Victor Forge
The muscles of mastication are a group of muscles that enable chewing, grinding food, and talking. They are the primary movers of the mandible, which is the only bone that moves during mastication. The four main muscles of mastication are the masseter, temporalis, medial pterygoid, and lateral pterygoid. These muscles are responsible for opening and closing the mouth by influencing motion on the mandible. The masseter, for example, originates from the zygomatic arch and inserts along the angle and lateral surface of the mandible, providing powerful elevation and protrusion of the mandible. Other muscles, such as those of the tongue, cheeks, and neck, also play a role in mastication and help with the process of opening the mouth.
| Characteristics | Values |
|---|---|
| Muscles of mastication | Masseter, Temporalis, Medial Pterygoid, Lateral Pterygoid |
| Function | Open and close the mouth by moving the mandible |
| Origin | Surface of the skull |
| Attachment | Rami of the mandible at the temporomandibular joint (TMJ) |
| Movements | Elevation, Depression, Protrusion, Retraction, Side to Side |
| Innervation | Trigeminal nerve (CN V3) |
| Arterial Supply | Maxillary artery |
| Accessory Muscles | Buccinator, Suprahyoid, Infrahyoid |
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What You'll Learn
The masseter muscle
The masseter is one of the four primary muscles of mastication (the chewing movement of the mandible at the temporomandibular joint). The other three muscles of mastication are the temporalis, medial pterygoid, and lateral pterygoid. The masseter muscle is a powerful, thick, and rectangular muscle that originates from the zygomatic arch and inserts along the angle and lateral surface of the mandibular ramus. It consists of two parts: a superficial portion and a deep portion. The superficial portion of the masseter muscle originates from the temporal process of the zygomatic bone and the anterior two-thirds of the inferior border of the zygomatic arch. The deep portion of the masseter muscle originates from the entire surface of the zygomatic arch.
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The temporalis muscle
The auriculotemporal, facial and zygomaticotemporal nerves run across the superficial aspect of the temporalis muscle. The temporalis muscle receives its innervation from the anterior, middle and posterior deep temporal branches of the anterior trunk of the mandibular nerve (V3). The temporalis muscle is likely to be involved in jaw pain and headaches. Bruxism, the habitual grinding of teeth, and clenching of the jaw while stressed can lead to overwork of the temporalis muscle and result in pain.
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The medial pterygoid muscle
The unilateral contraction of the medial pterygoid muscle causes a slight medial rotation of the mandible. When this occurs simultaneously with the contraction of the ipsilateral lateral pterygoid, it results in a noticeable movement where the same-sided part of the mandible swings anteriorly and medially. On the other hand, bilateral contraction of the medial pterygoid muscle elevates and protrudes the mandible, facilitating the act of chewing and closing the mouth.
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The lateral pterygoid muscle
Fibers from both heads converge to course posterolaterally in a predominantly horizontal plane. The superior fibers insert into the anteromedial part of the articular capsule and articular disc of the temporomandibular joint. The inferior fibers, on the other hand, insert into the pterygoid fovea on the neck of the condyloid process of the mandible. The superior attachment onto the temporomandibular joint allows the muscle head to act on the superior compartment of the joint, facilitating the gliding motions of the disc and mandibular condyle. The inferior head, in contrast, acts on the inferior compartment of the TMJ, enabling 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 temporomandibular joint. It is the only muscle among the four muscles of mastication that participates in depressing the mandible (opening the jaw). 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 functional and parafunctional lateral excursive movements, such as chewing, masticating, and clenching. When both bellies of the lateral pterygoid muscle contract bilaterally, the mandible moves forward (protrusion). The lateral pterygoid muscle is supplied by the lateral pterygoid nerve, a branch of the mandibular nerve (CN V3), which is itself a branch of the trigeminal nerve (CN V).
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The buccinator, a facial expression muscle
The human face has about 20 main facial muscles that are essential for chewing and making facial expressions. The buccinator muscle is one of these muscles and is the main component of the cheek. It is a thin, quadrilateral facial muscle that belongs to the buccolabial group of facial muscles. The buccinator has several origin points, which is the basis for subdividing the muscle fibres into superior, inferior, and posterior parts.
The superior part of the buccinator muscle arises from the outer surface of the alveolar process of the maxilla, opposite to the three maxillary molar teeth. The inferior part arises from the alveolar part of the mandible, opposite to the three mandibular molar teeth. The posterior part originates from the anterior margin of the pterygomandibular raphe, a tendinous band behind the third molar, spanning from the pterygoid hamulus to the posterior end of the mylohyoid line. Some of the posterior fibres attach to the buccinator crest, a small ridge on the retromolar triangle. Additionally, some fibres of the buccinator arise from the pterygomaxillary raphe, a fibrous band that extends from the pterygoid hamulus to the maxillary tuberosity.
The buccinator muscle is located between the mandible and maxilla, deep to the other muscles of the face. The fibres run in an inferomedial direction, blending with the orbicularis oris muscle and the skin of the lips. The buccinator pulls the cheek inwards against the teeth, preventing the accumulation of food in that area. It compresses the cheek against the molar teeth, which is important for keeping food centralised in the oral cavity and preventing the cheeks from being bitten during mastication.
The buccinator muscle is innervated by the buccal branches of the facial nerve and receives its blood supply from the buccal artery, a branch of the maxillary artery. The buccal nerve and artery, as well as the facial artery and vein, cross the surface of the muscle. The duct of the parotid gland also courses over this surface and pierces the buccinator at the level of the third upper molar tooth. The deep surface of the buccinator is related to the structures of the oral cavity, including the buccal glands and mucous membrane of the mouth.
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Frequently asked questions
The muscles that open the mouth are the masseter, temporalis, medial pterygoid, and lateral pterygoid.
The masseter muscle provides powerful elevation and protrusion of the mandible. It originates from the zygomatic arch and inserts along the angle and lateral surface of the mandible.
The accessory muscles of mastication are the buccinator, suprahyoid, digastric, mylohyoid, geniohyoid, sternohyoid, sternothyroid, thyrohyoid, and omohyoid muscles.
