Logan Steele
The mandible, or lower jaw, is the only bone in the face that moves. It is connected to the temporal bone of the skull via the temporomandibular joint, which allows movement in all planes. The mandible can be elevated, retracted, protracted, or depressed. The muscles that produce these movements are the masseter, the temporalis, and the pterygoid muscles. The masseter muscle is the most powerful muscle of mastication, elevating the mandible. The temporalis muscle, a broad muscle that fans out over the temporal bone, is responsible for retracting the mandible.
| Characteristics | Values |
|---|---|
| Muscle that retracts the mandible | Temporalis |
| Location of the temporalis muscle | Temporal fossa |
| Shape of the temporalis muscle | Fan-shaped |
| Other muscles that act on the mandible | Masseter, Lateral pterygoid, Digastric, Mylohyoid, Geniohyoid |
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What You'll Learn
The temporalis muscle
Tension in the temporalis muscle can induce pain in the temporal area and is likely to be involved in jaw pain and headaches. Bruxism, or the habitual grinding of teeth, and clenching of the jaw can lead to overwork of the muscle and result in pain. A myotendinous rupture of the muscle can occur during a seizure due to extreme clenching of the jaw.
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The masseter muscle
The word "masseter" comes from the Greek "μασᾶσθαι" ("masasthai"), meaning "to chew". The masseter muscle's positioning is a distinguishing feature of hystricognathous creatures, such as mole-rats, and it also provides the tissue for acoustic fat bodies in toothed whales, which use them for echolocation.
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The pterygoid muscles
The lateral pterygoid is a short, two-headed, fan-shaped muscle located in the infratemporal fossa of the skull. The smaller superior head arises from the infratemporal crest of the greater wing of the sphenoid bone, while the larger inferior head arises from the lateral surface of the lateral pterygoid plate. 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. The lateral pterygoid contributes to the function of protruding and depressing the mandible when contracting bilaterally, and by rotating the mandible when contracting unilaterally.
The medial pterygoid muscle is a thick quadrilateral muscle that arises by two heads, a superficial and a deep head. The smaller superficial head originates from the maxillary tuberosity and pyramidal process of the palatine bone. The larger deep head originates from the medial surface of the lateral plate of the pterygoid process and the pyramidal process of the palatine bone. From their origin, the muscle fibres run posteroinferiorly and laterally, surrounding the lower fibres of the lateral pterygoid muscle. Together, the two heads of the medial pterygoid muscle insert onto the triangular impression located on the medial surface of the mandible. The medial pterygoid muscle has functions including elevating the mandible (closing the mouth), protruding the mandible, mastication (especially when the maxillary teeth and the mandibular teeth are close together), and excursing the mandible (contralateral excursion occurs with unilateral contraction).
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The mandible's four movements
The mandible is the only bone that moves during mastication (chewing) and other activities, such as talking. The movements of the mandible are facilitated by the temporomandibular joint (TMJ), which connects the mandible to the temporal bone. The TMJ is a synovial, condylar and hinge-type joint that allows for a combination of rotational and translational movements.
There are four important movements of the mandible: retraction, protrusion, elevation, and depression. Retraction refers to the movement of the mandible in a posterior direction, while protrusion is the movement in an anterior direction. Elevation involves bringing the mandible upwards in a superior direction, and depression brings the mandible in an inferior direction.
These movements are made possible by the muscles of mastication, which include the temporalis, masseter, medial pterygoid, and lateral pterygoid. The temporalis muscle, a large fan-shaped muscle in the temporal fossa, is responsible for elevating and retracting the mandible. The masseter, originating from the zygomatic arch, also elevates and retracts the mandible. The pterygoid muscles, originating from the pterygoid process of the sphenoid bone, lie beneath the mandible and insert onto its medial surface.
The TMJ enables the mandible to perform complex movements through rotation and translation. Rotation occurs within the inferior cavity of the joint, between the superior surface of the condyle and the inferior surface of the articular disc. Translation, on the other hand, involves the movement of the articular disc within the superior cavity of the joint. During most normal movements, the mandible exhibits both rotation and translation simultaneously, resulting in intricate and challenging-to-visualize motions.
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The muscles of mastication
The temporalis muscle is a fan-shaped muscle that sits in the temporal fossa and inserts onto the coronoid process of the mandible. It elevates and retracts the mandible. The origin of the muscle spans from the temporal fossa to the inferior temporal line of the lateral skull. The fibres of the temporalis converge inferiorly, forming a tendon that exits the temporal fossa, passing underneath the zygomatic arch and inserting on the mandible.
The masseter muscle is the most powerful muscle of mastication. It has two parts: deep and superficial. It originates on the zygomatic arch and inserts onto the lateral aspect of the lateral surface of the ramus of the mandible. The masseter elevates the mandible and approximates the teeth.
The medial pterygoid muscle has a quadrangular shape with two heads: deep and superficial. It is located inferiorly to the lateral pterygoid. The medial pterygoid receives innervation from the medial pterygoid nerve, a division of the mandibular nerve.
The lateral pterygoid muscle has a triangular shape with two heads: superior and inferior. It has horizontally oriented muscle fibres, making it the major protractor of the mandible. 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. The lateral pterygoid is the sole muscle of mastication that causes 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 temporalis muscle, a broad muscle that fans out to cover the temporal bone on the side of the skull, retracts the mandible.
The temporalis muscle sits in the temporal fossa and inserts into the coronoid process of the mandible.
The temporalis muscle is fan-shaped.
Place your fingers in the temple region on your face and clench your muscles as if you're chewing. You should be able to feel the muscle working.
