The temporalis muscle is a significant structure located on the side of the head, recognized as one of the primary muscles responsible for controlling the lower jaw. It plays an important role in the mechanics of chewing and biting. Understanding this muscle involves tracing its path from its broad attachment on the skull to its final point on the jawbone. This anatomical structure generates the force needed for mandibular movements.
Anatomy of the Temporalis Muscle
The temporalis muscle is distinguished by its broad, fan-shaped structure, covering a large area of the side of the skull. It occupies the temporal fossa, a shallow depression formed by parts of the temporal, parietal, frontal, and sphenoid bones. It is classified as the largest of the four muscles of mastication dedicated to the movement of the mandible.
The muscle’s fibers run downward and converge as they descend toward the lower jaw, passing deep to a prominent bony arch. The muscle is covered by a dense, fibrous sheath known as the temporal fascia, which contributes to its structural integrity.
Defining the Origin
The temporalis muscle begins with a broad attachment site known as the origin, spanning a considerable portion of the skull. The muscle originates from the entire surface of the temporal fossa, an area situated below the inferior temporal line. This extensive bony surface provides the foundation for the muscle’s wide, fan-like shape.
Muscle fibers also arise from the deep surface of the temporal fascia, the strong connective tissue covering the muscle. As the fibers descend from this extensive origin, they narrow and converge. The anterior fibers run vertically, while the posterior fibers are oriented horizontally, contributing to the muscle’s varied functional roles.
The Insertion Point
The insertion of the temporalis muscle is its movable attachment, located precisely on the mandible, or lower jawbone. The muscle fibers condense into a strong, thick tendon that must pass deep to the zygomatic arch, the prominent bony arch forming the cheekbone. This passage directs the force generated by the muscle to the lower jaw.
The primary insertion site is the coronoid process of the mandible, a sharp projection found at the top of the jaw’s vertical portion, the ramus. The tendon attaches not only to the tip of this process but also extends down along its medial surface. This provides a secure and expansive attachment for the muscle’s powerful tendon.
The insertion continues onto the anterior border of the mandibular ramus, extending downward almost to the level of the last molar tooth. This extensive attachment area allows the contractile force from the broad origin to be concentrated onto the jawbone.
Action of the Temporalis Muscle
The mechanical action of the temporalis muscle is directly related to its attachment points on the skull and the movable jawbone. The primary function is the elevation of the mandible, which is the action of closing the mouth and bringing the teeth together during biting. This powerful upward movement is achieved by the contraction of all the muscle’s fibers.
The temporalis muscle also performs a secondary action known as retraction. This movement pulls the mandible backward, helping to position the jaw correctly within the temporomandibular joint. The posterior, horizontally aligned fibers are mainly responsible for this retraction. The coordinated elevation and retraction make the temporalis efficient for both forceful biting and precise jaw positioning.