The four classical muscles of mastication elevate the

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

(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 In anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it is the ...

(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

, or lower jaw, is connected to the

temporal bone The temporal bone is a paired bone situated at the sides and base of the skull, lateral to the temporal lobe of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples where four of the cranial bone ...

of the skull via the

temporomandibular joint In anatomy, the temporomandibular joints (TMJ) are the two joints connecting the jawbone to the skull. It is a bilateral Synovial joint, synovial articulation between the temporal bone of the skull above and the condylar process of mandible be ...

. 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 The facial muscles are a group of striated skeletal muscles supplied by the facial nerve (cranial nerve VII) that, among other things, control facial expression. These muscles are also called mimetic muscles. They are only found in mammals, alth ...

, which are innervated by the

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of ta ...

(or CN VII), the muscles of mastication are innervated by the

trigeminal nerve In neuroanatomy, the trigeminal nerve (literal translation, lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for Sense, sensation in the face and motor functions ...

(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 pharyngeal arches, also known as visceral arches'','' are transient structures seen in the Animal embryonic development, embryonic development of humans and other vertebrates, that are recognisable precursors for many structures. In fish, t ...

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

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 help with the process, such as those of the tongue and the cheeks.

Clinical significance

* Temporomandibular joint disorder *

Bruxism Bruxism is excessive teeth grinding or jaw clenching. It is an oral Parafunctional habit, parafunctional activity; i.e., it is unrelated to normal function such as eating or talking. Bruxism is a common behavior; the global prevalence of brux ...

References

External links

* * http://www.med.umich.edu/lrc/coursepages/m1/anatomy2010/html/nervous_system/infratemp_lecture.html {{Authority control Muscles of the head and neck Chewing