Masseter muscle

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Masseter
Gray378 (masseter highlight).png
The left masseter muscle (red highlight), partially covered by superficial muscles such as the platysma muscle (below) and both the zygomaticus major and minor muscles
Details
Origin Zygomatic arch and maxillary process of zygomatic bone
Insertion Angle surface of ramus of mandible, coronoid process
Artery Masseteric artery
Nerve Mandibular nerve (V3)
Actions Elevation (as in closing of the mouth) and protrusion of mandible
Identifiers
Latin musculas masseter
MeSH D008406
TA98 A04.1.04.002
TA2 2105
FMA 48996
Anatomical terms of muscle

In anatomy, the masseter [help 1] is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. [5] The most obvious muscle of mastication is the masseter muscle, since it is the most superficial and one of the strongest.

Contents

Structure

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.

Superficial head

The superficial head, the larger, arises by a thick, tendinous aponeurosis from the zygomatic process of the maxilla, 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.

Deep head

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. The deep head of the muscle is partly concealed, anteriorly, by the superficial portion. Posteriorly, it is covered by the parotid gland.

Coronoid head

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. [6] [7]

Innervation

Along with the other three muscles of mastication (temporalis, medial pterygoid, and lateral pterygoid), the masseter is innervated by the anterior division of the mandibular division (V3) of the trigeminal nerve. The innervation pathway is: gyrus precentralis > genu capsula interna > nucleus motorius nervi trigemini > nervus trigeminus > nervus mandibularis > musculus masseter.

Function

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, but it is stronger and superficial fibres can cause protrusion.

Clinical significance

Examination

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. [8]

Pathology

The masseter muscle can become enlarged in patients who habitually clench or grind (with bruxism) their teeth and even in those who constantly chew gum. This masseteric hypertrophy 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. [8]

Finally, the muscle undergoes spasm with malignant hyperthermia as do other skeletal muscles, but this one is easily noted, since it is on the face.

Singers often experience various kinds of masseter tension, which is often treated with transdermal massages or stretches as a vocal warm-up. [9] [10]

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 infraorbital foramen and connects to the bone on the opposite side.

In toothed whales, the masseter muscle, made redundant due to a shift in ingesting food from chewing to swallowing, provides the tissue for acoustic fat bodies, including the melon, used for echolocation. [11]

Additional images

See also

Notes

  1. ↑ The word masseter (usually /məˈsiːtər/ , [1] [2] [3] sometimes /ˈmæsɪtər/ [4] ) comes through Neo-Latin from Greek μασᾶσθαι masasthai, "to chew".

Related Research Articles

<span class="mw-page-title-main">Temporomandibular joint</span> Joints connecting the jawbone to the skull

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 its name is derived. The joints are unique in their bilateral function, being connected via the mandible.

Articles related to anatomy include:

<span class="mw-page-title-main">Mandibular nerve</span> Branch of the trigeminal nerve responsible for the lower face and jaw

In neuroanatomy, the mandibular nerve (V3) is the largest of the three divisions of the trigeminal nerve, the fifth cranial nerve (CN V). Unlike the other divisions of the trigeminal nerve (ophthalmic nerve, maxillary nerve) which contain only afferent fibers, the mandibular nerve contains both afferent and efferent fibers. These nerve fibers innervate structures of the lower jaw and face, such as the tongue, lower lip, and chin. The mandibular nerve also innervates the muscles of mastication.

<span class="mw-page-title-main">Parotid gland</span> Major salivary gland in many animals

The parotid gland is a major salivary gland in many animals. In humans, the two parotid glands are present on either side of the mouth and in front of both ears. They are the largest of the salivary glands. Each parotid is wrapped around the mandibular ramus, and secretes serous saliva through the parotid duct into the mouth, to facilitate mastication and swallowing and to begin the digestion of starches. There are also two other types of salivary glands; they are submandibular and sublingual glands. Sometimes accessory parotid glands are found close to the main parotid glands.

<span class="mw-page-title-main">Temporalis muscle</span> Muscle on the side of the head which aids in chewing

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 arch so it covers much of the temporal bone.Temporal refers to the head's temples.

<span class="mw-page-title-main">Muscles of mastication</span> Muscles that aid chewing

The four classical muscles of mastication elevate the mandible 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.

<span class="mw-page-title-main">Medial pterygoid muscle</span> Muscle involved in chewing

The medial 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).

<span class="mw-page-title-main">Lateral pterygoid muscle</span> Muscle of mastication

The lateral pterygoid muscle (or external pterygoid muscle) is a muscle of mastication. It has two heads. It lies superior to the medial pterygoid muscle. It is supplied by pterygoid branches of the maxillary artery, and the lateral pterygoid nerve (from the mandibular nerve, CN V3). It depresses and protrudes the mandible. When each muscle works independently, they can move the mandible side to side.

<span class="mw-page-title-main">Stylomandibular ligament</span> Ligament between the jaw bone and the skull

The stylomandibular ligament is the thickened posterior portion of the investing cervical fascia around the neck. It extends from near the apex of the styloid process of the temporal bone to the angle and posterior border of the angle of the mandible, between the masseter muscle and medial pterygoid muscle. The stylomandibular ligament limits mandibular movements, such as preventing excessive opening.

<span class="mw-page-title-main">Condyloid process</span>

The condyloid process or condylar process is the process on the human and other mammalian species' mandibles that ends in a condyle, the mandibular condyle. It is thicker than the coronoid process of the mandible and consists of two portions: the condyle and the constricted portion which supports it, the neck.

<span class="mw-page-title-main">Pterygoid processes of the sphenoid</span> Bone plates projecting from the sphenoid bone of the skull

The pterygoid processes of the sphenoid, one on either side, descend perpendicularly from the regions where the body and the greater wings of the sphenoid bone unite.

