The thyroid cartilage is the largest of the nine laryngeal cartilages. The name -’thyroid’ comes from the Greek word thyreos which means shield-shaped. The thyroid cartilage is situated between the cricoid cartilage and the hyoid bone. It is composed of two identical halves (laminae) that meet at the midline and form the laryngeal prominence, popularly known as Adam's apple.
The thyroid cartilage is a firm and resilient structure, composed entirely of hyaline cartilage, which serves to protect and support the vocal cords. Additionally, it participates in the modulation of voice and serves as the attachment point for several ligaments and muscles of the larynx and neck.
This article will discuss the anatomy and function of the thyroid cartilage.
|Definition||Largest of laryngeal cartilages, located between the hyoid bone and cricoid cartilage|
|Histological structure||Hyaline cartilage|
|Surfaces and borders||Surfaces: external and internal
Borders: superior, inferior, posterior
|Main features||Laryngeal prominence, superior thyroid notch, paired thyroid laminae (superior thyroid horn, inferior thyroid horn, oblique line)|
|Function||Protection of larynx and vocal cords, modulation of voice, attachment point for several laryngeal/neck muscles|
The thyroid cartilage is a superficial structure, situated just beneath the skin and anterior to the laryngeal cavity.
It is located inferior to the hyoid bone and superior to the thyroid gland and cricoid cartilage.
The location and shape of the thyroid cartilage is of key importance to its function. More specifically, its superficial position make it the main protector of the delicate structures of the larynx such as the vocal cords.
As a whole, the thyroid cartilage has two surfaces (internal and external) and three borders/margins (superior, inferior and posterior). It is comprised of two identical flat parts known as the thyroid laminae. These are fused anteriorly along the midline to form a subcutaneous elevation known as the laryngeal prominence. In females, the laminae meet at an angle of approximately 120 degrees while in males, the angle is more acute at around 90 degrees. This smaller thyroid angle explains the more pronounced laryngeal prominence seen in males (the ‘Adam's apple’), longer vocal cords, and lower-pitched voice in males.
Along the superior border of the thyroid cartilage, the two laminae are separated by a V-shaped triangular space called the superior thyroid notch. A smaller, more shallow inferior thyroid notch can sometimes be appreciated in the middle of the lower border.
The posterior borders of the thyroid laminae elongate into superior and inferior projections known as the thyroid horns. The superior thyroid horn is longer and narrower than its inferior counterpart and is directed superiorly and posteromedially. Together with the entire superior margin of the thyroid cartilage, the superior horn is attached to the hyoid bone by the thyrohyoid membrane.
In contrast, the inferior thyroid horn is shorter and thicker and directed inferiorly and anteromedially. The inferior horn carries a small articular facet that articulates with the thyroid articular facet on the lateral side of the cricoid cartilage and forms the cricothyroid joint.
The superior thyroid tubercle is located anterior to the root of the superior horn, while the inferior tubercle is located on the inferior border of the thyroid lamina. Running anteroinferiorly between these landmarks on the external surface of each lamina is a ridge known as the oblique line. This serves as the attachment point for the sternothyroid, thyrohyoid and thyropharyngeal part of the inferior pharyngeal constrictor muscle.
The internal surface of the thyroid cartilage is covered by a mucous membrane. The angle serves as the attachment point for several laryngeal ligaments and muscles such as the thyroepiglottic, vestibular and vocal ligaments as well as the thyroarytenoid, thyroepiglottic and vocalis muscles.
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Due to its rigid structure, the main function of the thyroid cartilage is to form the anterior wall of the larynx and protect the structures located posterior to it, mainly the muscles of the larynx and vocal cords. The thyroid cartilage also participates in the modulation of voice (changing the pitch) through the movements at the cricothyroid joint. Additionally, this cartilage is the attachment for several muscles of the larynx and neck region.
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