The larynx is located within the anterior aspect of the neck, anterior to the inferior portion of the pharynx and superior to the trachea. Its primary function is to protect the lower airway by closing abruptly upon mechanical stimulation, thereby halting respiration and preventing the entry of foreign matter into the airway. Other functions of the larynx include the production of sound (phonation), coughing, the Valsalva maneuver, and control of ventilation, and acting as a sensory organ.
The larynx is composed of 3 large, unpaired cartilages (cricoid, thyroid, epiglottis); 3 pairs of smaller cartilages (arytenoids, corniculate, cuneiform); and a number of intrinsic muscles (see the image and video below). The hyoid bone, while technically not part of the larynx, provides muscular attachments from above that aid in laryngeal motion
The larynx is formed by a cartilaginous skeleton, which is held together by ligaments and membranes. The laryngeal muscles act to move the components of the larynx for phonation and breathing. More information about each of these structures can be found in their respective sections.
Anatomically, the internal cavity of the larynx can be divided into three sections:
- Supraglottis – From the inferior surface of the epiglottis to the vestibular folds (false vocal cords).
- Glottis – Contains vocal cords and 1cm below them. The opening between the vocal cords is known as rima glottidis, the size of which is altered by the muscles of phonation.
- Subglottis – From inferior border of the glottis to the inferior border of the cricoid cartilage.
The interior surface of the larynx is lined by pseudostratified ciliated columnar epithelium. An important exception to this is the true vocal cords, which are lined by a stratified squamous epithelium.
The arterial supply to the larynx is via the superior and inferior laryngeal arteries:
- Superior laryngeal artery – a branch of the superior thyroid artery (derived from the external carotid). It follows the internal branch of the superior laryngeal nerve into the larynx.
- Inferior laryngeal artery – a branch of the inferior thyroid artery (derived from the thyrocervical trunk). It follows the recurrent laryngeal nerve into the larynx.
Venous drainage is by the superior and inferior laryngeal veins. The superior laryngeal vein drains to the internal jugular vein via the superior thyroid, whereas the inferior laryngeal vein drains to the left brachiocephalic vein via the inferior thyroid vein.
The larynx receives both motor and sensory innervation via branches of the vagus nerve:
- Recurrent laryngeal nerve – provides sensory innervation to the infraglottis, and motor innervation to all the internal muscles of larynx (except the cricothyroid).
- Superior laryngeal nerve – the internal branch provides sensory innervation to the supraglottis, and the external branch provides motor innervation to the cricothyroid muscle.