Cricothyroid muscle

Origin and insertion

This short muscle resides deep in the anterior neck, between the cricoid and thyroid cartilages of the larynx. It originates from the anterolateral part of the arch of the cricoid cartilage. The muscle fibers then separate to travel in two groups – oblique and straight. The inferiorly located oblique part travels posterolaterally to insert onto the inferior horn (cornu) of the thyroid cartilage. The straight part travels posterosuperiorly, taking a sharper incline than the fibers of the oblique part, to insert onto the inferior margin of the lamina of the thyroid cartilage. 

Relations

Each cricothyroid muscle has several important neighbors that serve as important landmarks for surgical planning. Firstly, it is separated from its contralateral fellow by a triangular space occupied by the cricothyroid ligament. This is an important area when establishing an emergency airway (discussed below). The muscle is caudal to the inferior border of the thyroid cartilage and medial to the cricothyroid joint. It travels superior to the lateral cricoarytenoid muscles but deep to the inferior constrictor muscle and its associated tendinous arch. The infrahyoid muscles are also located superficial to the cricothyroid muscle. 

The cricothyroid artery and the external branch of the superior laryngeal nerve approach the muscle from a superolateral angle as it travels toward the midline. The superior poles of the ipsilateral lobe and the pyramidal lobe (when present) of the thyroid gland also partially cover the cricothyroid muscles. 

We don’t want you to get rusty! Take some time and review key structures of the neck.

Innervation

The vagus nerve (CN X) provides motor innervation to the cricothyroid muscle by way of the external branch of the laryngeal nerve. It is the only member of the intrinsic muscles of the larynx that is not supplied by the recurrent laryngeal nerve.

Blood supply

Arterial supply to the cricothyroid muscle is from the cricothyroid artery. This artery arises from the superior thyroid artery, which is a branch of the external carotid artery. The cricothyroid artery crosses superiorly on the anterior cricothyroid ligament to meet with its contralateral counterpart.

A similarly named vein drains the cricothyroid muscle. It is a tributary of the superior thyroid vein, which drains to the internal jugular vein.

Functions

When the cricothyroid muscle contracts, it pulls the thyroid cartilage downward and anteriorly, causing rotation about the cricothyroid joint. This narrows the space between the thyroid and cricoid cartilages, and moves the thyroid cartilage away from the arytenoid cartilage. Consequently, there is stretching (lengthening), tightening and thinning of the vocal folds. Tighter, longer vocal folds produce higher-pitched sounds during vocalization.

If you want to learn the attachments, innervation and actions of muscles as efficiently as possible, check out Kenhub's muscle anatomy reference charts!