Description

The larynx connects the inferior pharynx with the trachea and, in so doing, serves three functions (Box 51-1): to maintain a patent airway, to guard against aspiration of liquids or solids into the trachea, and to permit vocalization. It is about 5 cm in length and, in adults, lies at the level of C4 to C5. In cross-section at the level of the laryngeal prominence (Adam’s apple), the larynx is triangular because of the shape of the thyroid cartilage. At the level of the cricoid cartilage, the larynx becomes more round. The larynx provides the area of greatest resistance to passage of air to the lungs.

Laryngeal skeleton

The laryngeal skeleton has a total of nine cartilages (Table 51-1): three sets of paired cartilages (arytenoids, corniculates, cuneiforms) and three unpaired cartilages (thyroid, cricoid, and epiglottic) (Figure 51-1).

Joints, ligaments, and membranes of the larynx

The joints of the larynx include the cricothyroid joint, which provides articulation between the lateral surfaces of the cricoid cartilage and the inferior horns of the thyroid cartilage, and the cricoarytenoid joint, which provides articulation between the bases of the arytenoid cartilage and the upper surface of the cricoid lamina. The thyrohyoid membrane is an extrinsic ligament that connects the thyroid cartilage to the hyoid bone. The larynx includes three sets of ligaments: the cricothyroid and cricotracheal, which connect the cricoid to the thyroid cartilage and first tracheal ring, respectively; the vocal ligament, which extends from the thyroid cartilage to the arytenoid cartilage; and the vestibular ligament, which extends from the thyroid cartilage to the arytenoid cartilage above the vocal fold.

Interior of the larynx

The three divisions of the interior of the larynx include the vestibule, above the vestibular folds (false cords); the ventricle, between the vestibular folds above and the vocal folds (cords) below; and the infraglottic cavity, from the vocal folds to the tracheal cavity.

The vocal folds (vocal cords) consist of the vocal ligament, conus elasticus, vocalis muscle fibers, and a covering of mucous membrane. The rima glottidis is the opening between the vocal folds. The glottis comprises the vocal folds, the rima glottidis, and the narrow part of the larynx at the level of the vocal folds.

The vestibular folds are ligaments covered by folds of mucous membrane. They meet during swallowing to prevent aspiration. The rima vestibuli is the space between the false cords.

Innervation

Innervation to the larynx is supplied by the superior laryngeal nerve (Figure 51-2), a branch of the vagus nerve (X). This nerve has two terminal branches: the internal laryngeal nerve, which is purely sensory and has fibers from the mucosa of the tongue to the vocal folds (including the superior surface of these folds) and the external laryngeal nerve, which is purely motor and innervates the cricothyroid muscle. Another branch of cranial nerve X, the recurrent laryngeal nerve, provides branches to all of the muscles of the larynx, except the cricothyroid, and provides sensory innervation below the vocal cords. Its terminal branch, the inferior laryngeal nerve, has anterior and posterior branches.

Muscles

The extrinsic muscles comprise depressors and elevators (Box 51-2), which move the larynx as a whole. The intrinsic muscles, which are considered as functional groups, include the abductors and adductors. The abductors (the arytenoid muscle, aryepiglottic muscle, transverse arytenoid muscle, oblique arytenoid muscle, and thyroepiglottic muscle) open the inlet to the larynx and the adductor (lateral cricoarytenoid muscle) closes the vocal folds.

Blood supply

The superior laryngeal artery is a branch of the superior thyroid artery off the external carotid artery. The inferior laryngeal artery is a branch of the inferior thyroid artery off the thyrocervical trunk off the subclavian artery.

Considerations with the infant larynx

The infant’s larynx is more anterior than the adult’s. The cricoid cartilage is at the level of C3 to C4 in the infant, compared with C4 to C5 in the adult. The infant’s epiglottis is relatively longer, stiffer, and further away from the anterior pharyngeal wall, as compared with the adult epiglottis. The narrowest point is at the level of the cricoid cartilage. The tongue of an infant is relatively larger than the tongue of an adult.