Axons Enter the Human Posterior Cricoarytenoid Muscle From the Superior Direction

Objective: To examine the possibility that axons from the superior laryngeal nerve travel inferiorly through connections between the recurrent 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 muscle was excised from five human larynges. Methods: The section of nerve was first microdissected to remove the epineurium. Then, the specimen was incubated at 37°C in a 1% collagenase solution, which was alternated with 0.4% chymopapain or 0.25% trypsin. Finally, the specimen was stained with 1% toluidine blue. Results: In all five specimens, axons could be seen entering the nerve branch to the posterior cricoarytenoid muscle from the superior direction. In one specimen, about one third of the axons entering the muscle could be identified as arising from the superior direction. In two cases, the superior axons could be traced back to the recurrent laryngeal nerve branch to the interarytenoid muscle. Conclusions: These results suggest that axons from the superior laryngeal nerve connect with the recurrent laryngeal nerve in the area of the interarytenoid muscle. Furthermore, these axons travel inferiorly to innervate the posterior cricoarytenoid muscle.