Victor Forge
The mandible is the only bone that moves during mastication (chewing) and other activities such as talking. The muscles of mastication are a group of muscles responsible for the chewing movement of the mandible at the temporomandibular (TMJ) joint. They enhance the process of eating, assist in grinding food, and function to approximate the teeth. The primary muscles of mastication are the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles. The lateral pterygoid muscle is responsible for opening the jaw, while the other three muscles are responsible for closing the mandible.
| Characteristics | Values |
|---|---|
| Primary muscles of mastication | Temporalis, medial pterygoid, lateral pterygoid, and masseter muscles |
| Function of the temporalis muscle | Elevate the mandible |
| Function of the lateral pterygoid muscle | Open the mandible |
| Function of the masseter muscle | Elevate the mandible |
| Function of the medial pterygoid muscle | Elevate the mandible |
| Accessory muscles of mastication | Digastric, geniohyoid, mylohyoid, omohyoid, sternohyoid, sternothyroid, stylohyoid, and thyrohyoid muscles |
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What You'll Learn
The temporalis muscle
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. The contraction of the anterior fibres moves the mandible dorsocranially (elevation), while the contraction of the posterior fibres pulls the mandible posteriorly (retrusion). The unilateral contraction of the temporalis muscle is involved in the side-to-side movement of the jaw.
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The medial pterygoid muscle
The superficial head of the medial pterygoid originates from the maxillary tuberosity of the inferior maxilla 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. The fibres from both heads converge inferiorly, forming a tendon that inserts onto the triangular impression located on the medial surface of the mandible.
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The lateral pterygoid muscle
The fibres from both heads converge and insert into different parts of the temporomandibular joint (TMJ). The superior fibres attach to the anteromedial part of the articular capsule and articular disc of the TMJ, while the inferior fibres attach to the pterygoid fovea on the neck of the condyloid process of the mandible. This attachment enables the muscle to act on both the superior and inferior compartments of the TMJ, facilitating gliding motions and hinge-like rotations between the mandibular condyle and the articular disc.
The primary function of the lateral pterygoid muscle is to control the function of the jaw and TMJ, generating horizontal forces during mastication and parafunctional activities. It is involved in protrusion (forward movement of the mandible), abduction (depression of the mandible), and mediotrusion (movement of the mandibular condyle towards the midline). The muscle is active during speaking, singing, and clenching, and it is the major protractor of the mandible. When contracting unilaterally, the lateral pterygoid muscle causes contralateral excursion, a form of mastication, and can move the mandible side to side. When contracting bilaterally, the muscle protrudes the mandible.
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The masseter muscle
The word "masseter" originates from the Greek word "masasthai," which means "to chew," reflecting its crucial role in the chewing or mastication process.
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Accessory muscles
The muscles of mastication are a group of muscles responsible for the chewing movement of the mandible at the temporomandibular joint (TMJ). The four main muscles of mastication are the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles. These muscles attach to the rami of the mandible and function to move the jaw.
The temporalis muscle is a fan-shaped muscle with anterior, mid, and posterior fibres. The origin of the temporalis muscle spans from the temporal fossa to the inferior temporal line of the lateral skull. 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. The temporalis muscle also contributes to side-to-side grinding movements.
The medial pterygoid muscle is a thick rectangular muscle with a superficial head and a deep head. The superficial head originates from the maxillary tuberosity of the inferior maxilla, while the deep head originates from the medial surface of the lateral pterygoid plate of the sphenoid bone. The medial pterygoid muscle functions to assist with elevation and protrusion of the mandible, as well as side-to-side mandibular motion to help with grinding food.
The lateral pterygoid muscle has two parts: an upper head and a lower head. The upper head originates from the inferior temporal surface of the greater wing of the sphenoid bone, while the lower head originates from the lateral aspect of the lateral pterygoid plate of the sphenoid bone. The lateral pterygoid muscle functions as the sole muscle of mastication that causes depression of the mandible, as well as assisting with protrusion and side-to-side movement.
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: a larger, superficial layer that arises from the maxillary process of the zygomatic bone and the anterior two-thirds of the zygomatic arch, and a deep layer that arises from the medial surface and inferior margin of the zygomatic arch. The major function of the masseter muscle is to elevate the mandible and approximate the teeth, while the intermediate and deep muscle fibres function to retract the mandible and the superficial fibres function to protrude the mandible.
In addition to these four main muscles of mastication, there are also accessory muscles that assist in the movement of the mandible. These include the platysma muscle, a superficial muscle of the neck that assists with depression of the mandible against resistance, and the buccinator, a facial expression muscle that helps in mastication by keeping food pushed back within the oral cavity.
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Frequently asked questions
The primary muscles of mastication (chewing food) are the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles.
The functions of the temporalis muscle are to elevate the mandible and retract it, pulling the jaw backward.
The major function of the masseter muscle is to elevate the mandible, with a minor contribution to protrusion.
The medial pterygoid muscle functions to assist with elevation and protrusion of the mandible. It also assists the lateral pterygoid muscle with side-to-side mandibular motion to help with the grinding of food.
The accessory muscles that help open the mandible include the digastric, geniohyoid, mylohyoid, omohyoid, sternohyoid, sternothyroid, stylohyoid, and thyrohyoid muscles.
