Muscles of mastication

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)
• The medial pterygoid
• The lateral pterygoid

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.

The muscles of facial expression, on the other hand, are derived from the second pharyngeal arch.