Table of Contents
- Temporalis Muscle
- Temporalis Origin and Insertion
- Temporalis Function
- Temporalis Muscle Innervation
- Temporalis Muscle Blood Supply
- Lesson Summary
The temporalis muscle is a thin, but broad muscle. The shape of the temporalis muscle is like that of a fan. This muscle is sometimes referred to as the temporal muscle. The anterior portion of the temporalis muscle is made up of vertically oriented fibers; while the middle portion consists of obliquely oriented fibers. The posterior portion has fibers with a horizontal orientation.
Along with the masseter, lateral pterygoid, and medial pterygoid muscles, the temporalis muscle belongs to the masticatory muscle group. This muscle plays a very important role in mastication, as it works to allow the movements of the mandible— or lower jaw—at the temporomandibular joint. These movements help in biting and mastication—or mechanical breakdown—of the food, with the help of teeth in the mouth. The anterior fibers of the muscle help the lower jaw move dorsocranially; however, its posterior portion is helpful in pulling the lower jaw posteriorly. Due to this supportive influence of temporalis muscle fibers, the mandible can elevate and retract to facilitate the act of mastication.
The temporalis muscle is located within the temporal fossa. The temporal fossa is a depression, or indented area, within the temporal bone of the skull. This muscle generally fills most of the fossa present on both sides of the skull.
The point of origin of the temporalis muscle bridges the whole surface of the temporal fossa that is usually located below the temporal line. However, some of its fibers also arise from the temporal fascia, which lies under the skin and covers the temporal bone.
The vertically-directed anterior fibers and horizontally-directed posterior fibers of the temporalis muscle converge together onto a tendon that extends downward to the zygomatic arch. This narrow tendon further attaches onto the apex, medial surface, and anterior portion of the coronoid process of the mandible. The tendon also attaches on the anterior border of the ascending part of the ramus of the mandible in such a way that this tendon appears nearly as far forward as an individual's last molar tooth.
The temporalis muscle is considered the strongest muscle associated with the temporomandibular joint. It is also the primary muscle that serves to retract the mandible. The main function of the temporalis muscle is chewing, which is facilitated by the contractions of its fibers. This muscle is also helpful in the biting process. When the anterior fibers of the temporalis muscle contract, it facilitates elevation—or dorsocranial movements—of the mandible. However, the contraction of its posterior fibers causes the mandible to move backward in retraction. Along with the closing of the mouth, these actions also help in the approximation of teeth. In addition to elevation and retraction, the side-to-side movements of the mandible are facilitated when the temporalis muscle contracts unilaterally.
The process in which the brain sends the electrical impulses to the temporalis muscle through a network of nerves is known as innervation. The cranial nerve V is mainly responsible for carrying the electrical impulses from the brain to the temporalis muscle, and thus, controls the functioning of the temporal muscle. The trigeminal nerve is another name for the cranial nerve V. It is the largest and most complex nerve of the 12 cranial nerves of humans.
The trigeminal nerve further divides into three large branches, which include the mandibular, the maxillary, and the ophthalmic branch. Each branch of the nerve carries the sensory signals, respectively, from the lower, middle, and upper portions of the face to the brain. The mandibular division of the trigeminal nerve carries the sensory signals from the mucous membrane of the cheek and mouth, side of the head and scalp, two-thirds of the tongue's anterior portion, the skin of the mandible, lower teeth, meninges of the anterior, and the middle cranial fossae. Thus, the temporalis muscle is more specifically innervated by the mandibular branch of cranial nerve V. The maxillary division innervates the skin of the lower eyelid, the alar part of the nose, the prominence of the cheek, the upper lip, the maxilla (upper jaw), and a part of the temple. The ophthalmic division of the trigeminal nerve is responsible for innervating various eye structures, including the cornea, conjunctiva, lacrimal gland, and ciliary body. In addition, the part of the mucous membrane of the nasal cavity and the skin of eyebrows, eyelids, nose, and forehead are also supplied through the ophthalmic branch of the trigeminal nerve.
In humans, the external carotid artery found in the head region divides into two terminal branches, which include the internal maxillary artery and the superficial temporal artery. The larger branch of the external carotid artery is referred to as the internal maxillary artery, which is commonly divided into three parts: mandibular, pterygoid, and pterygopalatine. The mandibular and pterygoid parts have five branches each, while the pterygopalatine part has six branches, including the terminal branch. The temporalis muscle receives the blood supply from anterior and posterior deep temporal arterial branches of the muscular pterygoid part of the internal maxillary artery. Along with these two arteries, a branch of the superficial temporal artery called the middle temporal artery also has its contributions in supplying blood to the temporalis muscle.
In humans, a fan-shaped temporalis muscle (also known as the temporal muscle) is found within a depressed or indented area of the temporal bone of the skull. The fibers of this masticatory muscle collectively arise from the temporal fossa and temporal fascia. Once originated, these muscle fibers converge into a narrow tendon that inserts to the coronoid process and ramus of the mandible. The temporalis muscle is primarily responsible for facilitating the elevation, retraction, and side-to-side movements of the mandible or lower jaw at the temporomandibular joint. These movements are helpful in biting and chewing or mastication of food in the mouth. Cranial nerve V also called the trigeminal nerve, carries the information from the brain to the temporalis muscle. The blood supply to the temporalis muscle is made possible through anterior and posterior deep temporal arterial branches of along with the medial temporal artery. The anterior and posterior temporal arterial branches arise from the internal maxillary artery that descends from the external carotid artery. However, another branch of this carotid artery is superficial temporal artery gives rise to the medial temporal artery.
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The temporalis muscle is primarily responsible for facilitating the act of mastication. This muscle, inserted into the coronoid process and ramus of the mandible, helps the lower jaw to move up, backward, and side-to-side at the temporomandibular joint. These movements collectively help in biting and chewing food in the mouth.
The temporalis muscle causes elevation, retraction, and side-to-side movements of the mandible. Anterior fibers of this muscle contract, facilitating dorsocranial movements of the mandible; while the contraction of posterior fibers causes retraction, or backward movement, of the mandible. Unilateral contraction of the temporalis muscle produces side-to-side movements of the lower jaw.
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