Nerve fiber analysis of the lingual branch of the glossopharyngeal nerve in human adult subjects.

Purpose: Fibers of the glossopharyngeal part of the superior constrictor muscle are connected with fibers of the transverse lingual muscle, forming a ring of muscle at the base of the tongue. This group of muscles constrict the midpharyngeal cavity during retrusive movement of the tongue. The purpose of this study is to identify the contribution of the lingual branch of the glossopharyngeal nerve to the neuro-motor control of three muscles: the glossopharyngeal part of the superior pharyngeal constrictor muscle, the palatopharyngeal and the palatoglossus muscles.

Methods: Six en bloc samples (9 sides), including the tissue from the skull base to the hyoid bone were obtained from adult human cadavers. Nerve fiber of the lingual branch of the glossopharyngeal nerve (main root of the glossopharyngeal nerve) was examined by the use of a binocular stereomicroscope.

Results: We observed that, after branching to the stylopharyngeal muscle, the lingual branch of the glossopharyngeal nerve branched to the glossopharyngeal part of the superior pharyngeal constrictor muscle, the palatopharyngeal and the palatoglossus muscles before inserting into the space between the muscle layers of the superior and middle pharyngeal constrictors.

Conclusion: These neuromuscular arrangements may suggest the presence of specialized constrictive movements of the midpharygeal cavity at the level of the base of the tongue with the retrusive movement of the tongue. The simultaneous contraction of the palatopharyngeal and palatoglossus muscles on the pharyngeal stage of deglutition may aid in the passage of bolus from the oral cavity to the midpharyngeal cavity by increasing pharyngeal pressure.