Master Pharyngeal Arch Derivatives: 4-6 Arches

Thyroid cartilage is the largest of the cartilaginous members of the larynx and serves to protect the vocal cords. It is shaped by two flaps that come together, joining at the midline and forming what is called the midline prominence, or Adam's apple. The indent created above this midline prominence is called the superior thyroid notch.

The cricoid is a signet ring-shaped cartilage that lies inferior to the thyroid cartilage. It is the only laryngeal cartilage that forms a complete ring. It serves as an attachment site for the structures that open and close the airway.

The arytenoid cartilage is shaped like a three-pronged hat and acts as a lever to allow vocal cord movement.

The corniculate cartilage are a pair of cartilage that articulate with the arytenoid cartilages to extend them posteriorly and medially.

The cuneiform cartilages are paired cartilages that sit on top of and move with the arytenoids. They function to support the vocal folds and lateral aspects of the epiglottis.

The cricothyroid tenses and adducts the vocal cords, resulting in higher-pitch phonation. It is derived from the fourth pharyngeal arch and is the only intrinsic laryngeal muscle supplied by the superior laryngeal nerve, a branch of CN X (vagus).

The muscular wall of the pharynx is composed of the superior, middle and inferior constrictor muscles. These serve to constrict the pharynx. They are derived from the fourth pharyngeal arch and are therefore innervated by the superior laryngeal nerve, a branch of CN X.

The intrinsic muscles of larynx control sound production. With the exception of the cricothyroid, all intrinsic muscles of the larynx are innervated by the recurrent laryngeal branch of CN X (vagus).

CN X, also known as the vagus nerve, is a motor, sensory and visceral nerve with several functions such as heart rate regulation, respiratory drive regulation, palate elevation, swallowing, and talking.

The superior laryngeal nerve descends next to the pharynx and divides into external and internal branches. The external branch supplies the cricothyroid muscle. The internal branch supplies sensory innervation to the larynx above the vocal cords.

CN X, also known as the vagus nerve, is a motor, sensory and visceral nerve with several functions such as heart rate regulation, respiratory drive regulation, palate elevation, swallowing, and talking.

The recurrent laryngeal branch of CN X (vagus) supplies sensory innervation below the vocal cords, and motor innervation to all laryngeal muscles except the cricothyroid. Injury to this nerve due to surgery, trauma, or mass lesion may result in difficulty speaking and a hoarse voice.