Chapter 41: Larynx Anatomy

The larynx is a sophisticated anatomical structure that performs the vital functions of acting as an airway, a protective sphincter, and the principal organ of phonation, extending from the base of the tongue to the trachea. Its fundamental support comes from a series of nine cartilages, including the three single structures—the large thyroid cartilage, the complete-ring cricoid cartilage, and the leaf-like epiglottis—as well as paired components like the arytenoid cartilages. The thyroid, cricoid, and major parts of the arytenoid cartilages consist of hyaline cartilage and commonly undergo calcification beginning around the twenty-fifth year. Motion control relies on two sets of synovial joints: the cricothyroid joints, which facilitate rotation to lengthen and increase tension in the vocal folds, thereby elevating the pitch of the voice, and the cricoarytenoid joints, which use rocking and gliding movements to achieve adduction and abduction of the vocal folds. Internally, the laryngeal cavity is divided into the upper laryngeal vestibule (supraglottis), the middle part containing the laryngeal ventricle and vestibular (false vocal) folds, and the infraglottic cavity (subglottis). The fibroelastic intrinsic membranes include the quadrangular membrane superiorly, forming the vestibular ligaments, and the conus elasticus inferiorly, forming the crucial vocal ligaments (true vocal folds). The intrinsic muscles execute complex adjustments; notably, the posterior cricoarytenoids are the only muscles responsible for opening the rima glottidis (abduction), while the cricothyroids stretch the vocal folds to raise pitch. All intrinsic muscles are motor-innervated by the recurrent laryngeal nerve, except for the cricothyroid muscle, which receives its supply from the external branch of the superior laryngeal nerve. Phonation, the generation of sound, is explained by the aerodynamic-myoelastic theory, which describes how sustained subglottal air pressure forces adducted vocal folds open, followed by closure due to tissue elasticity and the low pressure created by the Bernoulli effect. Clinically, understanding the three paralumenal adipose tissue regions—the pre-epiglottic, paraglottic, and subglottic spaces—is essential for tracing the spread of laryngeal tumors. Tumors confined to the true vocal folds (glottis) often present with early hoarseness (dysphonia) because of the scarcity of lymphatics in the fold edges, distinguishing them from supraglottic tumors that metastasize more readily to the rich upper deep cervical lymph nodes.