Anatomy

Origin

It arises in front from the lower half of the angle of the thyroid cartilage, and from the middle cricothyroid ligament.    

Nerve

Recurrent Laryngeal Nerve (Branch of the Vagus nerve, CN X).

Actions

The Thyreoarytœnoidei, consisting of two parts having different attachments and different directions, are rather complicated as regards their action.  Their main use is to draw the arytenoid cartilages forward toward the thyroid, and thus shorten and relax the vocal folds.  But, owing to the connection of the deeper portion with the vocal fold, this part, if acting separately, is supposed to modify its elasticity and tension, while the lateral portion rotates the arytenoid cartilage inward, and thus narrows the rima glottidis by bringing the two vocal folds together.