Masticatory Muscles: Anatomy and Jaw Movement Functions

Masticatory muscles share a common characteristic: they are all inserted at the base of the skull and upper jaw, serving the primary purpose of moving the jaw.

Temporal Muscle

This muscle occupies the temporal fossa. It is inserted above the level of the temporal line and the entire fossa. Its fibers are directed downward and converge, ending in a tendon at the level of the coronoid process of the maxilla. Innervation is provided by the temporal nerve, a branch of the mandibular nerve. Its action is to elevate the jaw, attaching it to the upper jaw.

Masseter Muscle

A short, thick muscle with a quadrilateral shape, the masseter is located on the outer face of the ramus of the mandible. Its upper insertion is at the zygomatic arch, and its descending fibers follow a path ending at the posterior angle of the jaw. Innervation is by a branch of the mandibular nerve. Its action is the same as the temporal muscle: to elevate the jaw.

Pterygoid Muscles

There are two pterygoid muscles, often referred to as the medial and lateral pterygoids.

Medial Pterygoid

This muscle has a quadrilateral shape, extending from the pterygoid plate to the posterior angle of the jaw. One of its attachments is the pterygoid fossa. It is located behind the lower jaw. Its fibers are directed outward to terminate at the rear inner corner of the jaw. The nerve supply comes from a branch of the mandibular nerve. Apart from raising the mandible, the oblique direction of its fibers contributes to lateral jaw movements. It elevates the mandible.

Lateral Pterygoid

This muscle is situated externally, housed within the infratemporal fossa. It originates at the base of the skull, with two distinct origins for its two fascicles. From these dual internal insertions, its fibers are directed outward to terminate on the inner side at the level of the temporomandibular joint. Innervation is by a branch of the mandibular nerve. Acting with the base of the skull as a fixed point, its contraction produces an external joint movement at the condyle. If both lateral pterygoid muscles contract simultaneously, the condyles move forward, causing the upper dental arch to protrude beyond the lower (mandibular prognathism). If only one contracts, it retracts the condyle with a rotating motion, causing the chin to move to the opposite side of the contracting muscle. Alternate contraction moves the chin side-to-side, sliding the upper molars against the lower, which aids in crushing food. It elevates the jaw.