Cricothyroid muscle

The cricothyroid muscle is a paired, fan-shaped intrinsic muscle of the larynx that lies on the anterolateral surface of the cricoid cartilage. It serves as the primary tensor of the vocal folds, playing a key role in the modulation of pitch during phonation.

Origin

The cricothyroid muscle arises from the anterolateral surface of the cricoid cartilage

Insertion

The muscle fibres ascends obliquely to insert into the inferior margin and inferior horn of the thyroid cartilage. It is divided into two parts: an oblique part (pars obliqua), which runs upward and outward, and a straight part (pars recta), which runs vertically.

Innervation and action

The cricothyroid muscle is supplied by the external branch of the superior laryngeal nerve (a branch of the vagus nerve, CN X) — the only intrinsic laryngeal muscle not innervated by the recurrent laryngeal nerve.

By tilting the thyroid cartilage forward and downward at the cricothyroid joint, it stretches and tenses the vocal folds, thereby raising the pitch of the voice. Relaxation of the muscle allows the vocal folds to shorten and slacken, lowering the pitch.

Clinical correlate

Clinically, injury to the external laryngeal nerve (e.g., during thyroid surgery) can paralyze the cricothyroid, resulting in loss of ability to produce high-pitched sounds and a monotonous voice quality.