The Four Primary Muscles That Move the Jaw

Four muscles of mastication—masseter, temporalis, medial pterygoid, and lateral pterygoid—are responsible for the major movements of the mandible at the TMJ. All derive embryologically from the first pharyngeal arch and are innervated by the mandibular division of the trigeminal nerve.

The masseter and temporalis are powerful elevators that close the mouth. The temporalis also contributes to retraction through its posterior fibers. The medial pterygoid assists in elevation and helps produce lateral movements when acting unilaterally.

The lateral pterygoid is unique: its inferior head helps depress and protrude the mandible, while its superior head attaches to the articular disc and capsule, coordinating disc movement with condylar translation. Bilateral contraction of the lateral pterygoids produces protrusion; unilateral action shifts the jaw toward the opposite side.

These muscles work in finely tuned pairs, allowing the wide range of motions required for speech and mastication while maintaining the precise relationship between the two TMJs.

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