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The muscles responsible for chewing are known as the muscles of mastication. These consist of the temporalis, masseter, medial pterygoid, and lateral pterygoid muscles. They are innervated by the mandibular branch of the trigeminal nerve, which is both sensory and motor. The muscles of mastication develop from the first pharyngeal arch and attach to the mandible, producing movements of the lower jaw at the temporomandibular joint (TMJ).
| Characteristics | Values |
|---|---|
| Primary muscles | Temporalis, medial pterygoid, lateral pterygoid, masseter |
| Accessory muscles | Buccinator, suprahyoid, infrahyoid |
| Origin of muscles | Skull |
| Functions | Elevation, depression, protrusion, retraction, side-to-side movement, grinding, closing the mouth |
| Innervation | Mandibular nerve (V3), a branch of the trigeminal nerve (CN V) |
| Blood supply | Maxillary artery, a branch of the external carotid artery |
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What You'll Learn
The temporalis muscle
The unilateral contraction of the temporalis muscle is important for side-to-side movements of the jaw, which assists in the grinding of food during the process of eating. The temporalis muscle is innervated by the mandibular nerve (V3), which is the third division of the trigeminal nerve. It receives its blood supply from the deep temporal branches of the maxillary artery and the middle temporal branches of the superficial temporal artery.
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The masseter muscle
The word "masseter" comes from the Greek "masasthai," meaning "to chew." The masseter muscle is one of the muscles of mastication, which develop from the first pharyngeal arch. These muscles are innervated by the mandibular nerve (V3), which is the third division of the trigeminal nerve. The mandibular nerve carries both sensory and motor fibres and innervates all four main muscles of mastication: the masseter, temporalis, medial pterygoid, and lateral pterygoid.
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The medial pterygoid muscle
The origin and insertion of the medial pterygoid muscle vary depending on the head. The superficial head originates from the maxillary tuberosity and the pyramidal process of the palatine bone. The deep head originates from the medial surface of the lateral pterygoid plate of the sphenoid bone and the pyramidal process of the palatine bone. From their origin, the muscle fibres run posteroinferiorly and laterally, surrounding the lower fibres of the lateral pterygoid muscle.
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The lateral pterygoid muscle
The fibres from both heads converge to course posterolaterally in a predominantly horizontal plane. The superior fibres insert into the anteromedial part of the articular capsule and articular disc of the TMJ. The inferior fibres insert into the pterygoid fovea on the neck of the condyloid process of the mandible. The superior attachment onto the TMJ enables the muscle head to act on the superior compartment of the joint, facilitating gliding motions of the disc and mandibular condyle. On the other hand, the inferior head acts on the inferior compartment of the TMJ, facilitating a hinge-like rotation between the mandibular condyle and the inferior surface of the articular disc.
The primary function of the lateral pterygoid muscle is to control the function of the jaw and TMJ. It is the only muscle among the four muscles of mastication that participates in depressing the mandible. It does so by protruding and depressing the mandible when contracting bilaterally and by rotating the mandible when contracting unilaterally. The unilateral contraction of the lateral pterygoid muscle with the ipsilateral medial pterygoid muscle results in lateral mandibular movement to the contralateral side. This movement is observable during chewing, masticating, and clenching.
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The accessory muscles
The temporalis muscle is fan-shaped and originates from the temporal fossa of the skull, passing underneath the zygomatic arch to insert on the coronoid process of the mandible. Its functions include elevating the mandible (closing the mouth) and retracting the mandible (moving the jaw backward). The medial pterygoid muscle is thick and rectangular, with a superficial head and a deep head. It assists with elevating and protruding the mandible, as well as side-to-side mandibular motion for grinding food.
The lateral pterygoid muscle is triangular with two heads: the superior and inferior. It is responsible for depressing the mandible (opening the mouth), as well as assisting with protrusion and side-to-side movement of the mandible. The masseter muscle is quadrangular and has two parts: deep and superficial. It is the most powerful muscle of mastication, responsible for elevating the mandible and approximating the teeth.
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Frequently asked questions
The muscles that aid in chewing are the temporalis, masseter, medial pterygoid, and lateral pterygoid muscles.
The temporalis muscle is a fan-shaped muscle that aids in the elevation of the mandible (closing the mouth) and retraction of the mandible (moving the jaw backward).
The masseter muscle is the most powerful muscle of mastication. It functions to elevate the mandible, approximate the teeth, and retract the mandible.
The medial pterygoid muscle functions to assist with the elevation and protrusion of the mandible, as well as side-to-side movement of the jaw during grinding and chewing.
The function of the lateral pterygoid muscle depends on the degree of its contraction. Bilateral contraction of this muscle depresses and protrudes the mandible, while unilateral contraction moves the mandible to the opposite side, allowing for side-to-side movement during chewing.
