Abstract
The inferior pharyngeal constrictor muscle, which consists of two components; the thyropharyngeal muscle (TPM) and cricopharyngeal muscle (CPM), plays an important role during pharyngeal swallowing stage. The TPM drives the bolus into esophagus in harmony with other muscles. The CPM functions as upper esophageal sphincter at rest and relaxes at pharyngeal swallowing stage. The TPM and CPM showed markedly different characteristics each other in respects of gross anatomy, distribution of the neuromuscular junctions, muscle fiber type composition and diameter of muscle fibers. Also, the CPM was proved to be an unique muscle in comparison with other skeletal muscles. A gradual transition of the characteristics was observed between the TPM and CPM without distinct boundary. This may contribute to the coordinated physiological movement of the inferior pharyngeal constrictor muscle.
