Dominic Stone
The mandible is the only bone that moves during mastication (chewing) and other activities, such as talking. The muscles that close the mandible are the masseter, temporalis, and medial pterygoid. These muscles are part of the muscles of mastication, a group of muscles associated with movements of the jaw. The lateral pterygoid muscle is responsible for opening the mandible.
| Characteristics | Values |
|---|---|
| Muscles responsible for closing the mandible | Masseter, Temporalis, Medial Pterygoid |
| Number of muscles of mastication | 4 |
| Origin of Temporalis muscle | Temporal fossa to the inferior temporal line of the lateral skull |
| Temporalis muscle nerve | Deep temporal nerve |
| Temporalis muscle blood supply | Deep temporal part of the maxillary artery, Middle temporal branches of the superficial temporal artery |
| Function of anterior and mid fibres of the Temporalis muscle | Elevate the mandible |
| Function of posterior fibres of the Temporalis muscle | Retract the mandible |
| Medial Pterygoid muscle shape | Thick rectangular with a superficial and deep head |
| Medial Pterygoid muscle nerve | Branch of the main trunk of the mandibular nerve |
| Medial Pterygoid muscle blood supply | Pterygoid branch of the 2nd part of the maxillary artery |
| Function of the Medial Pterygoid muscle | Assist with elevation, protrusion, and lateral movement of the mandible |
| Lateral Pterygoid muscle shape | Triangular with two heads |
| Lateral Pterygoid muscle function | Opening, deviation to either side, and anterior movement of the jaw |
| Masseter muscle shape | Rectangular with three layers (superficial, deep, and intermediate) |
| Masseter muscle nerve | Mandibular division of the Trigeminal Nerve |
| Masseter muscle blood supply | Masseteric artery |
| Function of the Masseter muscle | Elevate the mandible, approximate the teeth, retract the mandible, and assist with protrusion |
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What You'll Learn
The masseter muscle
The masseter is one of the four muscles of mastication, which is a group of muscles responsible for the chewing movement of the mandible at the temporomandibular (TMJ) joint. The other three muscles of mastication are the temporalis, medial pterygoid, and lateral pterygoid. The masseter is a powerful, thick, and rectangular muscle with two divisions: superficial and deep. The superficial portion of the masseter muscle originates from the temporal process of the zygomatic bone and arch. The deep portion of the masseter muscle originates from the entire surface of the zygomatic arch. The fibres of the superficial portion pass inferior-posteriorly over the deep portion and insert onto the angle of the mandible and the inferior portion of the lateral surface of the mandibular ramus.
The word "masseter" originates from the Greek word "μασᾶσθαι" ("masasthai"), which means "to chew." The masseter muscle's positioning is a distinguishing feature of hystricognathous creatures, such as mole-rats, where it passes partially through the infraorbital foramen and connects to the bone on the opposite side.
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The temporalis muscle
The anterior and mid fibres of the temporalis muscle elevate the mandible, while the posterior fibres retract the mandible. Together, these actions facilitate the closing of the mouth and the approximation of the teeth. The unilateral contraction of the temporalis muscle contributes to 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 the mandible (closing the mouth), protruding the mandible, and assisting with mastication (chewing). The unilateral contraction of the medial pterygoid causes rotation of the mandible, while bilateral contraction elevates and protrudes it.
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The lateral pterygoid muscle
The inferior head originates from the lateral surface of the lateral pterygoid plate of the sphenoid bone, while the superior head originates from the greater wing of the sphenoid. 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 TMJ. The inferior fibers insert into the pterygoid fovea on the neck of the condyloid process of the mandible.
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How the muscles work together
The mandible is the only bone that moves during mastication (chewing) and other activities like talking. The muscles of mastication are a group of muscles responsible for the chewing movement of the mandible at the temporomandibular (TMJ) joint. These muscles enhance the process of eating and assist in grinding food. They also function to approximate the teeth.
The four main muscles of mastication are 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 movement performed by these muscles are elevation, depression, protrusion, retraction, and side-to-side movement. Three out of the four main muscles are responsible for adduction (closing) of the mandible, while one helps in the abduction (opening) of the mandible.
The masseter muscle is a strong, quadrangular muscle with three layers: superficial, deep, and intermediate. Its major function is to elevate the mandible, with a minor contribution to protrusion. The deep and intermediate muscle fibres of the masseter function to retract the mandible, while the superficial fibres function to protrude it. The deep fibres also help to stabilise the TMJ.
The temporalis muscle is fan-shaped and functions mainly as an elevator of the mandible. The contraction of the posterior, more horizontal fibres of the muscle produces a retraction of the mandible, pulling the jaw backwards. The temporalis muscle also contributes to grinding movements by moving the mandible from side to side.
The medial pterygoid muscle is quadrangular and has two heads: deep and superficial. It assists with elevation and protrusion of the mandible. It also helps the lateral pterygoid muscle with side-to-side mandibular motion during the grinding of food.
The lateral pterygoid muscle is triangular and has two heads: superior and inferior. It is the primary muscle responsible for the depression of the mandible. It also assists with protrusion and side-to-side movement.
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Frequently asked questions
The masseter, temporalis, and medial pterygoid muscles are responsible for closing the mandible.
The temporalis muscle is fan-shaped.
The medial pterygoid muscle assists with the elevation, protrusion, and lateral movement of the mandible.
