Thyroid Cartilage: Structure and Functions

What is Thyroid Cartilage? 

The thyroid cartilage is the most prominent and largest cartilage of the larynx and is composed of hyaline cartilage. This thyroid cartilage has two wings, called ala of the thyroid cartilage. In females, the sides join at approximately 120 degrees; in males, the angle is closer to 90 degrees. This smaller thyroid angle explains the greater laryngeal prominence, longer vocal

cords, and lower-pitched voice in males. Vocal cords are more extended in males and shorter in females.

On the inner side of this fusion line are attached the vestibular ligaments and, below them, the vocal ligaments. The superior (more significant) and inferior (lesser) cornua of the thyroid are slender, posteriorly directed extensions of the edges of the lamina. The lateral thyrohyoid ligament attaches the superior cornu to the hyoid bone, and the cricoid cartilage articulates with the inferior cornu at the cricothyroid joint. On the thyroid ala, there is oblique line which gives attachment to the following muscles

• Sternothyroid
• Thyrohyoid muscles
• Thyropharyngeus muscles

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Differentiate Superior Cornu Inferior Cornu

Thyropharyngeus is the part of the inferior constrictor muscle. The inferior pharyngeal constrictor muscle consists of two distinct sections. The upper portion, known as the thyropharyngeal part, originates from the thyroid cartilage. 

Meanwhile, the lower section, termed the cricopharyngeal part, derives its attachment from the cricoid cartilage. The anterior border of each thyroid lamina fuses with its partner at an angle of 90° and 120° in women. The shallower angle in men is associated with the Larger

laryngeal prominence (Adam's apple) The greater length of the vocal cords and the resultant deeper pitch of the voice.

Cricoid Cartilage

The cricoid cartilage is the only complete ring of cartilage around the trachea. Anteriorly, there is a narrow arch, and posteriorly, there is a wide lamina. The cricoid cartilage is attached superiorly to the thyroid cartilage via the cricothyroid membrane and inferiorly to the trachea via the crico-tracheal membrane.

Cricoid Arch

Vertically narrow in front (5-7 mm in height) and widen posteriorly towards the lamina.

Cricothyroid is attached to the external aspect of its front and sides; it is the tensor of the vocal cord and has a secondary adduction function as well, and cricopharyngeus (part of the inferior pharyngeal constrictor) is attached behind cricothyroid.

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Cricoid Lamina

The cricoid lamina is approximately quadrilateral in outline and 2-3 cm in vertical dimension.

It bears a posterior median vertical ridge. The two fasciculi of the longitudinal layer of esophageal muscle fibres (muscularis externa) are attached by a tendon to the upper part of the ridge.

Posterior cricoarytenoid attaches to a shallow depression on either side of the ridge. The posterior cricoarytenoid is the only abductor of the vocal cord. The cartilage serves as a point attachment for various muscles, cartilages, and ligaments that play essential roles in both regulating the airway and facilitating speech production.

Cricoarytenoid joint: joint between the cricoid and arytenoid cartilage. Its functions are essential, as it tells about the movement of vocal cords during phonation and respiration.

Cricothyroid joint: Joint between the inferior horn of thyroid cartilage and cricoid cartilage

Cricothyroid joint: The synovial joint between the inferior cornua of the thyroid cartilage and the sides of the cricoid cartilage.

Arytenoid Cartilage

Articulate with the lateral parts of the superior border of the cricoid lamina. This cartilage is pyramidal in shape. It has 3 surfaces: anterior, Medial, and posterior surfaces It includes two major processes: Muscular and Vocal Process

• Vocal process: Between thyroid cartilage and vocal process, the vocal ligament of the vocal cord is attached.
• Muscular process: It gives attachment to Lateral and posterior cricoarytenoid muscle

It has a base and apex.

• Base: It rest on the superior facet of cricoid cartilage.
• Apex: It gives attachment to corniculate and cuneiform cartilage.

The anterolateral surface is somewhat convex and rough. It has two depressions. The first one (above) is for the vestibular ligament, which forms the false cord. The second one (below) is for the vocal ligaments. Its lateral angle is called the muscular process, and the anterior angle is called the vocal process. It articulates with the cricoid lamina with a ball-and-socket joint.

The posterior surface, which is triangular, smooth, and concave, is covered by transverse arytenoid. The medial surface is narrow, smooth, and flat. It is covered by mucosa, and its lower edge forms the lateral boundary of the intercartilaginous part of the rima glottidis.

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Cricoarytenoid Joint

This joint is in between the facets on the lateral parts of the upper border of the lamina of the cricoid cartilage and the bases of the arytenoids. This joint is responsible for the movements such as:

• Rotate about an oblique axis—the vocal process swings laterally or medially, thereby increasing or decreasing the width of the rima glottidis.
• Gliding movement, by which the arytenoids approach or recede from one another.

The posterior cricoarytenoid ligaments limit forward movements of the arytenoid cartilages on the cricoid cartilage. It has been suggested that the 'rest' position of the cricoarytenoid ligament is a major determinant of the position of a denervated vocal cord.

Corniculate Cartilage

It is made of two conical nodules of elastic fibrocartilage. This cartilage articulates with the apices of the arytenoid cartilages, prolonging them posteromedially. They lie in the posterior parts of the aryepiglottic mucosal folds and are sometimes fused with the arytenoid cartilages.

Cuneiform Cartilage

It is made of two small, elongated, club-like nodules of elastic fibrocartilage. One in each aryepiglottic fold anterosuperior to the corniculate cartilages and are visible as whitish elevations through the mucosa.

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Hope you found this blog helpful for your ENT residency Larynx Preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs.