Logan Steele
The mandible is the only bone that moves during mastication (chewing) and other activities such as talking. The muscles of mastication are divided into jaw-openers (mandible depressors) and jaw-closers (mandible elevators). The lateral pterygoid muscle is the only muscle that depresses the mandible, causing it to open. The medial pterygoid muscle assists with the elevation and protrusion of the mandible.
| Characteristics | Values |
|---|---|
| Muscles that depress the mandible | Lateral pterygoid, Anterior digastric, Mylohyoid, Inferior head of the lateral pterygoid |
| Muscles that elevate the mandible | Masseter, Temporalis, Medial pterygoid, Superior head of the lateral pterygoid |
| Function of the lateral pterygoid muscle | Depression of the mandible, Protrusion, Side to side movement of the mandible |
| Function of the medial pterygoid muscle | Elevation, Protrusion, Side to side movement of the mandible |
| Function of the masseter muscle | Elevation of the mandible, Approximation of the teeth |
| Function of the temporalis muscle | Elevation of the mandible |
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What You'll Learn
Muscles that depress the mandible
The muscles of mastication are a group of muscles responsible for the chewing movement of the mandible at the temporomandibular joint (TMJ). They enhance the process of eating by assisting in grinding food and also function to approximate the teeth. The mandible is the only bone that moves during mastication and other activities, such as talking.
The muscles of mastication can be divided into jaw-openers (mandible depressors) and jaw-closers (mandible elevators). Muscles that depress the mandible and thus open the jaw include the anterior digastric, mylohyoid, and inferior head of the lateral pterygoid. The lateral pterygoid is the only muscle that also depresses, or opens, the jaw. The lateral and medial pterygoids work together to facilitate contralateral movement of the jaw, which allows for mastication. The lateral pterygoid also assists with protrusion and side-to-side movement of the mandible.
The suprahyoid muscle group is made up of the digastric muscle, mylohyoid muscle, and geniohyoid muscle. They depress the mandible against resistance when infrahyoid muscles fix or depress the hyoid bone. They are made up of the omohyoid, sternohyoid, sternothyroid, and thyrohyoid.
The muscles that elevate the mandible (close the mouth) include the masseter, temporalis, medial pterygoid, and superior head of the lateral pterygoid. The major function of the masseter muscle is to elevate the mandible, approximate the teeth, and provide protrusion and retraction of the mandible. The medial pterygoid muscle functions to assist with elevation and protrusion of the mandible. It also assists the lateral pterygoid muscle with side-to-side mandibular motion to help with the grinding of food.
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Muscles that elevate the mandible
The muscles of mastication, or masticatory muscles, are a group of muscles that enable the movement of the lower jaw at the temporomandibular joint (TMJ). These muscles can be divided into two groups: the primary (main) and secondary (accessory) muscles of mastication. The primary muscles of mastication include the temporalis, masseter, medial pterygoid, and lateral pterygoid muscles.
The temporalis muscle is a large, flat muscle that lies within the temporal fossa of the skull. It functions as an elevator of the mandible, with its anterior vertical fibres continually in action, opposing gravity when the mouth is closed. The masseter muscle also has a major function in elevating the mandible, with a minor contribution to protrusion (forward movement) of the mandible.
The medial pterygoid muscle is situated in the infratemporal fossa and has two heads with two sets of origins. Its principal functions are the elevation of the mandible and side-to-side movements when grinding and chewing. The lateral pterygoid muscle, specifically its superior head, also contributes to elevating the mandible.
Overall, these muscles work together to enable functions such as chewing and grinding by elevating the mandible and closing the mouth. They receive their innervation from the mandibular nerve and its branches, while their blood supply is derived from branches of the maxillary artery.
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Protrusion and retraction of the mandible
The mandible is the only bone that moves during mastication 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 (TMJ) joint. They enhance the process of eating and assist in grinding food. The four main muscles of mastication originate from the surface of the skull and attach onto the rami of the mandible at the TMJ. The movement performed by these muscles includes elevation, depression, protrusion, retraction, and side-to-side movement.
Protrusion, or protraction, moves the mandible forward. The superficial masseter and the masseter muscle, a powerful, superficial quadrangular muscle, contribute to protrusion. The medial pterygoid muscle also assists with protrusion. The superficial fibres of the intermediate and deep masseter fibres function to protrude the mandible.
Retraction pulls the mandible backward. The posterior fibres of the temporalis muscle function to retract the mandible. The contraction of the posterior, more horizontal fibres of the temporalis muscle produces a retraction of the mandible, pulling the jaw backward. The deep fibres of the masseter are important stabilisers of the TMJ.
