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 i ...

, 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 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 animals ...

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

. 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 in development.

Variation

The temporalis muscle has a complex structure. Sarcomeres are a consistent length, but larger

muscle fibres A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a musc ...

vary in length in the muscle and between people.

Function

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

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...

. During pterional craniotomy, 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