Muscles of mastication
|Muscles of mastication|
|Mandibular division of the trigeminal nerve.|
|Gray's||subject #109 385|
There are four classical muscles of mastication. During mastication, three muscles of mastication (or musculi masticatorii) are responsible for adduction of the jaw, and one (the lateral pterygoid) helps to abduct it. All four move the jaw laterally. Other muscles, usually associated with the hyoid such as the sternohyomastoid, are responsible for opening the jaw in addition to the lateral pterygoid.
- 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.
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.
- Masticatory Muscles at the US National Library of Medicine Medical Subject Headings (MeSH)