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Side-to-side movement of the mandible
The mandible, which holds the lower teeth, comprises most of the lower third of the maxillofacial skeleton. The muscles of mastication are a group of muscles that enable the chewing movement of the mandible at the temporomandibular joint (TMJ). The TMJ is the junction of the mandible and the temporal bone. The four main muscles of mastication originate from the surface of the skull and attach to the rami of the mandible at the TMJ.
The mandible moves laterally during mastication. The side that the mandible is moving toward is the working side, and the condyle on that side moves upward and rearward. The amount of lateral movement in the condyle is referred to as the Bennett movement. The Bennett angle is the difference between a sagittal plane established through the condyle at rest and a line through the lateral movement's non-working condyle. The average Bennett angle is 7.5 degrees.
The posterior fibres of the temporalis muscle contribute to side-to-side grinding movement. The medial pterygoid muscle is a thick, rectangular muscle with a superficial head and a deep head. The medial pterygoid fibres converge inferiorly, forming a tendon that inserts on the medial ramus of the mandible. The insertion of the medial pterygoid forms a tendinous band with the insertion of the masseter, called the pterygoid-masseteric sling. The lateral pterygoid muscle is the sole muscle of mastication that causes depression of the mandible. It also assists with protrusion and side-to-side movement of the mandible.
The temporomandibular joint allows for complex mandibular movements, including side-to-side movement. The mandible rotates forward during opening. The temporomandibular joint is a synovial joint, with an upper and lower compartment divided by an intra-capsular disc. The muscles of mastication contribute to the mandible's complex movements and include the temporalis, masseter, medial pterygoid, and lateral pterygoid.
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The role of the temporomandibular joint
The temporomandibular joint (TMJ) is a hinge-type synovial joint that connects the mandible to the rest of the skull. It is formed by the union of the temporal bone cavity with the mandibular condyle, specifically the mandibular fossa and articular tubercle of the temporal bone, and the condylar process of the mandible. The TMJ is a complex joint that allows for a wide range of movements, including translational movements (protrusion, retraction, and lateral deviation) and rotational movements (elevation and depression).
The TMJ is composed of a synovial cavity, articular cartilage, and a capsule that covers the joint. The capsule is a fibrous membrane that surrounds the joint and attaches to the articular eminence, the articular disc, and the neck of the mandibular condyle. The articular disc, composed of fibrocartilage, runs between the two articular surfaces of the TMJ, dividing it into two compartments: the superior and inferior compartments. The superior compartment is bounded by the articular disc and the inferior compartment by the condyle of the mandible.
The articular disc plays a crucial role in stabilising the condyle of the mandible, reducing friction between the articular surfaces, and aiding in joint lubrication. The two compartments of the TMJ have distinct functions in terms of movements. The superior compartment is lined by the superior synovial membrane, while the inferior compartment is lined by the inferior synovial membrane, which has an average synovial fluid volume of 0.9 mL.
The TMJ is supplied by three main arteries: the deep auricular artery, the superficial temporal artery, and the anterior tympanic artery. Venous drainage occurs through the superficial temporal vein and the maxillary vein. Innervation to the TMJ is provided by branches from the mandibular division of the trigeminal nerve, primarily through the auriculotemporal branch, along with contributions from the masseteric and deep temporal nerves.
The TMJ plays a vital role in the stomatognathic system, working in synergy with various anatomical structures to enable essential functions such as opening the mouth, swallowing, breathing, phonation, sucking, and facial expressions. Disorders of the TMJ, known as temporomandibular disorders (TMD), can cause significant pain and are often treated with non-invasive, non-surgical approaches, including manual physiotherapy, osteopathy, patient education, medication, and splint therapy.
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Frequently asked questions
The lateral pterygoid muscle is the muscle that depresses the mandible.
The lateral pterygoid muscle is also known as the external pterygoid muscle.
The lateral pterygoid muscle is responsible for the depression of the mandible, allowing for the opening of the jaw. It also assists with protrusion and side-to-side movement of the mandible.
An injury to the lateral pterygoid muscle can cause problems with chewing and swallowing, leading to symptoms such as jaw pain, joint noise, difficulty eating, and speaking.
Treatments for issues with the lateral pterygoid muscle include physiotherapy, behavioural therapy, medication, surgery, alternative medicine, and in some cases, the injection of botulinum toxin (Botox) directly into the muscle.
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