Larynx

Function of the Larynx

The larynx is situated at the upper end of the trachea, connecting the lungs to the vocal tract. It has two main functions:

• The first, and most important with respect to maintaining one’s health status, is as a valve. Thus, during the act of swallowing the larynx is closed, thereby ensuring that food passes safely into the esophagus and down into the stomach, rather than entering the lungs.

• The second function, and more important to the theme of this website, is as a source of sound to be used in speech.

Laryngeal Cartilages

The larynx is constructed from nine cartilages. For the purpose of this discussion, however, we will restrict ourselves to a consideration of just three of these:

• thyroid cartilage

• cricoid cartilage

• arytenoid cartilages

The thyroid cartilage is the largest of the laryngeal cartilages and forms the major chamber of the larynx. It is constructed from two relatively flat quadrilateral (four-sided) plates that are fused anteriorly in the midline along most of their length into a characteristic shield shape. The angle at which the plates join is different in males and females. In males it is about 90^o and in females it is nearer 120^o. This so-called thyroid angle is, therefore, more acute in men and it is consequently more noticeable as the Adam’s Apple. Posteriorly each plate is extended both upwards and downwards into horns or cornu. The superior horns attach by ligaments to the hyoid bone, situated under the base of the tongue in the neck, and the inferior horns articulate with the cricoid cartilage beneath.

The cricoid cartilage, therefore, forms the base of the larynx. It is a complete ring of cartilage that extends upwards posteriorly to form a plate. The inferior horns of the thyroid cartilage sit on the cricoid cartilage at this posterior position. This articulation allows the cricoid cartilage to be tilted by an angle of up to 15^o downwards and away from the lower anterior border of the thyroid cartilage. The cricoid cartilage is connected underneath to the upper trachea by the crico-tracheal ligament. We see, therefore, that both the thyroid cartilage and cricoid cartilages are individual cartilages (see Figure 1).

Figure 1. Human Larynx

The third major cartilage construction in the larynx is actually a pair of cartilages known as the arytenoid cartilages. These are pyramid-shaped and they are situated on the upper posterior part of the cricoid cartilage. One is placed laterally to the left and one laterally to the right. The arytenoids can be moved in rotational and sliding movements that are used to control the movement of the attached vocal cords.