Intrinsic Muscles Associated With The Larynx
- Cricothyroid muscles lengthen and stretch the vocal folds.
- Posterior cricoarytenoid muscles abduct and externally rotate the arytenoid cartilages, resulting in abducted vocal folds.
- Lateral cricoarytenoid muscles adduct and internally rotate the arytenoid cartilages, which can result in adducted vocal folds.
- Transverse arytenoid muscle adducts the arytenoid cartilages, resulting in adducted vocal folds.
- Oblique arytenoid muscles narrow the laryngeal inlet by constricting the distance between the arytenoid cartilages.
- Vocalis muscles increase the thickness of the chords changing the tone.
- Thyroarytenoid muscles - sphincter of vestibule, narrowing the laryngeal inlet.
Notably, the only muscle capable of separating the vocal cords for normal breathing is the posterior cricoarytenoid. If this muscle is incapacitated on both sides, the inability to pull the vocal folds apart (abduct) will cause difficulty breathing. Bilateral injury to the recurrent laryngeal nerve would cause this condition. It is also worth noting that all muscles are innervated by the recurrent laryngeal branch of the vagus except the cricothyroid muscle, which is innervated by the external laryngeal branch of the superior laryngeal nerve (a branch of the vagus).
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