The anatomy of the larynx is complicated. It lies inferior to the hyoid bone, anterior to the lower pharynx and joins to the top of the trachea at C6 level.
Three unpaired cartilages make up its external form:
(1) epiglottis (a flap of elastic cartilage covered by mucous membrane which is attached to the anterior thyroid cartilage)
(2) thyroid cartilage; and
(3) cricoid cartilage (most inferior and separated from the thyroid cartilage above by the cricothyroid membrane).
The three paired cartilages (the arytenoids, corniculate and cuneiform) are smaller, located posteriorly within the larynx, and function in movement of the vocal cords.
The extrinsic muscles of the larynx (infrahyoid, suprahyoid and stylopharangeus) move the larynx as a whole during swallowing. The intrinsic muscles (the arytenoids, cricoarytenoids, thyroarytenoids and cricothyroid) abduct, adduct, relax and tense the vocal cords during speech and respiration. The vocal cords are relaxed and abducted during respiration and adducted and tensed during phonation.
During swallowing the backward movement of the tongue and upward movement of the larynx forces the epiglottis down over the superior laryngeal opening to prevent swallowed matter from entering the trachea.
The vagus nerve (CN X) provides motor and sensory innervation to the larynx via its superior laryngeal branch (motor to cricothyroid and sensory to the superior larynx above the vocal cords), and its recurrent laryngeal branch (motor to all the intrinsic muscles of the larynx except cricothyroid and sensory to the larynx below the vocal cords).