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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 joint (TMJ). The four main muscles of mastication are the masseter, temporalis, medial pterygoid, and lateral pterygoid. This paragraph will focus on the muscles responsible for depressing the mandible.
| Characteristics | Values |
|---|---|
| Muscles responsible for depressing the mandible | Lateral pterygoid, temporalis, medial pterygoid, masseter, platysma, suprahyoid, and infrahyoid |
| Origin of the lateral pterygoid muscle | Inferior temporal surface of the greater wing of the sphenoid bone |
| Lateral pterygoid muscle fibre orientation | Horizontal |
| Shape of the lateral pterygoid muscle | Triangular |
| Number of heads of the lateral pterygoid muscle | Two |
| Origin of the temporalis muscle | Temporal fossa to the inferior temporal line of the lateral skull |
| Shape of the temporalis muscle | Fan-shaped |
| Number of heads of the temporalis muscle | One |
| Origin of the medial pterygoid muscle | Maxillary tuberosity of the inferior maxilla |
| Shape of the medial pterygoid muscle | Thick rectangular |
| Number of heads of the medial pterygoid muscle | Two |
| Origin of the masseter muscle | Inferior zygomatic arch and anterior two-thirds of the zygomatic arch |
| Shape of the masseter muscle | Rectangular |
| Number of layers of the masseter muscle | Three (superficial, deep, and intermediate) |
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What You'll Learn
- The lateral pterygoid muscle is the primary depressor of the mandible
- The suprahyoid muscle group also depresses the mandible
- The masseter muscle elevates and retracts the mandible
- The temporalis muscle elevates and retracts the mandible
- The medial pterygoid muscle assists with the mandible's protrusion and elevation
The lateral pterygoid muscle is the primary depressor of the mandible
The lateral pterygoid muscle is the primary muscle responsible for the depression of the mandible. This muscle is one of the four muscles of mastication, which are a group of muscles associated with movements of the jaw. The other three muscles are the masseter, temporalis, and medial pterygoid.
The lateral pterygoid muscle has a unique triangular shape with two distinct heads: the superior head and the inferior head. The superior head originates from the greater wing of the sphenoid bone, specifically its infratemporal surface and crest. On the other hand, the inferior head arises from the lateral surface of the lateral pterygoid plate of the sphenoid bone.
The fibres from these two heads merge and run posterolaterally, forming a tendon that inserts into a shallow depression on the anterior aspect of the neck of the mandible. This depression is known as the pterygoid fovea, and it is located on the condylar process of the mandible. Additionally, some fibres from the lateral pterygoid muscle insert into the joint capsule and articular disc of the temporomandibular joint (TMJ).
The function of the lateral pterygoid muscle is not limited to depressing the mandible. It also plays a role in protrusion and side-to-side movement of the mandible. The degree of contraction of the muscle determines its function. For instance, bilateral contraction of the lateral pterygoid muscles results in protrusion and depression of the mandible, while unilateral contraction on one side, along with the ipsilateral medial pterygoid muscle, moves the mandible to the opposite side.
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The suprahyoid muscle group also depresses the mandible
The suprahyoid muscle group is made up of the digastric muscle, mylohyoid muscle, and geniohyoid muscle. The stylohyoid muscle is also considered a part of the suprahyoid muscle group by some sources. These muscles are located superior to the hyoid bone, attaching it to the mandible, the tongue, and the skull. They also form the floor of the oral cavity.
The suprahyoid muscles are responsible for positioning the hyoid bone and coordinating the movements of the floor of the mouth and the hyoid bone during swallowing or vocalization. They also play a role in chewing and speaking. When the hyoid bone is fixed, the suprahyoid muscles depress the mandible.
The hyoid bone is the only bone in the body that is not connected to any other bone. Its position is determined by the suprahyoid and infrahyoid muscles. When the hyoid bone is fixed, the suprahyoid muscles are responsible for mandibular depression and retrusion of the mandible during the opening of the mouth. The geniohyoid muscle assists with depressing the mandible and pulling it inwards.
The lateral pterygoid muscle is the sole muscle of mastication that causes depression of the mandible. However, the suprahyoid muscles also depress the mandible against resistance when the infrahyoid muscles fix or depress the hyoid bone.
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The masseter muscle elevates and retracts the mandible
The masseter muscle is one of the four muscles responsible for mastication (chewing). It is a powerful, fan-shaped, superficial quadrangular muscle with two layers: superficial and deep. The superficial layer arises from the maxillary process of the zygomatic bone and the anterior two-thirds of the zygomatic arch. The deep layer arises from the medial surface and inferior margin of the zygomatic arch.
