Scanning electron microscopic study of the muscle fiber arrangement in the rat cricopharyngeal muscle.

Conclusions: Myomyous junctions comprise a complex muscle fiber network, which is thought to synchronize the activity of the cricopharyngeal (CP) muscle fibers. Myomyous and myotendinous junctions explain the heterogeneity in muscle fiber length which contributes to the efficient behavior of the muscle. This scanning electron microscopy (SEM) study demonstrated the complex muscle fiber arrangement of the CP muscle and improved on the previous description of its morphological specificity.
Objective: To examine the 3D ultrastructure of the inferior pharyngeal constrictor muscle fibers to obtain further knowledge of their morphological characteristics with regard to the specific functions of the muscle in deglutition.
Material and Methods: Six adult rats were used. Their CP and thyropharyngeal (TP) muscles were obtained and processed using the HCl hydrolysis method to remove i.m. connective tissue. The fine muscle fiber structure was observed by means of SEM.
Results: Multifaceted muscle fiber interconnections (myomyous junctions) were identified in the CP muscle. The myomyous junctions were characterized by the tight connection of many finger-like processes at the ends of a lateral branch or bifurcating trunk of the muscle fibers. In addition, muscle fibers occasionally tapered and ended within the muscle belly, forming myotendinous junctions. The TP muscle lacked these structures.