Oblique arytenoid muscle

Origin and insertion

Oblique arytenoid originates from the posterior aspect of the muscular process of arytenoid cartilage. The muscle extends obliquely towards its superiorly located insertion; the superior pole of the contralateral arytenoid cartilage. Along its path, the oblique arytenoid muscle crosses its pair from the opposite side, forming the letter “X”.

Relations

There are two arytenoid muscles located on the posterior aspect of the larynx; oblique arytenoid and transverse arytenoid, with oblique arytenoid being the more superficial of the two. Some authors consider the transverse and oblique arytenoids to be two parts of the same muscle, calling them the arytenoid or interarytenoid muscle. 

Upon inserting at the apex of the contralateral arytenoid cartilage, certain fibers of the oblique arytenoid muscle continue around the arytenoid apex and are prolonged into the aryepiglottic fold, forming the aryepiglottic muscle.

Innervation

Oblique arytenoid is innervated by the recurrent laryngeal nerve, a branch of the vagus nerve (CN X). 

Blood supply

The oblique arytenoid muscle receives its arterial supply from the laryngeal branches of the superior and inferior thyroid artery; branches of the external carotid artery and the thyrocervical trunk, respectively. Venous blood from the oblique arytenoid muscle is drained into the superior and inferior laryngeal veins, which are tributaries of the internal jugular vein. 

Function

The oblique arytenoid muscle acts to adduct the arytenoid cartilages, bring the arytenoid cartilages closer to the tubercule of epiglottis and it also, through its extended fibers, adducts the aryepiglottic folds. Thus, this muscle functions to adduct the vocal folds, close the posterior portion of rima glottidis and narrow the laryngeal inlet.

When acting in combination with transverse arytenoid and aryepiglottic, it acts as a sphincter of the laryngeal inlet. This reflexive action results in a closing of the rima glottidis which is a protective mechanism that prevents aspiration during swallowing or coughing.

When the oblique arytenoid acts together with other vocal fold adductors (transverse arytenoid, lateral cricoarytenoid, thyroarytenoid) and vocal fold tensors (cricothyroid, thyroarytenoid, vocalis), the vocal folds are approximated (adductive tension) and the rima glottis is closed. Expired air is pushed through the narrowed rima glottidis which causes vibrations of the tensed vocal ligaments and produces phonation.

In contrast, when the vocal cords are adducted but the oblique and transverse arytenoid muscles are relaxed, the arytenoid cartilages are spaced out, and thus air passing through the rima glottidis does not cause significant vibration of the vocal cords. This is the mechanism behind whispering, where breathing is modified into voice with the absence of tone.