Cross-Innervation of the Thyroarytenoid Muscle by a Branch from the External Division of the Superior Laryngeal Nerve

Abstract

The neuroanatomy of the larynx was explored in seven dogs to assess whether there is motor innervation to the thyroarytenoid (TA) muscle from the external division of the superior laryngeal nerve (ExSLN). In 3 animals, such innervation was identified. Electrical stimulation of microelectrodes applied to the ExSLN resulted in contraction of the TA muscle, indicating that this nerve is motor in function. This was confirmed by electromyographic recordings from the TA muscle. Videolaryngostroboscopy revealed improvement in vocal fold vibration following stimulation of the ExSLN compared to without it. Previously, the TA muscle was thought to be innervated solely by the recurrent laryngeal nerve. This additional pathway from the ExSLN to the TA muscle may have important clinical implications in the treatment of neurologic laryngeal disorders such as adductor spasmodic dysphonia.

Collateral reinnervation by the superior laryngeal nerve after recurrent laryngeal nerve injury

“…Those studies have shown that branches from the SLN seem to innervate both the thyroarytenoid (TA) and the posterior cricoarytenoid (PCA) muscles. 23,24,33,41 It is also known that injection of horseradish peroxidase into the internal branch of the SLN in resected human larynges results in anterogradely labeled axons not only in the CT, but also in the TA and PCA muscles, 42 bringing the classical neuroanatomical picture further into question. The reportedly small motor unit sizes of the laryngeal muscles 10,32 reflect the requirement for precise innervation.…”

The Pharyngeal Plexus–Mediated Glottic Closure Response and Associated Neural Connections of the Plexus

“…Interestingly, stimulation of the distal branch of the eSLN in this animal led to TA muscle contraction even after subsequent RLN transection, indicating a direct pattern of innervation from the PP through the eSLN directly to the TA muscle bypassing the RLN, as shown in Figure 4. This finding was not totally unexpected, since Nasri et al 11 showed the crossinnervation of the TA muscle by the eSLN in the canine model. The second group contained 2 experimental necks that showed a short latency response to TA muscle contraction that occurred during stimulation of the central branch of the PP.…”

Injury of the external branch of the superior laryngeal nerve in thyroid surgery

“…By counterstaining neural tissue with Sihler's stain, Wu et al (15) dissected 27 human larynges and found a connection between the distal EBSLN and the recurrent laryngeal nerve (RLN) in 44% of cases, with either an intramuscular branch entering the thyroarytenoid muscle (TAM) or an anastomosis with the RLN just prior to its entrance into the TAM. Similarly, Nasri et al (16) reported in a canine model the presence of crossinnervation to the TAM in 3 of 7 dogs, with the bulk of the activity concentrated in the anterior third of the vocal cords. The microdissection study of 90 human larynges by Sañudo et al (17) found that a branch of the EBSLN continued to join the ventral branch of the RLN in 68% of the cadavers, as Maranillo et al (18) found a submucosal neural connection between the EBSLN and the RLN in the paraglottic space in 85% of 103 human larynges under ×4 to ×6 magnification.…”