There are four classical muscles of mastication. During

mastication Chewing or mastication is the process by which food is crushed and ground by teeth. It is the first step of digestion, and it increases the surface area of foods to allow a more efficient break down by enzymes. During the mastication process, th ...

, three muscles of mastication (''musculi masticatorii'') are responsible for

adduction Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...

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 The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical vertebra. ...

, such as the

mylohyoid muscle The mylohyoid muscle or diaphragma oris is a paired muscle of the neck. It runs from the mandible to the hyoid bone, forming the floor of the oral cavity of the mouth. It is named after its two attachments near the molar teeth. It forms the floor ...

, are responsible for opening the jaw in addition to the lateral pterygoid.

Structure

The muscles are: * The

masseter In human 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 ...

(composed of the superficial and deep head) * The

temporalis In anatomy, the temporalis muscle, also known as the temporal muscle, is one of the muscles of mastication (chewing). It is a broad, fan-shaped convergent muscle on each side of the head that fills the temporal fossa, superior to the zygomatic a ...

(the

sphenomandibularis The sphenomandibularis is a muscle attaching to the sphenoid bone and the mandible. It is a muscle of mastication. Unlike most of the muscles of the human body, which had been categorized several centuries ago, the sphenomandibularis was discov ...

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 In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

, or lower jaw, is connected to the

temporal bone The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples, and house the structures of the ears. Th ...

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 articulation between the temporal bone of the skull above and the mandible below; it is from these bones that it ...

. 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 tas ...

(or

CN VII 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 tas ...

), the muscles of mastication are innervated by the

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

(or

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

). More specifically, they are innervated by the mandibular branch, or V₃. The Mandibular nerve is both sensory and motor.

Development

This is a testament to their shared embryological origin from the first

pharyngeal arch The pharyngeal arches, also known as visceral arches'','' are structures seen in the embryonic development of vertebrates that are recognisable precursors for many structures. In fish, the arches are known as the branchial arches, or gill arch ...

. The

muscles of facial expression 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, al ...

, on the other hand, derive 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 are usually if not always helping the process, such as those of the tongue and the cheeks.

Clinical significance

Temporomandibular joint disorder Temporomandibular joint dysfunction (TMD, TMJD) is an umbrella term covering pain and dysfunction of the muscles of mastication (the muscles that move the jaw) and the temporomandibular joints (the joints which connect the mandible to the skull ...

Bruxism Bruxism is excessive teeth grinding or jaw clenching. It is an oral parafunctional activity; i.e., it is unrelated to normal function such as eating or talking. Bruxism is a common behavior; reports of prevalence range from 8% to 31% in the gene ...

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