In human anatomy, the masseter is one of the muscles of mastication
. Found only in mammals, it is particularly powerful in
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpa ...
to facilitate chewing of plant matter.
The most obvious muscle of mastication is the masseter muscle, since it is the most superficial and one of the strongest.
The masseter is a thick, somewhat quadrilateral muscle, consisting of three heads, superficial, deep and coronoid. The fibers of superficial and deep heads are continuous at their insertion.
The superficial head, the larger, arises by a thick, tendinous
An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join muscl ...
from the temporal process of the zygomatic bone
, and from the anterior two-thirds of the inferior border of the zygomatic arch
. Its fibers pass inferior and posterior, to be inserted into the angle of the mandible and inferior half of the lateral surface of the ramus of the mandible
The deep head is much smaller, and more muscular in texture. It arises from the posterior third of the lower border and from the whole of the medial surface of the zygomatic arch. Its fibers pass downward and forward, to be inserted into the upper half of the ramus as high as the
coronoid process of the mandible
In human anatomy, the mandible's coronoid process (from Greek ''korōnē'', denoting something hooked) is a thin, triangular eminence, which is flattened from side to side and varies in shape and size. Its anterior border is convex and is continuou ...
. The deep head of the muscle is partly concealed, anteriorly, by the superficial portion. Posteriorly, it is covered by the parotid gland
The coronoid head of the masseter's tendon and muscle fibers run posterolaterally from the coronoid process of the mandible towards the posterior third of the zygomatic arch. Its function is believed to be the retraction of the mandible and the stabilization of the mandibular coronoid process.
Along with the other three muscles of mastication
, medial pterygoid
, and lateral pterygoid
), the masseter is innervated by the anterior division of the mandibular division (V3)
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 chew ...
. The innervation pathway is:
gyrus precentralis > genu capsula interna > nucleus motorius nervi trigemini > nervus trigeminus > nervus mandibularis > musculus masseter.
The action of the muscle during bilateral contraction of the entire muscle is to elevate the mandible, raising the lower jaw. Elevation of the mandible occurs during the closing of the jaws. The masseter parallels the
medial pterygoid muscle
The medial pterygoid muscle (or internal pterygoid muscle), is a thick, quadrilateral muscle of the face. It is supplied by the mandibular branch of the trigeminal nerve (V). It is important in mastication (chewing).
The medial ptery ...
, but it is stronger and superficial fibres can cause protrusion.
To perform an extraoral examination, stand near the patient and visually inspect and bilaterally palpate the muscle. Place the fingers of each hand over the muscle and ask the patient to clench his or her teeth several times.
The masseter muscle can become enlarged in patients who habitually clench or grind (with
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 ...
) their teeth and even in those who constantly chew gum. This masseteric
Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J. ...
is asymptomatic and soft; it is usually bilateral but can be unilateral. Even if the hypertrophy is bilateral, asymmetry of the face may still occur due to unequal enlargement of the muscles. This extraoral enlargement may be confused with parotid salivary gland disease, dental infections, and maxillofacial neoplasms. However, no other signs are present except those involved in changes in occlusion intraorally such as pain, and the enlargement corresponds with the outline of the muscle. Most patients seek medical attention because of comments about facial appearance, and this situation may be associated with further pathology of the temporomandibular joint
[Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, p. 97]
Finally, the muscle undergoes spasm with
Malignant hyperthermia (MH) is a type of severe reaction that occurs in response to particular medications used during general anesthesia, among those who are susceptible. Symptoms include muscle rigidity, fever, and a fast heart rate. Complicati ...
as do other
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...
, but this one is easily noted, since it is on the face.
Singing is the act of creating musical sounds with the voice. A person who sings is called a singer, artist or vocalist (in jazz and/or popular music). Singers perform music (arias, recitatives, songs, etc.) that can be sung with or wit ...
often experience various kinds of masseter tension, which is often treated with transdermal massages or stretches as a vocal warm-up
In other animals
The masseter muscle's positioning is a distinguishing feature of hystricognathous
creatures such as mole-rats
, where it passes partially through the
In human anatomy, the infraorbital foramen is one of two small holes in the skull's upper jawbone ( maxillary bone), located below the eye socket and to the left and right of the nose. Both holes are used for blood vessels and nerves. In anatomic ...
and connects to the bone on the opposite side.
File:Illu_head_neck_muscle.jpg, Muscles of the head and neck.
File: Gray1024.png, Dissection, showing salivary glands of right side (Masseter visible at center)
File:Gray137.png, Left temporal bone, outer surface
File:Gray141.png, Left temporal bone, inferior surface
File:Gray166.png, Left zygomatic bone, temporal surface
File:Gray176.png, Mandible, outer surface, side view
File:Gray508.png, The arteries of the face and scalp.
File:Gray557.png, Veins of the head and neck.
File:Gray781.png, Mandibular division of the trifacial nerve.
File:Slide10por.JPG, Masseter muscle. Deep dissection. Mummification process.
* Zygomasseteric system
Muscles of the head and neck