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The mandible, or jaw bone, is the only bone in the human body that moves while eating, talking, and performing other activities. The muscles of mastication are a group of muscles that enable the mandible's movements at the temporomandibular joint (TMJ). These include elevation, depression, protrusion, retraction, and side-to-side movement. The muscles responsible for elevating the mandible include the masseter, temporalis, and medial pterygoid.
| Characteristics | Values |
|---|---|
| Number of muscles that elevate the mandible | 4 |
| Names of muscles | Masseter, Temporalis, Medial Pterygoid, Lateral Pterygoid |
| Muscle fibre orientation | Vertical, oblique, horizontal |
| Function | Elevation, depression, protrusion, retraction, side-to-side movement |
| Innervation | Mandibular nerve (V3) |
| Blood supply | Maxillary artery |
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What You'll Learn
The masseter muscle
The fibres of the superficial portion pass inferior-posteriorly over the deep portion and insert onto the angle of the mandible (masseteric tubercle) and the inferior portion of the lateral surface of the mandibular ramus. The deep portion of the masseter muscle originates from the entire surface of the zygomatic arch, with the fibres running inferiorly and inserting along the mandibular ramus superior to the masseter muscle's superior portion. The entire superficial (lateral) aspect of the muscle is covered with thin but very strong masseteric fascia. The masseter muscle can become enlarged in patients who habitually clench or grind their teeth, even in those who constantly chew gum.
The masseter parallels the medial pterygoid muscle, but it is stronger and has superficial fibres that can cause protrusion. The medial aspect of the masseter muscle forms the lateral wall of the facial space, called the submasseteric space. It is a paired potential space between the lateral aspect of the mandible and the medial aspect of the masseter muscle.
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The temporalis muscle
The anterior and mid fibres of the temporalis muscle are responsible for elevating the mandible. The contraction of the anterior fibres moves the mandible dorsocranially, resulting in the elevation of the mandible and the closing of the mouth. The posterior fibres of the temporalis muscle function to retract the mandible, pulling it backward. The unilateral contraction of the temporalis muscle also contributes to the side-to-side grinding movement of the jaw.
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The medial pterygoid muscle
The superficial head of the medial pterygoid muscle originates from the maxillary tuberosity and the pyramidal process of the palatine bone. The deep head, which forms the bulk of the muscle, arises from the medial aspect of the lateral pterygoid plate of the sphenoid bone and from the pyramidal process of the palatine bone. Both heads attach to the ramus of the mandible near the angle of the mandible. The outer surface of the muscle lies against the inner surface of the mandible, from which it is separated by the lateral pterygoid muscle, sphenomandibular ligament, maxillary artery, mandibular nerve, and its lingual and inferior alveolar branches.
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The lateral pterygoid muscle
The lateral pterygoid is a two-headed, fan-shaped muscle located laterally in the infratemporal fossa of the skull. It comprises the medial wall of the infratemporal fossa and is contained within the masticator space. The muscle is supplied by the lateral pterygoid nerve, a branch of the mandibular nerve (CN V3), itself a branch of the trigeminal nerve (CN V). Its blood supply is derived from the pterygoid branches of the maxillary artery.
The two heads of the lateral pterygoid muscle are the superior (upper) and inferior (lower) heads. The superior head is formed by the most superomedial fibres of the muscle, while the inferior head is much wider and originates from the lateral surface of the lateral pterygoid plate of the sphenoid bone. 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 temporomandibular joint (TMJ), while the inferior fibres insert into the pterygoid fovea on the neck of the condyloid process of the mandible.
The primary function of the lateral pterygoid muscle is to control the function of the jaw and temporomandibular joint. It is the major protractor of the mandible and the only muscle of mastication that participates in depressing the mandible. The unilateral contraction of the lateral pterygoid muscle with the ipsilateral medial pterygoid muscle results in lateral mandibular movement to the contralateral side. When both bellies of the muscle contract bilaterally, the mandible travels anteriorly (protrusion). The lateral pterygoid muscle is also involved in the generation of horizontal forces required during mastication and parafunctional activities.
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The muscles of mastication
The masseter muscle is a strong, quadrangular muscle that covers the lateral aspect of the ramus of the mandible. It is composed of two layers that differ in their attachments. The larger, superficial layer arises from the maxillary process of the zygomatic bone and the anterior two-thirds of the zygomatic arch. The deep layer arises from the medial surface and inferior margin of the zygomatic arch. The masseter's major function is to elevate the mandible, with a minor contribution to protrusion. It is innervated by the masseteric nerve, a branch of the mandibular nerve.
The temporalis muscle is a large, flat, fan-shaped muscle that lies within the temporal fossa of the skull. Its fibres converge anteriorly to form a tendon that inserts on the apex and medial surface of the coronoid process and the anterior border of the ramus of the mandible. The function of the anterior and mid fibres of the temporalis muscle is to elevate the mandible, while the posterior fibres function to retract the mandible. It is innervated by the deep temporal branches of the mandibular nerve.
The medial pterygoid muscle is a quadrangular muscle situated in the infratemporal fossa. It has two heads: a larger deep head and a smaller superficial head. Both heads attach to the ramus of the mandible near the angle of the mandible. The medial pterygoid functions to assist with elevation and protrusion of the mandible, as well as side-to-side mandibular motion for grinding food. It is innervated by the medial pterygoid nerve, a division of the mandibular nerve.
The lateral pterygoid muscle is the sole muscle of mastication that causes depression of the mandible. It also assists with protrusion and side-to-side movement. It has two heads: superior and inferior. The superior head originates from the greater wing of the sphenoid, while the inferior head originates from the lateral pterygoid plate of the sphenoid. The two heads converge into a tendon that attaches to the neck of the mandible.
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Frequently asked questions
The muscles that elevate the mandible are the masseter, temporalis, medial pterygoid, and lateral pterygoid.
The masseter muscle's main function is to elevate the mandible and approximate the teeth.
The temporalis muscle fibres converge to form a tendon that exits the temporal fossa and inserts on the coronoid process of the mandible. Its main function is to elevate the mandible.
