Thyrohyoid
Neck · Head & Neck
The thyrohyoid is a short infrahyoid muscle that appears to continue the line of the sternothyroid, running from the oblique line of the thyroid cartilage upward to the inferior border of the body and the greater horn of the hyoid bone. Because it links the thyroid cartilage to the hyoid, its action depends on which is held fixed: it can depress the hyoid bone toward the larynx, or, when the hyoid is steadied by the suprahyoid muscles, it elevates the larynx, drawing the thyroid cartilage up toward the hyoid. Unlike the other strap muscles supplied by the ansa cervicalis, the thyrohyoid is innervated by fibres of the anterior ramus of C1 that travel with the hypoglossal nerve (CN XII).
Origin, Insertion, Action & Nerve
Origin
Oblique line of the thyroid cartilage
Insertion
Inferior border of the body and greater horn of the hyoid bone
Action
Depresses the hyoid bone; elevates the larynx when the hyoid is fixed
Nerve
Anterior ramus of C1 carried by the hypoglossal nerve (CN XII)
Attachments explained
The Thyrohyoid is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Oblique line of the thyroid cartilage
Insertion
Inferior border of the body and greater horn of the hyoid bone
Action & function
When the Thyrohyoid contracts, it produces the following movements: Depresses the hyoid bone; elevates the larynx when the hyoid is fixed.
As part of the Neck group of the Head & Neck, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Thyrohyoid receives its nerve supply from the Anterior ramus of C1 carried by the hypoglossal nerve (CN XII). This nerve carries fibres from spinal segment(s) C1.
Because a muscle can only contract when its nerve is intact, injury to the Anterior ramus of C1 carried by the hypoglossal nerve or to its spinal roots (C1) can weaken or paralyse the Thyrohyoid, impairing the movements it normally produces (depresses the hyoid bone). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Thyrohyoid (the OIANS method)
See the thyrohyoid as the short final segment of the sternothyroid, carrying the line from the thyroid cartilage up onto the hyoid bone. This makes its two actions logical: with the hyoid loose it pulls the hyoid down, and with the hyoid fixed it lifts the larynx, a movement important in high-pitched phonation and swallowing. Reasoning from which end is anchored keeps the pair of actions straight.
The thyrohyoid shares the geniohyoid's exceptional supply: C1 fibres carried by the hypoglossal nerve (CN XII), not the ansa cervicalis. Remembering geniohyoid and thyrohyoid together as the two neck muscles that borrow the hypoglossal nerve is the surest way to avoid grouping the thyrohyoid with the ansa-supplied straps around it.
Frequently asked questions
Where is the Thyrohyoid located?
The Thyrohyoid is a muscle of the Neck group, located in the Head & Neck.
What is the origin of the Thyrohyoid?
Oblique line of the thyroid cartilage
What is the insertion of the Thyrohyoid?
Inferior border of the body and greater horn of the hyoid bone
What movements does the Thyrohyoid produce?
Depresses the hyoid bone; elevates the larynx when the hyoid is fixed
What nerve supplies the Thyrohyoid?
Anterior ramus of C1 carried by the hypoglossal nerve (CN XII)
Is the Thyrohyoid free to study in OIANS?
The Thyrohyoid is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Head & Neck is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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