The upper airway consists of the nose, mouth, pharynx, larynx, trachea, and mainstem bronchi. The laryngeal structures in part serve to prevent aspiration into the trachea. There are two openings to the human airway: the nose, which leads to the nasopharynx, and the mouth, which leads to the oropharynx. These passages are separated anteriorly by the palate, but they join posteriorly in the pharynx (Figure 14–1). The pharynx is a U-shaped fibromuscular structure that extends from the base of the skull to the cricoid cartilage at the entrance to the esophagus. It opens anteriorly into the nasal cavity, the mouth, the larynx, and the nasopharynx, oropharynx, and laryngopharynx, respectively. At the base of the tongue, the epiglottis functionally separates the oropharynx from the laryngopharynx (or hypopharynx). The epiglottis prevents aspiration by covering the glottis—the opening of the larynx—during swallowing. The larynx is a cartilaginous skeleton held together by ligaments and muscle. The larynx is composed of nine cartilages (Figure 14–2): thyroid, cricoid, epiglottic, and (in pairs) arytenoid, corniculate, and cuneiform. The thyroid cartilage shields the conus elasticus, which forms the vocal cords.
Anatomy of the airway. (Reproduced with permission from Butterworth JF, Mackey DC, Wasnick JD (eds). Morgan & Mikhail’s Clinical Anesthesiology, 7e. New York, NY: McGraw Hill; 2022.)
Cartilaginous structures comprising the larynx. (Used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.)
The sensory supply to the upper airway is derived from the cranial nerve. The vagus nerve (cranial nerve X) provides sensation to the airway below the epiglottis. The superior laryngeal branch of the vagus divides into an external (motor) nerve and an internal (sensory) laryngeal nerve that provide sensory supply to the larynx between the epiglottis and the vocal cords. Another branch of the vagus, the recurrent laryngeal nerve, innervates the larynx below the vocal cords and the trachea.
The muscles of the larynx are innervated by the recurrent laryngeal nerve, with the exception of the cricothyroid muscle, which is innervated by the external (motor) laryngeal nerve, a branch of the superior laryngeal nerve. The posterior cricoarytenoid muscles abduct the vocal cords, whereas the lateral cricoarytenoid muscles are the principal adductors.
Unilateral denervation of a cricothyroid muscle causes very subtle clinical findings. Bilateral palsy of the superior laryngeal nerve may result in hoarseness or easy tiring of the voice, but airway control is not jeopardized.
Unilateral injury to a recurrent laryngeal nerve results in paralysis of the ipsilateral vocal cord, degrading voice quality. Assuming that the superior laryngeal nerves are intact, acute bilateral recurrent laryngeal nerve palsy can result in stridor and respiratory distress because of the remaining unopposed tension of the cricothyroid muscles. Airway problems ...