The temporalis muscle is one of the four main muscles responsible for mastication, or chewing. Understanding the anatomy of this muscle is essential for comprehending how the lower jaw moves and functions. The specific points where the muscle begins and ends (origin and insertion) dictate its mechanical role in moving the jawbone. Knowledge of its anatomical attachments is foundational to understanding its function in closing and stabilizing the jaw.
Defining the Temporalis Muscle
The temporalis muscle is a broad, fan-shaped muscle situated on the side of the head. It is classified as one of the muscles of mastication, innervated by the trigeminal nerve, which work together to move the lower jaw. Its extensive shape allows it to generate significant force and control the jaw’s movements. The muscle fibers narrow into a stout tendon that must pass under the zygomatic arch (cheekbone) to reach the lower jaw.
The Precise Point of Insertion
The temporalis muscle inserts onto the coronoid process, a specific projection of the lower jawbone (mandible). The coronoid process is a thin, triangular prominence that juts upward from the front part of the mandibular ramus (the vertical portion of the jawbone). The muscle’s thick tendon travels deep to the zygomatic arch before attaching here. The attachment is not limited to the tip of the process, but extends across the medial surface and the anterior border of the structure.
The coronoid process acts like a lever for the muscle, allowing it to exert force on the jaw. The insertion point extends down the front edge of the ramus of the mandible, nearly reaching the area behind the last molar tooth. This extensive attachment ensures a wide distribution of force, allowing the muscle to perform both strong elevation and controlled retraction of the jaw.
Origin and Action of the Muscle
The temporalis muscle originates on the skull at the temporal fossa, a shallow depression on the side of the skull. This broad origin area includes parts of the frontal, parietal, temporal, and sphenoid bones, as well as the deep surface of the temporal fascia. The fan-like shape of the muscle results from these fibers converging toward the single, narrow insertion point on the mandible.
When the temporalis muscle contracts, its primary action is the elevation of the mandible, which closes the mouth. The vertically-oriented anterior and middle fibers are mainly responsible for this powerful closing action, generating a large portion of the biting force. The posterior fibers, which run more horizontally, are responsible for retracting the mandible (pulling the jaw backward). This combination of elevation and retraction makes the temporalis muscle a powerful stabilizer and mover during chewing.