Muscles of the larynx

Which one of the following options is a TRUE statement regarding the intrinsic muscles of the larynx?

a) The cricothyroids are the only muscles to tense the cords

b) The posterior cricoarytenoids, supplied by the recurrent laryngeal nerve, adduct the

cords

c) Vocalis is supplied by the recurrent laryngeal nerve but is not considered an

intrinsic muscle of the larynx

d) Thyrohyoid elevates the larynx

e) The internal laryngeal nerve supplies only one of these muscles

Answer: a

Explanation

There are six intrinsic muscles of the larynx (although they may be paired or subdivided).

The first five are supplied by the recurrent laryngeal nerve, which is a branch of

the tenth cranial nerve (the vagus): posterior cricoarytenoid, lateral cricoarytenoid,

transverse arytenoid, thyroarytenoid and vocalis (of thyroarytenoid). The sixth intrinsic

muscle is the cricothyroid and is supplied by the external laryngeal nerve, which is a

branch of the superior laryngeal nerve, another branch of the vagus. The superior

laryngeal nerve also branches to the internal laryngeal nerve, which supplies sensation

to the laryngeal mucosa above the cords including the underside of the epiglottis.

Above this, including the vallecula, sensation is from the glossopharyngeal nerve.

Sensation below the cords is supplied by the recurrent laryngeal nerve. In terms of

the action of each of the intrinsic muscles, they are as follows: posterior cricoarytenoid –

abducts cords; lateral cricoarytenoid – adducts cords; transverse arytenoids – adducts

cords; thyroarytenoids – relaxes cords; vocalis – adjusts cords; cricothyroid – tenses

cords.

Sternohyoid (depresses larynx), thyrohyoid (elevates larynx) and the posterior

constrictor of the pharynx are extrinsic muscles of the larynx.