Maximus Gage
The act of chewing, or mastication, involves the adduction and lateral motion of the jaw bone. There are four muscles that are primarily responsible for mastication: the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles. These muscles attach to the mandible, the only bone that moves during mastication, and produce movements of the lower jaw at the temporomandibular joint (TMJ) to enable functions such as chewing and grinding. In addition to these four muscles, other muscles also help with the process of mastication, such as those of the tongue and the cheeks.
| Characteristics | Values |
|---|---|
| Number of muscles | 4 |
| Muscle names | Temporalis, Masseter, Medial Pterygoid, Lateral Pterygoid |
| Muscle shape | Quadrangular, triangular, fan-shaped |
| Muscle movement | Elevation, depression, protrusion, retraction, side-to-side movement |
| Muscle function | Adduction of the mandible, abduction of the mandible, grinding food |
| Muscle origin | Surface of the skull |
| Muscle attachment | Rami of the mandible at the temporomandibular joint |
| Innervation | Motor branches of the mandibular division of the trigeminal nerve |
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What You'll Learn
- The masseter muscle helps elevate the mandible and approximate the teeth
- The buccinator, a facial expression muscle, keeps food in the oral cavity
- The temporalis muscle is involved in the retraction of the mandible
- The medial pterygoid muscle assists with elevation, protrusion and side-to-side motion of the mandible
- The lateral pterygoid muscle is the major protractor of the mandible
The masseter muscle helps elevate the mandible and approximate the teeth
The masseter muscle is one of the four muscles of mastication, which are the primary muscles involved in the chewing movement of the mandible at the temporomandibular joint (TMJ). The other three muscles of mastication are the temporalis, medial pterygoid, and lateral pterygoid muscles.
The masseter muscle is a strong, quadrangular muscle that covers the lateral aspect of the ramus of the mandible. It is composed of two layers: a larger, superficial layer and a deep layer. 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 helps to elevate the mandible and approximate the teeth. This means that it moves the mandible upwards and brings the teeth together or closes the mouth. The intermediate and deep muscle fibres of the masseter function to retract the mandible, pulling the jaw backwards, while the superficial fibres function to protrude the mandible, moving the jaw forwards.
The masseter muscle is supplied by the masseteric nerve, a branch of the mandibular nerve. Its blood supply is derived from the masseteric artery, which is a branch of the maxillary artery.
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The buccinator, a facial expression muscle, keeps food in the oral cavity
The buccinator muscle is a facial expression muscle that helps in mastication by keeping food in the oral cavity. It is one of 43 muscles that control our facial functions, and it forms the lateral wall of the oral cavity in mammals. This quadrilateral flat muscle is located deep under the skin and is mostly covered by the masseter and other facial muscles.
The buccinator muscle is innervated by the facial nerve and arises from the pterygomandibular raphe and the alveolar bone of the maxilla and mandible. It runs anteriorly to interdigitate with the fibres of the orbicularis oris in the corner of the mouth. The muscle is described as having predominantly horizontal fibres, with some sources also noting the presence of vertical fibres.
The primary role of the buccinator muscle is to control the bolus during mastication by keeping food between the tooth surfaces and preventing injury to the buccal mucosa. It does this by compressing the cheeks and thickening the entire cheek, acting as a muscular hydrostat. This thickening mechanism is believed to be how the cheek pushes food towards the tongue. The buccinator muscle also helps to prevent a person from biting their cheeks while eating.
In addition to its role in mastication, the buccinator muscle also controls airflow through the mouth, which is essential for whistling, sucking in or blowing out air, meditative breathing, and playing certain musical instruments. It also contributes to forming a person's smile, along with other facial expression muscles.
The masseter, medial pterygoid, lateral pterygoid, and temporalis muscles are the four main mastication muscles. They are attached to the skull and the lower jaw and are responsible for the movement of the jaw joint. However, other muscles like the buccinator and mylohyoid also play supporting roles in helping us eat and drink.
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The temporalis muscle is involved in the retraction of the mandible
The act of chewing, or mastication, involves the temporomandibular (TMJ) joint and a group of muscles that are responsible for the mandible's movement. These muscles of mastication develop from the first pharyngeal arch and are innervated by the third (mandibular) branch of the trigeminal nerve.
The temporalis muscle is one of the four muscles of mastication. It is a thin, fan-shaped muscle situated within the temporal fossa of the skull, which is a shallow depression on the lateral aspect of the skull. The temporalis muscle is covered by the temporal fascia, also known as the temporal aponeurosis, and can be seen and felt contracting when the jaw is clenching and unclenching.
