Histochemical study of the canine inferior pharyngeal constrictor muscle: implications for its function

The inferior pharyngeal constrictor muscle (IPC), which consists of the thyropharyngeal (TP) and cricopharyngeal (CP) muscles. plays an important role during deglutition. The histochemical properties of the canine IPC muscle were investigated. The motor endplates of the TP muscle clustered at the midlength of the muscle, while those of the CP muscle were scattered diffusely. The glycogen depletion technique suggested that most of the CP muscle fibers terminated into the belly of the muscle and fiber lengths varied. With ATPase stain, type II fibers were shown to be predominant in the TP muscle, while type I fibers were predominant in the CP muscle. The diameter of the TP muscle fibers was significantly larger than that of the CP muscle. Although the histochemical characteristics of these two muscles were markedly different, they gradually changed, resulting in their coordinated physiological movements.