The term glottis refers to the vocal apparatus of the larynx, which consists of the true vocal folds (vocal cords) and the opening between the vocal cords, called the rima glottidis. The glottis is located in the middle part of the laryngeal cavity, between the supraglottis and subglottis. The glottis is concerned with sound production. The vibration of the vocal folds when air is forced through the rima glottidis produces sound.
The glottis is entirely different from the epiglottis, which is a leaf-shaped, elastic cartilage structure covered with mucous membrane. The epiglottis closes off the laryngeal inlet during swallowing to prevent materials from entering the airway.
This article will discuss the anatomy and function of the glottis.
|Vocal folds and rima glottidis|
|Location||The glottis is the middle subsection of the larynx, located between the supraglottis and subglottis|
|Blood supply||Inferior laryngeal artery|
|Innervation||Inferior laryngeal nerve|
|Functions||Control of sound production, air conduction|
The glottis is composed of the vocal folds and the opening between them called the rima glottidis. It is located in the interior of the larynx between the supraglottis and subglottis. The supraglottis refers to the region of the larynx between the base of the tongue and the vocal cords, while the subglottis is the part of the larynx that lies just inferior to the vocal cords down to the tracheal opening. These terms are clinically important for indicating the exact location of lesions within the laryngeal cavity.
Specifically, the glottis lies just inferior to the paired vestibular folds at the entrance of the middle part of the laryngeal cavity. The vestibular folds are folds of the mucous membrane which cover the vestibular ligaments. The vestibular folds are also called “false vocal cords” because they do not play a role in sound production, but instead protect the true vocal cords. The triangular opening between the two adjacent vestibular folds is called the rima vestibuli, and is continuous with the rima glottidis. The lateral walls of the laryngeal cavity between the vestibular and vocal folds bulge outward to form lateral pouches called laryngeal ventricles.
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The vocal folds are wedge-shaped folds of mucous membrane that project medially from the lateral walls of the middle part of the laryngeal cavity, inferior to the vestibular folds. Each vocal fold consists of a vocal ligament and a vocalis muscle and the overlying mucosa which covers it. The vocal ligament is the thickened, medial free edge of the conus elasticus (cricothyroid membrane) that extends from the posterior surface of the thyroid cartilage to the vocal processes of the arytenoid cartilages. The vocalis muscle arises from the vocal process of the arytenoid cartilage and runs parallel to and inserts along the length of the vocal ligament. Its function is to adjust the tension in the vocal folds.
The vocal folds receive both sensory and motor innervation from the inferior laryngeal nerve, the terminal part of recurrent laryngeal nerve, from the vagus nerve (CN X). The arterial supply to the vocal folds is by the inferior laryngeal artery, a branch of the inferior thyroid artery, which accompanies the inferior laryngeal nerve.
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The rima glottidis refers to the narrow, triangular opening between the two adjacent vocal folds. This opening is continuous with the rima vestibuli above and leads into the infraglottic cavity below. The shape of this opening changes depending on the type of activity the larynx is involved in, which determines the position of the vocal folds. Rotational movements of the arytenoid cartilages at the cricoarytenoid joints can separate (abduct) the vocal folds, widening the rima glottidis or appose (adduct) the vocal folds and narrow the rima glottidis.
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The vocal folds are called the “true vocal cords” because they are responsible for sound production. This is achieved by vibrations of the free edges of the vocal folds when air is forced through the rima glottidis. The quality of sound produced depends on the length, tension and position of the vocal folds. The vocal folds also act as the primary inspiratory laryngeal sphincter when they are closed, to block the passage of air.
During regular breathing at rest, the rima glottidis is a narrow wedge shape, but during forced respiration it is a wide triangular shape and the vocal cords are as far apart as they can extend. During phonation, the vocal cords close and the rima glottis is slit-like.
A singer’s nodule is the common name for a benign laryngeal polyp. These are usually small and are caused by overuse of the vocal cords or incessant smoking, which leads to chronic irritation. In most cases, the inflammation is limited to the true vocal cords, however this disorder has been known to extend to the adjacent structures also. It is significant because if it is on the medial side of a cord, it will obstruct the closure of the cords and create an imbalance of vocal pitch when speaking. Rest is key during the rehabilitation phase.
Glottis: want to learn more about it?
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