Laryngeal Framework
The larynx forms the air passageway from the hyoid bone to the trachea. The larynx is continuous with the laryngopharynx superiorly and with the trachea inferiorly. The larynx provides a patent (open) airway and acts as a switching mechanism to route air and food into the proper channels. The larynx is commonly known as the voice box and provides the cartilaginous framework for vocal fold and muscle attachments, which vibrate to produce sound.
The hyoid bone consists of a body, two greater horns, and two lesser horns, and is the only bone that does not articulate with another bone. The hyoid bone is U-shaped and is suspended from the tips of the styloid processes of the temporal bones by the stylohyoid ligaments (Figure 28-1A and C). The hyoid bone is connected to the thyroid cartilage and supported by the suprahyoid and infrahyoid muscles and by the middle pharyngeal constrictor muscle. In addition, the hyoid bone supports the root of the tongue.
The framework of the larynx is an intricate arrangement of nine cartilages connected by membranes and ligaments (Figure 28-1A–C).
- Thyroid cartilage. The thyroid cartilage forms a median elevation, called the laryngeal prominence (“Adam’s apple”), and lies inferior to the hyoid bone. The thyroid cartilage typically is larger in males than in females because the male sex hormones stimulate its growth during puberty. The superior horn of the laryngeal cartilage is attached to the tip of the greater horn of the hyoid bone, whereas its inferior horn articulates with the cricoid cartilage, forming the cricothyroid joint.
- The thyrohyoid membrane, as its name implies, stretches between the thyroid cartilage and the hyoid bone. The superior laryngeal vessels and the internal laryngeal nerve pierce the membrane en route to providing vascular supply and sensory information, respectively, to the mucosa superior to the vocal folds.
- Cricoid cartilage. The cricoid cartilage is shaped like a signet ring, with the broad part of the ring facing posteriorly. The lower border marks the inferior limits of the larynx and pharynx. The function of the cricoid cartilage is to provide attachments for laryngeal muscles, cartilages, and ligaments involved in opening and closing of the airway to produce sound.
- Epiglottis. The epiglottis is elastic cartilage, shaped like a spoon, that is posterior to the root of the tongue. The lower end of the epiglottis is attached to the deep surface of the thyroid cartilage. When only air is flowing into the larynx, the inlet to the larynx is open wide, with the free edge of the epiglottis projecting superiorly and anteriorly. During swallowing, the larynx is pulled superiorly and the epiglottis tips posteriorly to cover the laryngeal inlet. As a result, the epiglottis acts as a deflector to keep food out of the larynx (and trachea) during swallowing.
- Arytenoid cartilages. The arytenoid cartilages are shaped like a pyramid. Their base articulates with the cricoid cartilage. Each arytenoid cartilage has a vocal process, which gives attachment to the vocal ligaments and vocalis muscle, and a muscular process, which gives attachment to the thyroarytenoid and the lateral and posterior cricoarytenoid muscles.
- Cuneiform and corniculate cartilages. These tiny cartilages lie on the apices of the arytenoid cartilages and are enclosed within the aryepiglottic folds.
From the vocal process of each arytenoid cartilage, a fibrous band extends anteriorly to attach to the deep surface of the thyroid cartilage (Figure 28-1C). These two fibrous ligaments are composed largely of elastic fibers and form the core of the mucosal folds called the vocal folds, or true vocal cords. Consequently, the vocal folds vibrate, producing sound as air rushes up from the lungs through the rima glottis, the opening between the vocal cords. Superior to the true vocal folds are a similar pair of mucosal folds, called the vestibular (false) vocal folds, which play no part in the production of sound because the false vocal folds are not opposable.
Function of the Larynx
Laryngeal muscles are innervated by the vagus nerve [cranial nerve (CN) X] and move the laryngeal skeleton. In turn, this movement changes the width and the tension on the vocal folds so that air passing between the vocal folds causes them to vibrate, producing sound.
