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, ...
, three muscles of mastication (''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
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 flo ...
, are responsible for opening the jaw in addition to the
lateral pterygoid.
Structure
The muscles are:
* The
masseter (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
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 teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
, 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. ...
of the skull via the
temporomandibular joint. 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, a ...
, which are innervated by the
facial nerve (or
CN VII), 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 che ...
(or
CN V). 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
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, a ...
, 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
*
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 gen ...
External links
*
* http://www.med.umich.edu/lrc/coursepages/m1/anatomy2010/html/nervous_system/infratemp_lecture.html
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Muscles of the head and neck