Dominic Stone
The muscles of mastication are a group of muscles that enable chewing and grinding movements of the jaw. The four main muscles of mastication are the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles. These muscles attach to the mandible and facilitate movements such as protrusion, retraction, elevation, depression, and side-to-side rotation. The masseter muscle, for instance, elevates the mandible and approximates the teeth, while the lateral pterygoid muscle depresses the mandible and assists with protrusion and side-to-side movement. These muscles are innervated by the mandibular nerve, which is a branch of the trigeminal nerve.
| Characteristics | Values |
|---|---|
| Number of muscles | 4 |
| Names of muscles | Temporalis, Medial Pterygoid, Lateral Pterygoid, Masseter |
| Muscle shape | Fan-shaped, rectangular, triangular |
| Muscle fibres | Vertical, oblique, horizontal |
| Muscle movement | Elevation, depression, protrusion, retraction, side-to-side |
| Muscle function | Chewing, grinding food, approximating teeth |
| Innervation | Mandibular nerve (V3), Trigeminal nerve (CN V) |
| Blood supply | Masseteric artery, Maxillary artery |
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What You'll Learn
The four main muscles used for chewing
The first of these four muscles is the temporalis muscle, which is situated in the temporal fossa. This muscle is responsible for elevating the mandible and closing the mouth. It also assists in side-to-side movement of the mandible.
The second muscle is the medial pterygoid, which is located in the infratemporal fossa. This muscle is involved in protrusion, or protraction, of the mandible, moving it forwards. It also assists in side-to-side movement when working in conjunction with the lateral pterygoid muscle.
The third muscle is the lateral pterygoid, which is also found in the infratemporal fossa. This muscle is responsible for depressing the mandible and opening the mouth. It also assists with protrusion and side-to-side movement.
The fourth muscle is the masseter muscle, which is located in the cheek area. This muscle helps to elevate the mandible and approximate, or close, the teeth. The deep muscle fibres of the masseter also assist in retracting the mandible, while the superficial fibres help to protrude it.
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The function of the lateral pterygoid
The lateral pterygoid muscle is a craniomandibular muscle that helps control movement of the temporomandibular joint (TMJ). It is one of the four muscles of mastication, along with the medial pterygoid, temporalis, and masseter muscles. These muscles attach to the mandible and produce movements of the lower jaw, enabling functions such as chewing and grinding.
The lateral pterygoid muscle has two heads, superior and inferior, with the inferior head being much wider than the superior one. The superior head originates from the infratemporal surface of the greater wing of the sphenoid bone, while the inferior head originates from the lateral surface of the lateral pterygoid plate of the sphenoid bone. The fibres from both heads merge and insert onto a shallow depression on the anterior aspect of the neck of the mandible called the pterygoid fovea.
The lateral pterygoid muscle is innervated by the lateral pterygoid nerve, a branch of the mandibular nerve (CN V3). Its blood supply is derived from the pterygoid branch of the maxillary artery. The understanding of the anatomy and function of the lateral pterygoid muscle is crucial for comprehending the mechanics of chewing and maintaining oral health.
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The role of the masseter muscle
The masseter muscle is one of the four main muscles of mastication (chewing). It is a strong, thick, rectangular-shaped muscle in your face and jaw, with three distinct layers: the superficial, intermediate, and deep layers. The muscle fibres originate from the zygomatic arch of your skull (cheekbone) and extend down to the mandibular angle.
The masseter muscle has several important functions. Firstly, it is responsible for elevating the mandible (raising the lower jaw) during jaw closure. This elevation occurs through the contraction of the superficial fibres of the muscle. The masseter muscle also assists in the protrusion of the mandible, which is partly caused by the strength of its superficial fibres. In addition, the deep fibres of the masseter muscle play a role in retracting the mandible and stabilising the temporomandibular joint (TMJ).
The masseter muscle works together with the other muscles of mastication, which include the temporal muscle, lateral pterygoid muscle, and medial pterygoid muscle. These muscles attach to the rami of the mandible at the TMJ and enable the movement of the jaw during chewing. The cardinal mandibular movements of mastication are elevation, depression, protrusion, retraction, and side-to-side motion. These movements enhance the process of eating by assisting in the grinding of food.
In summary, the masseter muscle is a crucial muscle for chewing and plays a significant role in jaw function and stability. Its contraction helps to elevate and protrude the mandible, while its deep fibres contribute to retraction and stabilisation of the TMJ.
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The temporalis muscle
The anterior portion of the temporalis muscle moves the mandible dorsocranially (elevation) while its posterior fibres pull the mandible posteriorly (retrusion). The contraction of the posterior fibres of the temporalis muscle results in the backward movement of the mandible (retrusion). The contraction of its anterior fibres moves the mandible dorsocranially (elevation). In unison, these actions facilitate the closing of the mouth and the approximation of the teeth.
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The medial pterygoid
Unilateral contraction of the medial pterygoid muscle causes a slight medial rotation of the mandible. When this occurs simultaneously with the contraction of the ipsilateral lateral pterygoid, it results in a noticeable movement where the same-sided part of the mandible swings anteriorly and medially. Bilateral contraction of the medial pterygoid muscles pushes the mandible forward, protruding the mandible.
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Frequently asked questions
The four main muscles used for chewing are the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles.
The functions of these muscles include elevation, depression, protrusion, retraction, and side-to-side movement of the mandible.
The medial pterygoid muscle is involved in the protrusion of the mandible. It also works with the lateral pterygoid muscle to enable side-to-side movement.
