Logan Steele
The human jaw, or mandible, is controlled by several muscles that enable essential functions such as chewing, talking, and even beginning the digestion process. These muscles include the masseter, temporalis, medial pterygoid, and lateral pterygoid, each playing a specific role in the movement of the jaw. The masseter, the most powerful muscle of mastication, elevates the jaw, closing the mouth. The temporalis, a fan-shaped muscle, also elevates and retracts the jaw, while the lateral pterygoid is the only muscle that actively opens the jaw. These muscles work in synchronisation to produce the side-to-side rocking motion associated with chewing and grinding food.
| Characteristics | Values |
|---|---|
| Main muscles that control the jaw | Masseter, Temporalis, Internal and External Pterygoids, Supra and Infra-Hyoid |
| Function of the Masseter muscle | Raises the lower jaw, assists in mastication, jaw closure |
| Function of the Temporalis muscle | Elevates and retracts the jaw, assists in side-to-side movement |
| Function of the Lateral Pterygoid | Opens the jaw, produces lateral movement in the jaw |
| Function of the Medial Pterygoid | Elevates and closes the jaw, assists in protrusion of the mandible and mastication |
| Function of the Digastric muscle | Opens the mouth, depresses the mandible |
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What You'll Learn
The masseter muscle
The word "masseter" comes from the Greek "μασᾶσθαι" ("masasthai"), which means "to chew", reflecting the muscle's important role in the chewing process.
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The temporalis muscle
The middle fibres of the temporalis muscle run in an oblique direction towards the inferior and anterior. They are used for both the elevation and retraction of the mandible. Additionally, the unilateral contraction of the middle fibres provokes the lateral movement of the mandible. The temporalis muscle is derived from the first pharyngeal arch during development.
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The lateral pterygoid muscle
The primary function of the lateral pterygoid muscle is to control the movement of the mandible, particularly during mastication and mandibular movements. It assists in protruding the mandible forward and depressing it downward, as well as mediotrusion, which is the movement of the mandibular condyle towards the midline. The unilateral action of the lateral pterygoid muscle results in lateral mandibular movement to the contralateral side, while the bilateral contraction of the muscle leads to the forward movement of the mandible.
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The medial pterygoid muscle
The primary function of the medial pterygoid muscle is to produce movements of the mandible at the temporomandibular joint. The bilateral contraction of this muscle elevates the mandible and closes the mouth. Unilateral contraction of the medial pterygoid causes rotation of the mandible, while bilateral contraction also protrudes it. These movements are crucial for the act of chewing.
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The digastric muscle
The two bellies of the digastric muscle have different embryological origins and are supplied by different cranial nerves. The anterior belly is derived from the first pharyngeal arch, while the posterior belly arises from the mastoid notch on the inferior surface of the skull. The mastoid notch is a deep groove between the mastoid process and the styloid process. The anterior belly is innervated by the nerve to the mylohyoid muscle, a branch of the inferior alveolar nerve that arises from the mandibular nerve. The posterior belly, on the other hand, is supplied by the digastric branch of the facial nerve.
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Frequently asked questions
The masseter, temporalis, medial pterygoid, and superior head of the lateral pterygoid are the jaw-closing muscles. The masseter is the most powerful muscle of mastication.
The anterior digastric, mylohyoid, and inferior head of the lateral pterygoid are the jaw-opening muscles. The lateral pterygoid is the only muscle of mastication that actively opens the jaw.
The masseter is a large muscle that raises the lower jaw and assists in mastication. It connects the jaw to the cheekbone and is the prime mover of jaw closure.
