anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...

, 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 The temporal fossa is a fossa (shallow depression) on the side of the skull bounded by the temporal lines and terminating below the level of the zygomatic arch. Boundaries * Medial: frontal bone, parietal bone, temporal bone, and sphenoid bon ...

, superior to the

zygomatic arch In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal process of the zygo ...

so it covers much of 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. ...

.Illustrated Anatomy of the Head and Neck, Fehrenbach and Herring, Elsevier, 2012, page 98''Temporal'' refers to the head's

temples A temple (from the Latin ) is a building reserved for spiritual rituals and activities such as prayer and sacrifice. Religions which erect temples include Christianity (whose temples are typically called churches), Hinduism (whose temples ...

Structure

In humans, the temporalis muscle arises from the

and the deep part of

temporal fascia The temporal fascia covers the temporalis muscle. It is a strong, fibrous investment, covered, laterally, by the auricularis anterior and superior, by the galea aponeurotica, and by part of the orbicularis oculi. The superficial temporal vesse ...

. This is a very broad area of attachment. It passes medial to the

. It forms a tendon which inserts onto 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 ...

, with its insertion extending into the retromolar fossa posterior to the most distal mandibular molar.Human Anatomy, Jacobs, Elsevier, 2008, page 194 In other mammals, the muscle usually spans the dorsal part of the skull all the way up to the medial line. There, it may be attached to a sagittal crest, as can be seen in early hominins such as ''

Paranthropus aethiopicus ''Paranthropus aethiopicus'' is an extinct species of robust australopithecine from the Late Pliocene to Early Pleistocene of East Africa about 2.7–2.3 million years ago. However, it is much debated whether or not ''Paranthropus'' is an invali ...

''. The temporalis muscle is covered by the

, also known as the temporal aponeurosis. This fascia is commonly used in

tympanoplasty Tympanoplasty is the surgical operation performed to reconstruct hearing mechanism of middle ear Classification Tympanoplasty is classified into five different types, originally described by Horst Ludwig Wullstein (1906–1987) in 1956. # Type ...

, or surgical reconstruction of the eardrum. The temporalis muscle is accessible on the

, and can be seen and felt contracting while the jaw is clenching and unclenching.

Blood supply

The muscle receives its blood supply from the

deep temporal arteries The deep temporal arteries are two arteries of the head. They ascend between the temporalis muscle and the pericranium. They anastomose with the middle temporal artery, among other vessels. They supply the temporalis muscle. Structure The deep ...

which anastomose with the

middle temporal artery In anatomy, the middle temporal artery is a major artery which arises immediately above the zygomatic arch, and, perforating the temporal fascia, gives branches to the temporalis, anastomosing with the deep temporal branches of the internal max ...

Nerve supply

As with the other muscles of mastication, control of the temporal muscle comes from the third (mandibular) branch of 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 chew ...

. Specifically, the muscle is supplied by the

deep temporal nerves The deep temporal nerves are two branches of the anterior division of the mandibular nerve that innervate the temporalis. Structure The deep temporal nerves are usually two in number and termed the anterior deep temporal nerve and posterior deep ...

. At least 6 smaller branches recruit muscle fibres the most when each has the maximal leverage.

Development

The temporalis muscle is derived 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 arche ...

in development.

Variation

The temporalis muscle has a complex structure.

Sarcomeres A sarcomere (Greek σάρξ ''sarx'' "flesh", μέρος ''meros'' "part") is the smallest functional unit of striated muscle tissue. It is the repeating unit between two Z-lines. Skeletal muscles are composed of tubular muscle cells (called musc ...

are a consistent length, but larger muscle fibres vary in length in the muscle and between people.

Function

The temporalis muscle is the most powerful muscle of 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 ...

. The temporalis muscle can be divided into two functional parts; anterior and posterior. The anterior portion runs vertically and its contraction results in elevation of the mandible (closing the mouth). The posterior portion has fibers which run horizontally and contraction of this portion results in retrusion of the mandible. The middle portion which fibers run in an oblique direction towards inferior and anterior are used for both elevation and retraction of the mandible and in a unilateral contraction provoke lateral movement of the mandible. Motor units are recruited the most when they have the maximal leverage, maximising contractile strength. When lower dentures are fitted, they should not extend into the retromolar fossa to prevent trauma of the mucosa due to the contraction of the temporalis muscle.

Clinical significance

Face of man with hypertrophy of the temporal muscles Wellcome L0062508

The temporalis muscle is likely to be involved in jaw pain and headaches. Bruxism, the habitual grinding of teeth typically while sleeping, and clenching of the jaw while stressed can lead to overwork of the temporalis muscle and results in pain.

Seizure

A myotendinous rupture of the temporalis muscle can occur during a seizure due to extreme clenching of the jaw. During a seizure, the contralateral temporalis muscle can enter spastic paralysis, this clenching in extreme cases can lead to a rupture specifically on the myotendinous insertion at the coronoid process of the mandible.

Surgery

The temporalis muscle may be used in

reconstructive surgery Reconstructive surgery is surgery performed to restore normal appearance and function to body parts malformed by a disease or medical condition. Description Reconstructive surgery is a term with training, clinical, and reimbursement implicat ...

of the mouth. During pterional

craniotomy A craniotomy is a surgical operation in which a bone flap is temporarily removed from the skull to access the brain. Craniotomies are often critical operations, performed on patients who are suffering from brain lesions, such as tumors, blood clot ...

, incisions are often chosen based on the ease of reattaching the temporalis muscle after the bone fragment is replaced.

Additional images

File:Temporal muscle animation small.gif, Temporal muscle (red). File:Illu head neck muscle.jpg, Muscles of head and neck File:Slide8por.JPG, Temporal muscle.Deep dissection.Mummification process.

References

External links

* - "Infratemporal Fossa: The Temporalis Muscle" * * Temporalis Muscle Transfer, The Methodist Hospital System, Houston, TX, at http://www.methodistfacialparalysis.com/temporalis/ {{Authority control Muscles of the head and neck