Digastric

Origin, Insertion, Action & Nerve

Attachments explained

The Digastric 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.

Action & function

When the Digastric contracts, it produces the following movements: Elevates hyoid bone; depresses mandible (opens jaw).

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 Digastric receives its nerve supply from the Anterior belly: mylohyoid nerve (CN V3); Posterior belly: facial nerve (CN VII).

Because a muscle can only contract when its nerve is intact, injury to the Anterior belly: mylohyoid nerve can weaken or paralyse the Digastric, impairing the movements it normally produces (elevates hyoid bone). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Digastric (the OIANS method)

Learn the digastric through its unusual double-bellied design: two muscle bellies slung to the hyoid bone by an intermediate tendon that runs through a fibrous loop. Because it links the mandible above to the hyoid below, it can either open the jaw when the hyoid is steadied or hoist the hyoid when the jaw is clenched, depending on which end is fixed.

The detail examiners love is the split nerve supply, which follows the muscle's mixed embryology. The anterior belly is driven by the trigeminal nerve through its mylohyoid branch (CN V3), while the posterior belly is driven by the facial nerve (CN VII). Pairing each belly with its arch of origin makes this two-nerve rule easy to reconstruct.

Frequently asked questions

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