External part of thyro-arytenoid muscle

At a glance

English

External part of thyro-arytenoid muscle

Latin (TA2)

Pars externa musculi thyreoarytenoidei

System

Muscle

Region

Neck

Side

Paired, left and right

About the external part of thyro-arytenoid muscle

Thyro-arytenoid is a broad, thin intrinsic muscle of the larynx lying in the side wall of the glottis, lateral to the vocal fold. It is usually divided into three regions. Its deepest, medial fibres next to the vocal ligament form vocalis; a small slip running up to the epiglottis forms the thyro-epiglottic part; and the remaining bulk of the muscle, lateral to vocalis, is the external part described here.

The fibres arise in front from the inner surface of the thyroid cartilage near the midline angle, low down, and from the adjacent cricothyroid ligament. They run backwards and slightly outwards, lateral to the vocal fold and the conus elasticus, to the front and side of the arytenoid cartilage, including its anterolateral surface and muscular process. Some upper fibres curve up into the ary-epiglottic fold, and some lie in the wall of the laryngeal ventricle.

Because the fibres run from front to back beside the glottis, contraction draws the arytenoid cartilages forwards towards the thyroid. This shortens and slackens the vocal folds, lowering the pitch of the voice, and it also turns the arytenoids slightly inwards so that the folds come together. The external part thus helps close the glottis and assists the lateral crico-arytenoid. Fibres reaching the ventricle and the ary-epiglottic fold can narrow the vestibule and help seal the airway during swallowing.

Like all intrinsic laryngeal muscles except cricothyroid, it is supplied by the recurrent laryngeal nerve, a branch of the vagus, and its blood comes from the laryngeal branches of the superior and inferior thyroid arteries. Injury to the recurrent laryngeal nerve, for instance during thyroid surgery, weakens this muscle along with its neighbours, giving a breathy, weak voice.

Attachments, action and supply

Origin

Inner surface of the thyroid cartilage near its angle and the adjacent cricothyroid ligament.

Insertion

Anterolateral surface and muscular process of the arytenoid cartilage.

Action

Draws the arytenoids forwards, shortening and relaxing the vocal folds; helps close the glottis.

Nerve supply

Recurrent laryngeal nerve (from the vagus, CN X).

Blood supply

Laryngeal branches of the superior and inferior thyroid arteries.