Muscles of mastication

During mastication, four muscles of mastication are responsible for adduction and lateral motion of the jaw. Other muscles, usually associated with the hyoid such as the sternohyomastoid, are responsible for opening the jaw.

Muscles

• The masseter
• 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

Each of these primary muscles of mastication is paired, with each side of the mandible possessing one of the four.

Innervation and embryological origin

Unlike most of the other facial muscles, which are innervated by the facial nerve (or CN VII), the muscles of mastication are all innervated by the trigeminal nerve (or CN V). More specifically, they are innervated by the mandibular branch, or V₃. This is a testament to their shared embryological origin from the first branchial arch.

The muscles of facial expression, on the other hand, derive from the second branchial arch.

Origin and insertion

In humans, the mandible, or lower jaw, is connected to the temporal bone of the skull via the temporomandibular joint, 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.

Function

The mandible is the only bone that moves during mastication and other activities, such as talking.

While these four muscles are the primary participants in mastication, other muscles are usually if not always helping the process, such as those of the tongue and the cheeks.

External links

• MeSH Masticatory+Muscles
• http://anatomy.med.umich.edu/head/infratemp_lecture.html