Thyrohyoid is a small, quadrilateral muscle found in the anterior triangle of the neck. It is one of four members of the group of muscles known as the infrahyoid muscles. The other three muscles in this group are sternohyoid, sternothyroid and omohyoid. The muscles are invested by the pretracheal layer of deep cervical fascia. They are separated into superficial and deep layers. Thyrohyoid occupies the deep layer with sternothyroid, while the other two are found in the superficial layer.
This article will discuss the anatomy and function of the thyrohyoid muscle.
|Origin||Oblique line of thyroid cartilage|
|Insertion||Inferior border of body and greater horn of hyoid bone|
Depresses hyoid bone
|Innervation||Anterior ramus of spinal nerve C1 via hypoglossal nerve (CN XII)|
|Blood supply||Branches of lingual and superior thyroid arteries|
Origin and insertion
Thyrohyoid is considered as a cranial extension of sternothyroid. It originates from the oblique line of the lamina of thyroid cartilage, where sternothyroid ends. The vertical fibers of the muscle continue cranially and converge (but do not meet) toward their insertion on the inferior border of the body and greater horn (cornu) of the hyoid bone.
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Thyrohyoid has several close relationships with surrounding structures in the anterior neck. It is crossed anteriorly by the oblique fibers of sternohyoid and the superior belly of omohyoid. Stylohyoid and the posterior belly of digastric pass the muscle superiorly.
The superior thyroid artery and vein (branch and tributary of the external carotid artery and internal jugular vein, respectively) are laterally related to the muscle. The lateral aspect of the thyrohyoid membrane is deep to the thyrohyoid muscle.
Thyrohyoid, unlike the other infrahyoid muscles, is not innervated by the ansa cervicalis. Instead, nerve fibers from the anterior rami of the first cervical spinal nerve (C1) reach the muscle via the hypoglossal nerve (CN XII). This nerve (often simply referred to as the nerve to thyrohyoid) branches from CN XII near the posterior border of hyoglossus.
The infrahyoid and superior laryngeal arteries are two branches of the superior thyroid artery that supplies the thyrohyoid muscle. Other unnamed branches of the lingual artery also contribute to the blood supply of this muscle.
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Thyrohyoid has two major functions. Firstly, it acts in conjunction with the other infrahyoid muscles and depresses the hyoid bone, which is helpful after swallowing has taken place. Secondly, when the hyoid bone is stabilized by the suprahyoid muscles, thyrohyoid elevates the larynx. This feature is important for vocalists who try to hit high notes.