The larynx lies within the anterior aspect of the neck, anterior to the lower pharynx, and superior to the trachea.
Its main function is to protect the lower airways by closing abruptly with mechanical stimulation, thus stopping breathing and preventing the entry of foreign matter into the airways.
Other functions of the larynx include sound production (phonation), coughing, the Valsalva maneuver, and control of ventilation, and it acts as a sensory organ.
The larynx is composed of 3 large and unpaired cartilages (cricoid, thyroid, epiglottis); 3 pairs of smaller cartilages (arytenoid, corniculate, cuneiform); and a number of intrinsic muscles.
The hyoid bone, although not technically part of the larynx, provides muscle attachments from above that aid in laryngeal movement.
Cartilages of the larynx
The cricoid cartilage is a ring of hyaline cartilage located on the underside of the larynx and is the only complete ring of cartilage around the trachea.
It is shaped like a “signet ring,” with a wide portion posterior to the airway (cricoid cartilage sheet) and a narrower portion surrounding it anteriorly (cricoid cartilage arch).
The posterior surface of the lamina contains 2 oval depressions, which serve as attachment sites for the posterior cricoarytenoid muscles, separated by a vertical midline border that serves as attachment to the esophagus.
At the junction of the lamina with the arch, there are small round articular facets on the external posterolateral surface of each side of the annulus that articulate with the inferior horn of the thyroid cartilage. The lower border of the cricoid cartilage is connected to the first tracheal ring by the cricotracheal ligament.
The superior border of the cricoid cartilage attaches to the cricothyroid ligament in the anterior midline, the cricothyroid muscles on the lateral aspects, and the bases of a pair of arytenoid cartilages on both sides of the posterior aspect.
The thyroid cartilage is the largest of the laryngeal cartilages. It is formed by right and left plates that separate posteriorly and join at an acute angle in the anterior midline, forming the laryngeal prominence, commonly known as the Adam’s apple.
Laryngeal prominence is more evident in men, because the angle between the 2 blades is sharper in men (90 °) than in women (120 °).
The superior thyroid notch is a V-shaped notch immediately above the laryngeal prominence, while the inferior thyroid notch is less defined and is located in the midline along the base of the cartilage.
The 2 blades are quadrilateral in shape and form the lateral surfaces of the thyroid cartilage that extend obliquely to cover each side of the trachea.
The posterior aspect of each lamina is elongated to form an upper horn and a lower horn. The medial surfaces of the lower horns articulate with the external posterolateral surface of the cricoid cartilage.
The lower border of the thyroid cartilage is attached to the cricoid cartilage by the cricothyroid membrane in the midline and the cricothyroid muscles on both sides. The superior horn along with the entire superior border of the thyroid cartilage is attached to the hyoid bone by the thyrohyoid membrane.
The epiglottis is a sheet-like cartilage that moves downward to form a lid over the glottis and protect the larynx from the aspiration of swallowed food or liquids.
It is attached by its stalk to the midline of the medial aspect of the thyroid cartilage, approximately midway across the angle of the laryngeal prominence and the inferior notch.
It is attached through the thyroepiglottic ligament and projects superiorly to cover the upper opening of the larynx. The midline of the upper surface of the epiglottis is also attached to the body of the hyoid bone through the hyoepiglottic ligament.
The mucous membrane covering the upper anterior part of the epiglottis is reflected on the sides of the epiglottis, giving rise to the glossoepiglottic folds.
Aryepiglottic folds are folds of mucosa on the posterior surface of the epiglottis. The depressions on both sides of the median fold, between the root of the tongue and the epiglottis, are called epiglottic valécules .
The arytenoid cartilages form the part of the larynx to which the vocal ligaments and vocal cords attach. They are pyramidal in shape and have 3 surfaces, a base and an apex.
They are located above the cricoid cartilage in the posterior part of the larynx, with the base of the arytenoid cartilages articulating on each side with the posterior aspect of the superior border of the cricoid lamina.
The anterior angle of the base of the arytenoid cartilage is elongated to form a vocal process for the attachment of the vocal ligament, while the lateral angle is elongated to form a muscular process for the attachment of the posterior and lateral cricoarytenoid muscles.
The posterior surface of the arytenoid cartilage gives attachment to the arytenoid muscle. The anterolateral surface has 2 depressions to join the false vocal cord (vestibular ligament) and the vocalis muscle.
The medial surface has a mucosal lining that forms the lateral aspect of the respiratory part of the glottis. The apex of the arytenoid cartilage is pointed and articulates with the corniculate cartilage.
The corniculate cartilages are 2 small conical cartilages that articulate with the apices of the arytenoid cartilages, and serve to extend them backwards and inwards. They are found in the posterior parts of the aryepiglottic folds of the mucous membrane.
Cuneiform cartilages are 2 small, rod-shaped cartilages that lie ahead of the corniculate cartilages in the aryepiglottic folds. They form small whitish elevations on the surface of the mucous membrane, just anterior to the arytenoid cartilages.