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.
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 :)
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