Functional Anatomy of the Human Intrinsic Laryngeal Muscles

Abstract

BACKGROUND: Since the beginning of the Christian era, numerous reports have dealt with the construction and functional organization of the larynx, thus stressing its role as the keystone of vocalization in vertebrates. The purpose of this review is to provide a comprehensive summary of basic anatomical facts and to point out certain new aspects of the innervation of laryngeal muscles. METHODS: The data presented herein were collected from a preliminary gross anatomical study performed in six human individuals at our institute, and from published literature. RESULTS: The basic framework of the human larynx is composed of the hyaline thyroid, cricoid and arytenoid cartilages, the fibroelastic epiglottis and the hyoid bone. Two pairs of synovial articulations, i.e. the cricothyroid and cricoarytenoid joints, provide the mobility needed to adjust the tension of the vocal ligaments. The intrinsic laryngeal muscles may be divided into three functional groups: (i) muscles varying the rima glottidis (the transverse arytenoid as well as the lateral and posterior cricoarytenoid muscles); (ii) muscles regulating tension in the vocal ligaments (i.e. the cricothyroid, posterior cricoarytenoid as well as the compound thyroarytenoid and vocalis muscles) and (iii) muscles modifying the laryngeal inlet (the so-called ‘sphincter aditus’, which is formed by the oblique arytenoid and aryepiglottic muscles and counteracted by the thyroepiglottic muscle). They are innervated by the superior and inferior laryngeal nerves branching off the vagus nerve. The external branch of the superior laryngeal nerve exclusively supplies the cricothyroid muscle. There is strong evidence that the lateral cricoarytenoid and the thyroarytenoid muscles are solely supplied by the inferior laryngeal nerve. All other intrinsic laryngeal muscles seem to receive motor fibres either from both laryngeal nerves or from the internal branch of the superior laryngeal nerve alone. CONCLUSIONS: Thus, the traditional concept of motor innervation of the larynx seems to be out of date. In fact, the internal branch of the superior laryngeal nerve should no longer be seen as purely sensory but rather – as also the inferior laryngeal nerve – as a mixed nerve containing sensory as well as motor fibres.