HISTOCHEMICAL-STUDY OF THE CANINE INFERIOR PHARYNGEAL CONSTRICTOR MUSCLE - IMPLICATIONS FOR ITS FUNCTION

The inferior pharyngeal constrictor muscle (IPC), which consists Of ti le thyropharyngeal (TP) and cricopharyngeal (CP) muscles. plays an imp ortant role during deglutition. The histochemical properties of the ca nine TPC muscle were investigated. The motor endplates OF the TP muscl e clustered at the midlength of tile muscle, while those of the CP mus cle were scattered diffusely. The glycogen depletion technique suggest ed that most of the CP muscle fibers terminated into the belly of the muscle and fiber lengths varied. With ATPase stain, type II fibers wer e shown to be predominant in the TP muscle. while type I fibers were p redominant ill the CP muscle. The diameter of the TP muscle fibers was significantly larger than that of the CP muscle. Although the histoch emical characteristics of these two muscles were markedly different, t hey gradually changed, resulting in their coordinated physiological mo vements.