Intrinsic Muscles

INTRINSIC LARYNGEAL MUSCLES

Individual components of the larynx are acted on by the intrinsic laryngeal muscles. They regulate the length and tension of the vocal folds, as well as the form of the rima glottidis (the aperture between the vocal folds and the arytenoid cartilages). They also make fine adjustments to the vocal mechanism itself. (Bernes et al., 2020).

The intrinsic laryngeal muscles can be divided into the following:

Adductors
Abductors
Tensors
Relaxers
Auxiliaries

ADDUCTORS

Adductors are responsible for adduction (coming or closing together of the vocal folds to close the glottis). The adductors are the lateral cricoarytenoid, transverse arytenoid, and the oblique arytenoid.

Lateral Cricoarytenoid Muscle

The lateral cricoarytenoid muscle originates from the superior-lateral surface of the cricoid cartilage. It courses superiorly-posteriorly. Its insertion is in the muscular process of the arytenoids. It is innervated by the Cranial Nerve X (Vagus Nerve), specifically the recurrent laryngeal nerve. Its function is to adduct the vocal folds, thereby increasing medial compression.

Transverse Arytenoid Muscle

The transverse arytenoid muscle originates from the superior-lateral margin of the posterior arytenoid. It courses laterally. This spans from one arytenoid cartilage to the opposite arytenoid.Its insertion is in the lateral margin of the posterior surface; opposite arytenoid. It is innervated by the Cranial Nerve X (Vagus Nerve), specifically the recurrent laryngeal nerve. Its function is to adduct the vocal folds.

Oblique Arytenoid Muscle

The oblique arytenoid muscle originates from the posterior base of the muscular process. It courses superiorly-obliquely. Its insertion is in the apex of the opposite arytenoids. It is innervated by the Cranial Nerve X (Vagus Nerve), specifically the recurrent laryngeal nerve. Its function is to pull the apex medially.

ABDUCTORS

The abductors are responsible for the opening of the vocal folds. They move the vocal folds away from each other by pulling the back portion of the arytenoid cartilages together. In the laryngeal system, there is only one type of vocal fold abductor: the posterior cricoarytenoid muscles.

Posterior Cricoarytenoid Muscle

Vocal fold abduction would not happen without the presence of the posterior cricoarytenoid muscle since this is the only abductor muscle. It originates from the posterior cricoid lamina, then it courses superiorly. Its insertion is in the posterior aspect of the arytenoids. Its functions are to rock the arytenoid cartilages laterally and to abduct the vocal folds.

TENSORS

The tensors tense the vocal folds. The tensor muscles of the larynx are the thyrovocalis muscle, cricothyroid (pars recta), and the cricothyroid (pars oblique).

Medial Thyroarytenoid Muscle or Thyrovocalis Muscle

The thyrovocalis muscle originates from the inner surface of the thyroid cartilage near the notch. It courses posteriorly. Its insertion is on the lateral surface of the arytenoid vocal process. It is innervated by the recurrent laryngeal nerve of the Cranial Nerve X (Vagus Nerve). It functions to tense the vocal folds.

Cricothyroid, Pars Recta

The Cricothyroid, Pars Recta originates from the anterior surface of the cricoid cartilage beneath the arch. It courses superiorly and externally. Its insertion is on the lower surface of the thyroid lamina. It is innervated by the external branch of the superior laryngeal nerve of the Cranial Nerve X (Vagus Nerve). Its function is to depress the thyroid relative to the cricoid and to tense the vocal folds.

Cricothyroid, Pars Oblique

The Cricothyroid, Pars Oblique originates from the cricoid cartilage lateral to the pars recta. It courses superiorly and obliquely. Its insertion is on the thyroid cartilage between the laminae and inferior horns. It is innervated by the external branch of the superior laryngeal nerve of the Cranial Nerve X (Vagus Nerve). Its function is to depress the thyroid relative to the cricoid and to tense the vocal folds.

RELAXER

The relaxer serves as the direct opposite of the tensor. It relaxes the vocal ligament and allows a softer voice to be produced.

There is only one laryngeal relaxer muscle. This muscle is known as the Thyromuscularis Muscle. The Thyromuscularis Muscle originates from the inner surface of the thyroid cartilage near the crotch. It courses posteriorly. Its insertion is on the base and muscular process of the arytenoid cartilage. It is innervated by the recurrent laryngeal nerve of the Cranial Nerve X (Vagus Nerve). Its function is to relax the vocal folds.

AUXILIARIES

The auxiliary muscles may not be the main muscles responsible for tasks such as adduction, abduction, tension, and relaxation, but these muscles aid the successful execution of these processes. The auxiliary laryngeal muscles are the superior thyroarytenoid, thyroepiglottic muscle, and the aryepiglottic muscle.

Superior Thyroarytenoid

The superior thyroarytenoid muscle originates from the inner angle of the thyroid cartilage. It courses posteriorly. Its insertion is on the muscular process of the arytenoid. It is innervated by the recurrent laryngeal nerve of the Cranial Nerve X (Vagus Nerve). It functions to relax the vocal folds.

Thyroepiglottic muscle

The thyroepiglottic muscle originates from the inner surface of the thyroid cartilage. It courses posteriorly-superiorly. Its insertion is on the lateral epiglottis. It is innervated by the recurrent laryngeal nerve of the Cranial Nerve X (Vagus Nerve). It functions to dilate the airway.

Aryepiglottic muscle

The aryepiglottic muscle originates from the continuation of the oblique arytenoid muscle from the arytenoid apex. It courses posteriorly-superiorly to the muscular component of the aryepiglottic fold. Its insertion is on the lateral epiglottis. It is innervated by the recurrent laryngeal nerve of the Cranial Nerve X (Vagus Nerve). It functions to constrict laryngeal opening.

SUMMARY

To sum everything up, take note of the following:

The muscular portion of the vocal folds is made up of the thyrovocalis and thyromuscularis muscles.
The cricothyroid muscle pulls the anterior cricoid and anterior thyroid together. This results to tension or stretching of the vocal folds.
The oblique arytenoid muscle aids the vocal folds in slip slightly inferiorly.
The transverse arytenoid muscle, along with the lateral cricoarytenoid muscle, is considered as the most effective adductor as its draws the posterior surface of two arytenoids closer together.
The posterior cricoarytenoid muscle abducts the vocal folds because of its location and the direction of its fibers.
The lateral cricoarytenoid muscle adducts the vocal folds by rocking the arytenoid medially.
The superior cricoarytenoid muscle serves as the sole relaxer among the laryngeal muscles. It relaxes the vocal folds.
The thyroepiglottis muscle is active in the pharyngeal stage in swallowing and keeps the epiglottis in its position. However, it does not have a significant function in speech production.

REFERENCES:

Bernes, S., & Jones, O. (2015). Muscles of the Larynx - Intrinsic - Extrinsic - TeachMeAnatomy. Teachmeanatomy.info. https://teachmeanatomy.info/neck/viscera/larynx/muscles/

IMAGE SOURCES:

https://www.researchgate.net/figure/The-aryepiglottis-oblique-arytenoid-transverse-arytenoid-muscles-and-the-posterior_fig1_341935532

https://www.kenhub.com/en/library/anatomy/oblique-arytenoid-muscle

https://www.kenhub.com/en/library/anatomy/lateral-cricoarytenoid-muscle

https://www.kenhub.com/en/library/anatomy/transverse-arytenoid-muscle

https://pin.it/5fKjDHe

Page updated

Report abuse