![]() ![]() ![]() Nerve cell bodies of the vagal efferent fibers are located in the nucleus ambiguus. All these nerves form a pharyngeal plexus before penetrating into the muscle fibers. The vagus nerve, through its pharyngeal, superior laryngeal and recurrent laryngeal nerve branches, is the major motor nerve of the UES. UES is innervated by the glossopharyngeal, branches of vagus, ansa cervicalis, and sympathetic nerves (from cervical ganglion). Although hyoid bone movement during swallowing was invariably upward, forward, and counterclockwise, its movement during belching was mainly anterior (more.) Open circles indicate UES opening observed by videofluoroscopy. Trajectory of UES with swallow and belch. Muscle spindles are absent from the UES muscle but Golgi-tendon-like structure, through which motor neurons may monitor muscle tone, is present. As a result, the greater the diameter of the manometry probe the greater the measured UES pressure. However, the in vivo operational length of the UES muscle is significantly shorter than its optimal length (1.7 times). Most skeletal muscles generate maximal force at what is referred to as the optimal muscle length. Cricopharyngeus originates from the cricoid cartilage, loops around the pharynx in a C or “horse shoe shape manner,” and is inserted back into the cricoid cartilage (unique muscle that has origin and insertion into the same structure). Forty percent of the muscle mass is contributed by the collagen and elastic tissue (endomysial tissue), and it is felt that the UES is functionally quite compliant even though noncompliant cricoid cartilage forms its anterior extent. Slow fibers most likely contribute to the tonic and fast fibers to the phasic contractions that are involved in rapid reflex contractions of the UES high-pressure zone. 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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