The primary muscles of mastication include four paired muscles that primarily act during eating and produce movements at the temporomandibular joints (TMJs), enabling such functions as chewing. Each person has the following primary muscles of mastication:

All these muscles mentioned above close the mouth by elevating the mandible, except for the lateral pterygoid. It opens the mouth by depressing and moving the mandible forward. Overall, these muscles originate from the bones of the skull and insert onto the posterior half of the mandible. The mandibular ramus, mandibular angle, condylar and coronoid processes are extensively clothed in muscle insertion sites.

All primary muscles have a common innervation source. They all receive innervation from the branches of the mandibular division (CN V3) of the trigeminal nerve (CN V). And finally, another shared feature of the masticatory muscles is that they are supplied by the branches of the maxillary artery.

Overall, the primary muscles of mastication provide the following functions:

Elevation of the mandible - they close the mouth by elevating the lower jaw;
Depression of the mandible - these muscles open the mouth by depressing the lower jaw;
Protrusion of the mandible - they move the mandible forward;
Retraction of the mandible - these muscles pull the mandible backward;
Side-to-side movements (rotation) of the mandible - they move the mandible to each side of the head.

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Primary muscles of mastication