2004 Volume 55 Issue 6 Pages 439-445
The cricopharyngeal muscle (CPM), the lower component of the inferior pharyngeal muscle, functions as an upper esophageal sphincter and has an important role during deglutition. Besides its multifaceted functions, specific anatomical characteristics of the CPM have been reported. In the present study, we demonstrated the fine structure of CPM fibers by scanning electron microscopy and implicated them in specific and complex behavior of the CPM. The muscle fibers occasionally branched making tight myomyous junctions between neighboring fibers. The myomyous junctions built up a muscle fiber network, which is thought to synchronize the activity of the CPM fibers. Some muscle fibers abruptly terminated in the muscle belly, exhibiting myotendinous junctions at the ends of the fibers. The myomyous and myotendinous junctions explain the heterogeneity of muscle fiber length that contributes to the efficient closure of the esophageal entrance. The CPM predominantly had a depression type of primary synaptic clefts, which seemed to be related with its physiological and evolutional characteristics. Prematured thin muscle fibers with a shallow depression type of primary synaptic cleft were occasionally identified. These findings indicated relatively frequent muscle fiber regeneration and a possible close association with the maintenance of CPM function.
