AXONS ENTER THE HUMAN POSTERIOR CRICOARYTENOID MUSCLE FROM THE SUPERIOR DIRECTION

Objective: To examine the possibility that axons from the superior lar yngeal nerve travel inferiorly through connections between the recurre nt and the superior laryngeal nerves within the interarytenoid muscle to innervate intrinsic laryngeal muscles. Materials: The branch point from the recurrent laryngeal nerve to the posterior cricoarytenoid mus cle was excised from five human larynges. Methods: The section of nerv e was first microdissected to remove the epineurium. Then, the specime n was incubated at 37 degrees C in a 1% collagenase solution, which wa s alternated with 0.4% chymopapain or 0.25% trypsin. Finally, the spec imen was stained with 1% toluidine blue. Results: In all five specimen s, axons could be seen entering the nerve branch to the posterior cric oarytenoid muscle from the superior direction. In one specimen, about one third of the axons entering the muscle could be identified as aris ing from the superior direction. In two cases, the superior axons coul d be traced back to the recurrent laryngeal nerve branch to the intera rytenoid muscle. Conclusions: These results suggest that axons from th e superior laryngeal nerve connect with the recurrent laryngeal nerve in the area of the interarytenoid muscle. Furthermore, these a?tons tr avel inferiorly to innervate the posterior cricoarytenoid muscle.