Anatomy

Origin

Superior head: lateral surface of greater wing of sphenoid. Inferior head: lateral surface of lateral pterygoid plate.

Insertion

Condyle of mandible, temporomandibular joint.

Nerve

Mandibular division of trigeminal nerve.

Actions

Opens jaw, protrudes mandible, moves mandible laterally for grinding teeth. It is the first muscle that activates when the mouth is opened. Superior head: active when mouth is closed and in swallowing. Inferior head: active when mouth is opened. The two heads act as antagonist muscles.