The four classical muscles of mastication elevate the mandible (closing the jaw) and move it forward/backward and laterally, facilitating biting and chewing. Other muscles are responsible for opening the jaw, namely the geniohyoid, mylohyoid, and digastric muscles (the lateral pterygoid may play a role).
Structure
The muscles are:
The masseter (composed of the superficial and deep head)
The temporalis (the sphenomandibularis is considered a part of the temporalis by some sources, and a distinct muscle by others)
In humans, the mandible, or lower jaw, is connected to the temporal bone of the skull via the temporomandibular joint. This is an extremely complex joint which permits movement in all planes. The muscles of mastication originate on the skull and insert into the mandible, thereby allowing for jaw movements during contraction.
Each of these primary muscles of mastication is paired, with each side of the mandible possessing one of the four.
Innervation
Unlike most of the other facial muscles, which are innervated by the facial nerve (or CN VII), the muscles of mastication are innervated by the trigeminal nerve (or CN V). More specifically, they are innervated by the mandibular branch, or V3. The mandibular nerve is both sensory and motor.
Development
Embryologically, the muscles of mastication are all derived from the first pharyngeal arch.
^ This article incorporates text available under the CC BY 4.0 license. Betts, J Gordon; Desaix, Peter; Johnson, Eddie; Johnson, Jody E; Korol, Oksana; Kruse, Dean; Poe, Brandon; Wise, James; Womble, Mark D; Young, Kelly A (June 28, 2023). Anatomy & Physiology. Houston: OpenStax CNX. 11.3 Axial muscles of the head, neck and back. ISBN978-1-947172-04-3.
