The Larynx

Hello :) In this post, we'll discuss the anatomy of the larynx including the airway itself, its cartilages, ligaments and muscles.

Airway

The laryngeal cavity is known as the aditus larynges. The inlet to this cavity leads into a wide chamber known as the vestibule of the larynx. The middle portion of the larynx is called the glottis and is surrounded by the arytenoid cartilages dorsally and the vocal folds ventrally. This narrows to form the glottic cleft which is a narrow passageway that runs towards the trachea. In the dog and horse, as the glottic cleft moves caudally, it opens laterally to form two lateral laryngeal ventricles. 

Cartilages

The larynx contains four types of cartilages: the epiglottis, the thyroid, the cricoid and arytenoids. All are unpaired except for the arytenoids.

The epiglottis folds back to cover the glottis (the opening to the larynx) during swallowing. The cricoid is ring-shaped and is the only cartilage to surround the larynx completely. The thyroid forms the “Adam’s apple” in people. Rostrally, the thyroid cartilage articulates with the thyroid bone of the hyoid apparatus, and caudally it articulates with the arch of the cricoid. The arytenoids control the vocal folds by rotating.

Ligaments

The cricothyroid ligament connects the ventrocaudal part of the thyroid cartilage to the ventral arch of the cricoid cartilage.

The cricotracheal ligament connects the larynx with the first tracheal cartilage.

The vocal ligament extends from the vocal processes of the arytenoids to either side of the body of the thyroid. It forms the basis of the vocal fold.

In animals that have a vestibular fold, a vestibular ligament exists rostral to the vocal ligament.

Muscles

Intrinsic Musculature

The intrinsic muscles contract to narrow or widen the glottic cleft which tenses or relaxes the vocal folds. All are innervated by the recurrent laryngeal nerve except for the cricothyroid muscle which is innervated by the cranial laryngeal nerve.

The cricothyroid muscle extends between the lateral surfaces of the cricoid and thyroid cartilages. It is innervated by the cranial laryngeal nerve. It tenses the vocal folds when it contracts.

The dorsal cricoarytenoid is the main abductor of the vocal folds and widens the glottic cleft. It extends from the dorsal surface of the cricoid to the muscular process of the arytenoid. A lateral cricoarytenoid also exists and this extends from the cricoid arch and the muscular process of the arytenoid cartilages. When this contracts, it narrows the glottic cleft.  

The transverse arytenoid connects the muscular processes of each arytenoid to each other. It adducts the two arytenoid cartilages and narrows the glottic cleft.  

The thyroarytenoid extends from the base of the glottis and thyroid cartilage to the muscular and vocal processes of the arytenoid cartilage. They increase the tension of the vocal folds and narrow the glottic cleft. 

And that's it! See you next time :)