anatomy Anatomy () is the branch of morphology concerned with the study of the internal 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 scien ...

, the temporalis muscle, also known as the temporal muscle, is one of the

muscles of mastication The four classical muscles of mastication elevate the mandible (closing the jaw) and move it forward/backward and laterally, facilitating biting and chewing. Other muscles are responsible for opening the jaw, namely the geniohyoid, mylohyoid, an ...

(chewing). It is a broad, fan-shaped convergent

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

on each side of the

head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple ani ...

that fills the temporal fossa, superior to the zygomatic arch so it covers much of the

temporal bone The temporal bone is a paired bone situated at the sides and base of the skull, lateral to the temporal lobe of the cerebral cortex. The temporal bones are overlaid by the sides of the head known as the temples where four of the cranial bone ...

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

Structure

In humans, the temporalis muscle arises from the temporal fossa and the deep part of temporal fascia. This is a very broad area of attachment. It passes medial to the zygomatic arch. It forms a tendon which inserts onto the coronoid process of the mandible, 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 A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are excepti ...

, as can be seen in early hominins such as '' Paranthropus aethiopicus''. The temporalis muscle is covered by the temporal fascia, also known as the temporal aponeurosis. This fascia is commonly used in tympanoplasty, or surgical reconstruction of the eardrum. The temporalis muscle is accessible on the temples, and can be seen and felt

contracting A contract is an agreement that specifies certain legally enforceable rights and obligations pertaining to two or more parties. A contract typically involves consent to transfer of goods, services, money, or promise to transfer any of those a ...

while the jaw is clenching and unclenching.

Blood supply

The muscle receives its blood supply from the deep temporal arteries which anastomose with the middle temporal artery.

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 (literal translation, lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for Sense, sensation in the face and motor functions ...

. Specifically, the muscle is supplied by the deep temporal nerves. 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 transient structures seen in the embryonic development of humans and other vertebrates, that are recognisable precursors for many structures. In fish, the arches support the gills a ...

in development.

Variation

The temporalis muscle has a complex structure. Sarcomeres are a consistent length, but larger muscle fibres vary in length in the muscle and between people.

Function

The temporalis muscle is a 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 joint, synovial articulation between the temporal bone of the skull above and the condylar process of mandible be ...

. 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 Bruxism is excessive teeth grinding or jaw clenching. It is an oral Parafunctional habit, parafunctional activity; i.e., it is unrelated to normal function such as eating or talking. Bruxism is a common behavior; the global prevalence of brux ...

, 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 A mouth also referred to as the oral is the body orifice through which many animals ingest food and animal communication#Auditory, vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also t ...

. During pterional

craniotomy A craniotomy is a surgery, surgical operation in which a bone flap is temporarily removed from the Human skull, skull to access the Human brain, brain. Craniotomies are often critical operations, performed on patients who are suffering from brain ...

, 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