<span class="mw-page-title-main">Greater wing of sphenoid bone</span> Large part of the skull front behind the eye socket

The greater wing of the sphenoid bone, or alisphenoid, is a bony process of the sphenoid bone, positioned in the skull behind each eye. There is one on each side, extending from the side of the body of the sphenoid and curving upward, laterally, and backward.

<span class="mw-page-title-main">Squamous part of temporal bone</span> Front and upper part of the sides of the skull base

The squamous part of temporal bone, or temporal squama, forms the front and upper part of the temporal bone, and is scale-like, thin, and translucent.

<span class="mw-page-title-main">Infratemporal fossa</span> Cavity that is part of the skull

The infratemporal fossa is an irregularly shaped cavity that is a part of the skull. It is situated below and medial to the zygomatic arch. It is not fully enclosed by bone in all directions. It contains superficial muscles, including the lower part of the temporalis muscle, the lateral pterygoid muscle, and the medial pterygoid muscle. It also contains important blood vessels such as the middle meningeal artery, the pterygoid plexus, and the retromandibular vein, and nerves such as the mandibular nerve (CN V3) and its branches.

<span class="mw-page-title-main">Deep cervical fascia</span>

The deep cervical fascia lies under cover of the platysma, and invests the muscles of the neck; it also forms sheaths for the carotid vessels, and for the structures situated in front of the vertebral column. Its attachment to the hyoid bone prevents the formation of a dewlap.

<span class="mw-page-title-main">Coronoid process of the mandible</span>

In human anatomy, the mandible's coronoid process 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 continuous below with the anterior border of the ramus. Its posterior border is concave and forms the anterior boundary of the mandibular notch. The lateral surface is smooth, and affords insertion to the temporalis and masseter muscles. Its medial surface gives insertion to the temporalis, and presents a ridge which begins near the apex of the process and runs downward and forward to the inner side of the last molar tooth.

<span class="mw-page-title-main">Mandible</span> Lower jaw bone

In jawed vertebrates, the mandible, lower jaw, or jawbone is a bone that makes up the lower – and typically more mobile – component of the mouth.

Fascial spaces are potential spaces that exist between the fasciae and underlying organs and other tissues. In health, these spaces do not exist; they are only created by pathology, e.g. the spread of pus or cellulitis in an infection. The fascial spaces can also be opened during the dissection of a cadaver. The fascial spaces are different from the fasciae themselves, which are bands of connective tissue that surround structures, e.g. muscles. The opening of fascial spaces may be facilitated by pathogenic bacterial release of enzymes which cause tissue lysis. The spaces filled with loose areolar connective tissue may also be termed clefts. Other contents such as salivary glands, blood vessels, nerves and lymph nodes are dependent upon the location of the space. Those containing neurovascular tissue may also be termed compartments.

<span class="mw-page-title-main">Submasseteric space</span>

The submasseterric space is a fascial space of the head and neck. It is a potential space in the face over the angle of the jaw, and is paired on each side. It is located between the lateral aspect of the mandible and the medial aspect of the masseter muscle and its investing fascia. The term is derived from sub- meaning "under" in Latin and masseteric which refers to the masseter muscle. The submasseteric space is one of the four compartments of the masticator space. Sometimes the submasseteric space is described as a series of spaces, created because the masseter muscle has multiple insertions that cover most of the lateral surface of the ramus of the mandible.

<span class="mw-page-title-main">Infratemporal space</span>

The infratemporal space is a fascial space of the head and neck. It is a potential space in the side of the head, and is paired on either side. It is located posterior to the maxilla, between the lateral pterygoid plate of the sphenoid bone medially and by the base of skull superiorly. The term is derived from infra- meaning below and temporal which refers to the temporalis muscle.

References

  1. ↑ Elsevier, Dorland's Illustrated Medical Dictionary, Elsevier.
  2. ↑ Merriam-Webster, Merriam-Webster's Medical Dictionary, Merriam-Webster.
  3. ↑ Houghton Mifflin Harcourt, The American Heritage Dictionary of the English Language, Houghton Mifflin Harcourt, archived from the original on 2015-09-25, retrieved 2015-09-27.
  4. ↑ Wolters Kluwer, Stedman's Medical Dictionary, Wolters Kluwer.
  5. ↑ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. p. 283. ISBN   0-03-910284-X.
  6. ↑ Mezey, Szilvia E.; Müller-Gerbl, Magdalena; Toranelli, Mireille; Türp, Jens Christoph (2022-02-01). "The human masseter muscle revisited: First description of its coronoid part". Annals of Anatomy - Anatomischer Anzeiger. 240: 151879. doi: 10.1016/j.aanat.2021.151879 . ISSN   0940-9602. PMID   34863910. S2CID   244844284.
  7. ↑ Mudry, Albert; Jackler, Robert K. (2022-08-01). "The coronoid insertion of the human masseter muscle was well described in the 18th century". Annals of Anatomy - Anatomischer Anzeiger. 243: 151922. doi:10.1016/j.aanat.2022.151922. ISSN   0940-9602. PMID   35278659. S2CID   247374798.
  8. 1 2 Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, p. 97
  9. ↑ "Mix it up Monday: Releasing the masseter muscle". 14 December 2015.
  10. ↑ Kayes, Gillyane (2000). Singing and the Actor. ISBN   978-0878301980.
  11. ↑ Takeuchi, Hayate; Matsuishi, Takashi Fritz; Hayakawa, Takashi (2024). "A tradeoff evolution between acoustic fat bodies and skull muscles in toothed whales". Gene. 901: 148167. doi:10.1016/j.gene.2024.148167.
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