Thyroarytenoid muscle

The thyroarytenoid muscle is a paired intrinsic muscle of the larynx that comprises of following sub-parts:

Sub-parts

1. External part

The external part refers to the broad flat part of the thyroarytenoid muscle which lies lateral to the fibro-elastic membrane of the larynx and the laryngeal ventricles and saccules.

• Origin: It originates from the inner surface of the thyroid cartilage near the angle and adjacent cricothyroid ligament.

• Insertion: The muscle fibres run posteriorly and slightly laterally to insert into the anterolateral surface of the arytenoid cartilage.

• Action: Its contraction draws the arytenoid cartilage forward toward the thyroid cartilage, thereby relaxing and shortening the vocal folds and lowering the pitch of the voice.

2. Thyroepiglottic part

• The thyroepiglottic part refers to the superior fibres of the thyroarytenoid muscle that continue upward towards the aryepiglottic fold. These fibres extend toward the lateral margin of the epiglottis, and also blend with the fibres of the aryepiglottic muscle.

• Action: Functionally, it assists in widening the laryngeal inlet by drawing the epiglottis and aryepiglottic folds laterally, particularly during respiration.

3. Vocalis muscle

The medial fibres of this thyroarytenoid muscle are often differentiated as the vocalis, which allows minute adjustments of vocal fold tension for precise modulation of pitch and tone.

Innervation

The thyroarytenoid is innervated by the recurrent laryngeal nerve, a branch of the vagus nerve (cranial nerve X).

Actions

By drawing the arytenoid cartilages anteriorly toward the thyroid cartilage, the thyroarytenoid muscle reduces tension on the vocal ligaments, producing a lower pitch during phonation. It also assists in narrowing the rima glottidis, contributing to fine control of voice and airway protection.

Paralysis of this muscle results in loss of vocal fold tension control, leading to a breathy or weak voice.