Dominic Stone
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 four main muscles of mastication are the masseter, temporalis, medial pterygoid, and lateral pterygoid. This paragraph will focus on the muscle that protracts the mandible.
| Characteristics | Values |
|---|---|
| Number of muscles of mastication | 4 |
| Muscle names | Masseter, temporalis, medial pterygoid, lateral pterygoid |
| Muscle functions | Elevation, depression, protrusion, retraction, side-to-side movement |
| Muscle origins | Skull bones |
| Muscle insertions | Various features of the mandible |
| Innervation | Motor branches of the mandibular division of the trigeminal nerve (CNV3) |
| Arterial supply | Branches of the maxillary artery |
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What You'll Learn
The masseter muscle
The primary function of the masseter muscle is the elevation of the mandible, which causes the mouth to close. In addition, the masseter also plays a role in the protrusion of the mandible. The contraction of the superior part of the masseter muscle moves the mandible forward, resulting in protrusion. The deep fibres of the masseter muscle contribute to the retraction of the mandible, while the superficial fibres are responsible for its protrusion. The masseter muscle also provides support to the articular capsule of the temporomandibular joint, helping to stabilise tension in this area.
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The temporalis muscle
The anterior fibres of the temporalis muscle have a vertical orientation, while the mid fibres have an oblique orientation and the posterior fibres have a horizontal orientation. The contraction of the anterior fibres moves the mandible dorsocranially (elevation), facilitating the closing of the mouth. On the other hand, the contraction of the posterior fibres pulls the mandible backward (retrusion). The unilateral contraction of the temporalis muscle is also important for the side-to-side movement of the jaw.
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The medial pterygoid muscle
The function of the medial pterygoid muscle includes elevating and protruding the mandible, as well as assisting with mastication. The unilateral contraction of the medial pterygoid causes a slight medial rotation of the mandible, and when this occurs simultaneously with the contraction of the ipsilateral lateral pterygoid, it results in a noticeable movement of the mandible swinging anteriorly and medially. The bilateral contraction of the medial pterygoid elevates and protrudes the mandible, closing the mouth. This movement is crucial for the act of chewing, as it facilitates the grinding of food.
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The lateral pterygoid muscle
The primary function of the lateral pterygoid muscle is to control the function of the jaw and TMJ. It is the only muscle of mastication that participates in depressing the mandible and opening the jaw. It also protrudes the mandible by pulling the head of the condyle out of the mandibular fossa along the articular eminence. When contracting bilaterally, the lateral pterygoid muscle protrudes and depresses the mandible, and when contracting unilaterally, it rotates 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.
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The mandible's elevation, depression, protrusion, retraction and side-to-side movement
The mandible is a part of the jawbone and is connected to the skull at the temporomandibular joint (TMJ). The muscles of mastication are a group of muscles responsible for the movement of the mandible at the TMJ, which enables chewing, grinding food, and approximating the teeth. There are four main muscles of mastication: the masseter, temporalis, medial pterygoid, and lateral pterygoid. These muscles originate from the surface of the skull and attach onto the rami of the mandible at the TMJ.
The masseter muscle is a rectangularly shaped muscle with three layers: superficial, deep, and intermediate. It originates from the inferior zygomatic arch and the anterior two-thirds of the zygomatic arch, with a connection to the posterior aspect of the zygomatic bone. The major function of the masseter muscle is to elevate the mandible and approximate the teeth. The intermediate and deep muscle fibres of the masseter function to retract the mandible, while the superficial fibres function to protrude the mandible.
The temporalis muscle fibres converge inferiorly, forming a tendon that exits the temporal fossa, passing underneath the zygomatic arch, and inserting on the coronoid process of the mandible. The function of the anterior and mid fibres of the temporalis muscle is to elevate the mandible. The posterior fibres of the temporalis muscle function to retract the mandible. It also contributes to side-to-side grinding movement.
The medial pterygoid muscle is a thick rectangular muscle with a superficial head and a deep head. The deep head is larger than the superficial head. The medial pterygoid muscle fibres converge inferiorly, forming a tendon that inserts on the medial ramus of the mandible posterior and inferior to the mylohyoid groove of the mandible. 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 lateral pterygoid muscle is a short, thick muscle with two heads: the upper and lower heads. The upper head arises from the infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone, while the lower head arises from the lateral surface of the lateral pterygoid plate of the sphenoid bone. The lateral pterygoid muscle is the sole muscle of mastication responsible for causing depression of the mandible, although this is largely the result of gravity. It also assists with protrusion and side-to-side movement of the mandible.
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Frequently asked questions
The masseter, medial pterygoid, and temporalis muscles all contribute to the protrusion of the mandible.
The mandible is the only bone that moves during mastication and other activities, such as talking.
The muscles of mastication are a group of muscles associated with movements of the jaw. There are four muscles: the masseter, temporalis, medial pterygoid, and lateral pterygoid.
