The Human Communicating Nerve: An Extension of the External Superior Laryngeal Nerve That Innervates the Vocal Cord

OBJECTIVE: A second source of motor innervation for the thyroarytenoid (TA) muscle, other than the recurrent laryngeal nerve, has been suggested by clinical and experimental observations. Early anatomists noted what appeared to be small nerves connecting the cricothyroid and TA muscles; however, these observations were disputed by later anatomists and subsequently forgotten. METHOD: In this study, we processed 27 human hemilarynges with Sihler's stain, a technique that clears soft tissue and counterstains nerve. In addition, four communicating nerves (CNs) were frozen sectioned and stained for acetylcholinesterase, a marker for motor neurons. RESULTS: In 12 (44%) of the 27 specimens, a neural connection was found that exited the medial surface of the cricothyroid muscle and then entered into the lateral surface of the TA muscle. In general, this CN was composed of two parts: an intramuscular branch usually combined with the recurrent laryngeal nerve or terminated within the TA muscle directly and an extramuscular branch that passed through the TA muscle and terminated in the subglottic mucosa and around the cricoarytenoid joint. All four CNs tested positive for acetylcholinesterase. Specifically, the CNs contained an average of 2510 myelinated axons, of which 785 (31%) were motor neurons. CONCLUSION: The results suggest that when the CN is present, it supplies a second source of motor innervation to the TA muscle and extensive sensory innervation to the subglottic area and cricoarytenoid joint. In addition, the CN may be the nerve of the fifth branchial arch, a structure that has never been identified (to our knowledge).