroscopic imaging studies show that the peak pressure of the UES high-pressure zone is located above the cricopharyngeus muscle ( Figure 6). Even though it is generally agreed that cricopharyngeus is a major contributor to the UES high-pressure zone, thyropharyngeus (part of inferior pharyngeal constrictor) and cervical esophagus also contribute to it in its proximal and distal extents, respectively. Anatomically, it is located behind the cricoid cartilage but extends both above and below it. It is best recognized functionally as a high-pressure zone that extends 3–4 cm in its vertical extent. It has two major functions: (1) to prevent air from entering into the esophagus during breathing and (2) to prevent reflux of esophageal contents into the pharynx to guard airway aspiration. Upper esophageal sphincter (UES) has also been referred to as the inferior pharyngeal sphincter because it is located at the lower end of pharynx and guards the entrance into the esophagus. ![]()
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