[Auxiliary motor innervation of the laryngeal muscles via the internal branch of the superior laryngeal nerve]

Abstract

According to our present knowledge of the neuromuscular innervation of the intrinsic laryngeal muscles, the cricothyroid muscle is innervated by the external branch of the superior laryngeal nerve (NLS), whereas all other remaining muscles get their supply from the inferior laryngeal (recurrent) nerve. Mainly in the phoniatric literature, however, opinions differ concerning an additional motoric laryngeal innervation. In human larynges, excised for large unilateral carcinoma, horseradish peroxidase (HRP) was injected into the internal branch of the NLS. Anterograde labelling of axons was demonstrated histochemically. In adjacent sections of the different muscles, end plates and axons were stained histochemically with silver impregnation and acetylcholinesterase. Evidence is presented of motor innervation of the internal branch of the NLS in some laryngeal muscles. With retrograde HRP-tracing in sheep, motoneurons were detected in the nucleus ambiguus, although the recurrent nerve and the external branch had been divided and excised. Thus, histologically an additional neuromuscular supply via the internal branch of the NLS is demonstrated.