The masseter muscle is primarily responsible for the elevation of the mandible and some protraction of the mandible. The intermediate and deep muscle fibres of the masseter function to retract the mandible, and the superficial fibres function to protrude the mandible. The deep fibres are important stabilisers of the temporomandibular joint (TMJ). When the masseter contracts, it causes powerful elevation of the mandible, causing the mouth to close. The masseter reflex, also known as the mandibular reflex or jaw-jerk reflex, involves opening the mouth and placing a finger on the chin of the patient and striking the finger with a reflex hammer. The downward force can cause a reflex action in the masseter muscles, resulting in an elevation of the mandible.
The temporalis muscle, on the other hand, functions mainly as an elevator of the mandible, opposing gravity when the mouth is closed. The contraction of the posterior, more horizontal fibres of the muscle produces a retraction of the mandible, pulling the jaw backwards.
The lateral pterygoid muscle is the sole muscle of mastication that causes depression of the mandible, along with protrusion and side-to-side movement of the mandible. The medial pterygoid muscle assists with elevation and protrusion of the mandible and assists the lateral pterygoid muscle with side-to-side mandibular motion to help with the grinding of food.
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The temporalis muscle elevates and retracts the mandible
The temporalis muscle is a fan-shaped muscle with anterior fibres that have a vertical orientation, mid fibres with an oblique orientation, and posterior fibres that have a horizontal orientation. It is the strongest muscle of the temporomandibular joint and the primary retractor of the mandible. The temporalis muscle facilitates the movement of the mandible at the temporomandibular joint, which enhances the act of mastication (chewing).
The anterior fibres of the temporalis muscle run inferiorly in a vertical direction, while the posterior fibres are directed horizontally. Both anterior and posterior fibres converge onto a tendon that runs medial to the zygomatic arch. The tendon inserts onto the apex and medial surface of the coronoid process of the mandible. The contraction of the anterior fibres of the temporalis muscle moves the mandible dorsocranially, resulting in its elevation. On the other hand, the contraction of the posterior fibres produces a backward movement of the mandible, leading to its retraction.
The temporalis muscle also contributes to side-to-side grinding movements of the mandible. The unilateral contraction of the temporalis muscle is essential for these alternating mandibular motions during chewing. In addition to its role in mastication, the temporalis muscle, along with other muscles of mastication, helps to approximate or bring together the teeth.
Other muscles, such as the medial pterygoid, lateral pterygoid, and masseter muscles, also play a role in mandibular movements. The medial pterygoid and masseter muscles assist with the elevation of the mandible, while the lateral pterygoid muscle is the sole muscle responsible for depressing or lowering the mandible, often with the assistance of gravity. These muscles, along with the temporalis muscle, work together to enable the complex movements of the mandible during chewing, grinding, and speaking.
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The medial pterygoid muscle assists with the mandible's protrusion and elevation
The mandible, or jawbone, is the only bone in the body that moves during mastication (chewing) and other activities like talking. The medial pterygoid muscle is one of the muscles responsible for the movement of the mandible. This muscle is innervated by the medial pterygoid branch of the mandibular division of the trigeminal nerve (CN V3). It receives its blood supply from the pterygoid branches of the maxillary artery.
The medial pterygoid muscle assists with the elevation and protrusion of the mandible. It is a major elevator of the jaw and is involved in pulling the mandible forward. The bilateral contraction of this muscle elevates the mandible and closes the mouth. The unilateral contraction of the medial pterygoid, together with the lateral pterygoid, causes the mandible to swing to the opposite side. These movements are crucial for the act of chewing, allowing for side-to-side movements.
The medial pterygoid muscle also has a role in the horizontal movements of the jaw. It assists the lateral pterygoid muscle with side-to-side mandibular motion, which is important for grinding food during the chewing process. The lateral pterygoid muscle is the only muscle of mastication that assists in depressing the mandible (opening the jaw). It is a short, two-headed muscle located in the infratemporal fossa of the skull. The fibres from both heads merge and insert on the pterygoid fovea on the neck of the mandible.
The masseter muscle is also involved in the movement of the mandible. It is a fan-shaped muscle that fills the temporal fossa. The deep fibres of the masseter muscle function to retract the mandible, while the superficial fibres protrude the mandible. The temporalis muscle is another elevator of the mandible, opposing gravity when the mouth is closed. The contraction of its posterior fibres produces a retraction of the mandible, pulling the jaw backwards.
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Frequently asked questions
The lateral pterygoid muscle is the primary muscle responsible for depressing the mandible. The suprahyoid muscle group, which includes the digastric, mylohyoid, and geniohyoid muscles, also depresses the mandible against resistance.
The lateral pterygoid muscle is a triangular muscle with two heads: the superior head and the inferior head. It functions to depress and protrude the mandible, as well as assist with side-to-side mandibular motion during chewing and grinding of food.
The muscles of mastication are a group of muscles responsible for the movement of the mandible, or jaw. There are four main muscles of mastication: masseter, temporalis, medial pterygoid, and lateral pterygoid. These muscles work together to produce movements such as elevation, depression, protrusion, retraction, and side-to-side motion during chewing and grinding food.
