- The larynx, commonly known as the voice box, is a complex cartilaginous and muscular structure located in the neck, anterior to the pharynx and superior to the trachea.
- It plays essential roles in respiration, phonation (voice production), and airway protection during swallowing. Anatomically, the larynx is situated at the level of the third to sixth cervical vertebrae and connects the upper airway (pharynx) to the lower respiratory tract (trachea).
- It is composed of a framework of cartilages, intrinsic and extrinsic muscles, ligaments, and mucosal lining, all coordinated to enable its diverse functions.
- The laryngeal framework consists of nine cartilages: three unpaired (thyroid, cricoid, and epiglottis) and three paired (arytenoid, corniculate, and cuneiform). The largest, the thyroid cartilage, forms the anterior wall and is most prominent in the midline as the “Adam’s apple.” The cricoid cartilage sits below the thyroid and forms a complete ring around the airway. The epiglottis, a leaf-shaped cartilage, acts as a flap that covers the laryngeal inlet during swallowing, preventing aspiration of food into the lungs. The paired arytenoid cartilages are particularly important because they anchor the vocal folds and facilitate their movement during speech and breathing.
- Within the larynx lie the vocal folds (true vocal cords), which are essential for sound production. These are composed of a layered structure including an outer epithelial lining, the lamina propria (with three sublayers: superficial, intermediate, and deep), and the thyroarytenoid muscle at the core. When air from the lungs is forced through the glottis—the space between the vocal folds—the folds vibrate, producing sound. The pitch and quality of the voice are modulated by tension and length adjustments of the vocal folds, controlled by the intrinsic laryngeal muscles, such as the cricothyroid and thyroarytenoid.
- In addition to phonation, the larynx serves a critical role in protecting the lower respiratory tract. During swallowing, a coordinated action of the laryngeal muscles and the elevation of the larynx closes the glottis and draws the epiglottis over the airway, effectively sealing it. This mechanism prevents the entry of food and liquids into the lungs. Any disruption in this protective reflex can lead to aspiration and potentially life-threatening respiratory infections.
- The larynx is also important in respiratory regulation. It controls the resistance of airflow into the trachea and lungs through the opening and closing of the glottis. During quiet breathing, the vocal folds are relaxed and apart; during forced breathing or exertion, the glottis widens to allow increased airflow. In contrast, the glottis can be tightly closed during activities like coughing, Valsalva maneuver (as in lifting heavy objects), and phonation, to generate subglottic pressure.
- The innervation of the larynx is primarily through branches of the vagus nerve (cranial nerve X), specifically the superior laryngeal nerve (external and internal branches) and the recurrent laryngeal nerve. These nerves provide motor control to the intrinsic muscles and sensory innervation to the mucosa. Damage to the recurrent laryngeal nerve, which can occur during thyroid surgery or due to tumors, may lead to vocal fold paralysis, hoarseness, or breathing difficulties.
