Thyrohyoid muscle: origin, insertion, action and innervation

The thyrohyoid is a small, four-sided muscle that links the thyroid cartilage of the larynx to the hyoid bone just above it. It either pulls the hyoid down or, when the hyoid is held still, lifts the larynx, and its nerve is a branch of C1 that travels with the hypoglossal nerve.

Where it is

The thyrohyoid sits on the side of the upper larynx, under the sternohyoid and the superior belly of the omohyoid. It is the shortest of the four infrahyoid muscles.

It looks like an upward continuation of the sternothyroid: both use the same oblique line on the thyroid cartilage, one going down to the sternum and the other going up to the hyoid.

Deep to the thyrohyoid lies the thyrohyoid membrane, the sheet that fills the gap between the hyoid and the top of the larynx. The internal laryngeal nerve and the superior laryngeal artery pierce this membrane under cover of the muscle on their way into the larynx.

Origin and insertion

• Origin: the oblique line of the thyroid cartilage, the diagonal ridge on the outer surface of each plate.
• Insertion: the lower border of the greater horn of the hyoid bone and the adjoining part of its body.

The fibers run straight up, so the muscle is a short, flat rectangle spanning the narrow gap between the thyroid cartilage and the hyoid.

What it does

The thyrohyoid has two actions, and which one you see depends on which end is held still:

1. Depresses the hyoid: when the larynx is fixed by the sternothyroid below, the thyrohyoid pulls the hyoid down toward the thyroid cartilage.
2. Elevates the larynx: when the hyoid is fixed by the suprahyoid muscles above, the thyrohyoid pulls the thyroid cartilage up. This helps raise the larynx during swallowing.

That second action makes it the only infrahyoid muscle that helps lift the larynx.

Innervation and blood supply

The thyrohyoid is the odd one out among the strap muscles. It is not supplied by the ansa cervicalis but by the nerve to thyrohyoid. This nerve carries fibers from the first cervical nerve (C1) that have joined the hypoglossal nerve (CN XII) for part of their journey, then leave it near the greater horn of the hyoid.

The hypoglossal nerve only gives these fibers a ride: the motor supply is cervical, not cranial.

Blood comes from the superior thyroid artery and its superior laryngeal branch, which passes just under the muscle.

How to remember it

• Thyroid to hyoid, short hop: the thyrohyoid covers the smallest distance of all the strap muscles.
• The hitchhiker nerve: C1 fibers hitch a ride on the hypoglossal nerve to reach the thyrohyoid (and the geniohyoid).
• Odd one out: "three straps on the ansa, one on twelve's ride". Sternohyoid, sternothyroid and omohyoid use the ansa cervicalis; the thyrohyoid does not.
• Two-way muscle: fix the top and it lifts the larynx; fix the bottom and it lowers the hyoid.

Test yourself in the neck quiz.

Frequently asked questions

What does the thyrohyoid muscle do?

It depresses the hyoid bone, and when the hyoid is fixed it elevates the larynx.

What nerve supplies the thyrohyoid?

The nerve to thyrohyoid, made of C1 fibers that travel with the hypoglossal nerve (CN XII).

Is the thyrohyoid supplied by the hypoglossal nerve?

Not really. The fibers run inside the hypoglossal nerve for a while, but they come from C1, a cervical spinal nerve.

What lies deep to the thyrohyoid?

The thyrohyoid membrane, pierced by the internal laryngeal nerve and the superior laryngeal artery.

Sources

• OpenStax, Anatomy and Physiology 2e, 11.3 Axial muscles of the head, neck and back
• OpenStax, Anatomy and Physiology 2e, 22.1 Organs and structures of the respiratory system
• Z-Anatomy, the libre 3D atlas of anatomy