The temporalis muscle is the primary retractor of the mandible. Its anterior portion moves the mandible dorsocranially (elevation), while its posterior fibres pull the mandible posteriorly (retraction). 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 upwards (elevation), and in unison, these actions facilitate the closing of the mouth and the approximation of the teeth.
The temporalis muscle is also involved in side-to-side movements of the jaw. The unilateral contraction of the temporalis muscle contributes to the grinding movement of the mandible, helping to enhance the process of eating.
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The medial pterygoid muscle assists with elevation, protrusion and side-to-side motion of the mandible
The act of chewing involves the movement of the mandible at the temporomandibular joint, also known as the TMJ. This movement is made possible by the muscles of mastication, four muscles that originate from the surface of the skull and attach to the mandible at the TMJ. These four muscles are the masseter, the temporalis, the medial pterygoid, and the lateral pterygoid.
The medial pterygoid muscle assists with elevation, protrusion, and side-to-side motion of the mandible. The muscle has two heads, the deep head and the superficial head. The superficial head originates from the maxillary tuberosity and the pyramidal process of the palatine bone. The medial pterygoid 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 bilateral contraction of the medial pterygoid muscle results in the elevation of the mandible, which closes the mouth. The muscle fibres are oriented in such a way that they also pull the mandible forward, resulting in protrusion. Additionally, the unilateral contraction of the medial pterygoid muscle, in conjunction with the lateral pterygoid muscle, causes the mandible to swing to the opposite side, enabling side-to-side motion. These movements facilitated by the medial pterygoid muscle are crucial for the act of chewing and grinding food.
The masseter muscle, another muscle of mastication, also contributes to the elevation of the mandible and the approximation of the teeth. The intermediate and deep muscle fibres of the masseter retract the mandible, while the superficial fibres protrude it. The masseter muscle is fan-shaped and fills the temporal fossa, with anterior fibres oriented vertically and posterior fibres oriented horizontally.
The lateral pterygoid muscle, the fourth muscle of mastication, is involved in protrusion, depression, and side-to-side movement of the mandible. It is a two-headed muscle with a smaller superior head and a larger inferior head. The lateral pterygoid muscle works in conjunction with the medial pterygoid muscle to facilitate the side-to-side motion of the mandible.
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The lateral pterygoid muscle is the major protractor of the mandible
The act of chewing involves the movement of the mandible at the temporomandibular joint, also known as the TMJ. This movement is facilitated by the muscles of mastication, of which there are four primary muscles. These muscles originate from the surface of the skull and attach to the mandible at the TMJ.
One of these four muscles is the lateral pterygoid muscle, which is the major protractor of the mandible. The lateral pterygoid muscle has a distinct triangular shape and consists of two heads: the superior head and the inferior head. The superior head arises from the greater wing of the sphenoid bone, specifically from its infratemporal surface and crest. On the other hand, the inferior head, which is larger, originates from the lateral surface of the lateral pterygoid plate of the sphenoid bone.
The fibres of the superior and inferior heads converge to form a tendon that attaches to the neck of the mandible, specifically inserting into the pterygoid fovea. This muscle is supplied by a branch of the anterior division of the mandibular nerve. The lateral pterygoid muscle is unique in that it is the only muscle of mastication that assists in depressing the mandible, or opening the jaw.
When the lateral pterygoid muscles work together bilaterally, they protrude and lower the mandible, pushing the jaw forward. This action is crucial for activities such as speaking, singing, and clenching. On the other hand, when the lateral pterygoid muscle acts unilaterally, it moves the mandible medially, resulting in a "side-to-side" movement of the jaw. This unilateral action is often performed in conjunction with the medial pterygoid muscles, which also play a significant role in mandibular movements.
In summary, the lateral pterygoid muscle, with its unique structure and functions, is the major protractor of the mandible. Its ability to facilitate protrusion, depression, and side-to-side movements of the mandible makes it an essential component of the chewing process and other oral functions.
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Frequently asked questions
The muscles that help you chew are known as the muscles of mastication. There are four main muscles: the temporalis, the masseter, the medial pterygoid, and the lateral pterygoid.
The masseter muscle is the most powerful muscle of mastication. It is responsible for elevating the mandible (closing the mouth) and approximating the teeth.
The lateral pterygoid muscle is the major protractor (opener) of the jaw. It is responsible for side-to-side movement of the jaw during chewing.
The medial pterygoid muscle assists with the elevation and protrusion of the mandible. It also assists the lateral pterygoid muscle with side-to-side mandibular motion, helping with the grinding of food.
