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|Muscles of mastication|
|Mandibular division of the trifacial nerve.|
|Gray's||subject #109 385|
Mastication is accomplished through the activity of the four muscles of mastication.
- 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.
nose: procerus - nasalis (dilatator naris) - depressor septi nasi - levator labii superioris alaeque nasi
mastication: masseter - temporalis - pterygoid (lateral, medial)
tongue: extrinsic (genioglossus - hyoglossus - chondroglossus - styloglossus) intrinsic (superior longitudinal - inferior longitudinal - transversus - verticalis)
pharynx: pharyngeal constrictor (inferior, middle, superior) - stylopharyngeus - salpingopharyngeus
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