Geniohyoid
Neck · Head & Neck
The geniohyoid is a short, narrow suprahyoid muscle lying just above the mylohyoid, close to the midline in the floor of the mouth. It arises from the inferior genial tubercle, or mental spine, on the inner surface of the mandible and passes backward and slightly downward to insert on the anterior surface of the body of the hyoid bone. Its actions depend on which end is fixed: when the mandible is stable it elevates and draws the hyoid bone forward, and when the hyoid is fixed it helps depress the mandible, contributing to opening the mouth. Although it lies among muscles supplied by the trigeminal and facial nerves, the geniohyoid is instead innervated by fibres of the anterior ramus of the first cervical nerve (C1) that are carried along the hypoglossal nerve (CN XII).
Origin, Insertion, Action & Nerve
Origin
Inferior genial tubercle (mental spine) of the mandible
Insertion
Anterior surface of the body of the hyoid bone
Action
Elevates and draws the hyoid bone forward; depresses the mandible when the hyoid is fixed
Nerve
Anterior ramus of C1 carried by the hypoglossal nerve (CN XII)
Attachments explained
The Geniohyoid 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
Inferior genial tubercle (mental spine) of the mandible
Insertion
Anterior surface of the body of the hyoid bone
Action & function
When the Geniohyoid contracts, it produces the following movements: Elevates and draws the hyoid bone forward; depresses the mandible 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 Geniohyoid 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 Geniohyoid, impairing the movements it normally produces (elevates and draws the hyoid bone forward). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Geniohyoid (the OIANS method)
Fix the geniohyoid as the deepest and most central of the suprahyoid muscles, running from the mental spine of the mandible straight back to the hyoid. Because it forms a nearly horizontal strap between chin and hyoid, its dual action is easy to reason out: fix the jaw and it hauls the hyoid forward and up; fix the hyoid and it pulls the jaw down. Rehearsing both directions with one attachment held still keeps the two roles distinct.
The nerve is the memorable trap. Despite its position among trigeminal and facial muscles, the geniohyoid is driven by C1 fibres travelling with the hypoglossal nerve (CN XII), the same hitchhiking arrangement it shares with the thyrohyoid. Pairing geniohyoid and thyrohyoid together as the two C1-via-hypoglossal muscles is the cleanest way to remember this exception.
Frequently asked questions
Where is the Geniohyoid located?
The Geniohyoid is a muscle of the Neck group, located in the Head & Neck.
What is the origin of the Geniohyoid?
Inferior genial tubercle (mental spine) of the mandible
What is the insertion of the Geniohyoid?
Anterior surface of the body of the hyoid bone
What movements does the Geniohyoid produce?
Elevates and draws the hyoid bone forward; depresses the mandible when the hyoid is fixed
What nerve supplies the Geniohyoid?
Anterior ramus of C1 carried by the hypoglossal nerve (CN XII)
Is the Geniohyoid free to study in OIANS?
The Geniohyoid 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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