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The mandible is the only movable bone in the skull, and its movement is facilitated by the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles. These muscles are responsible for the chewing motion of the mandible at the temporomandibular joint (TMJ). The lateral pterygoid muscle is the primary muscle responsible for opening the mandible, allowing for jaw movement during activities such as talking and chewing.
| Characteristics | Values |
|---|---|
| Muscles that open the mandible | Lateral pterygoid muscle, Digastric, Geniohyoid, Mylohyoid, Omohyoid, Sternohyoid, Sternothyroid, Stylohyoid, Thyrohyoid |
| Muscles that close the mandible | Masseter, Temporalis, Medial pterygoid |
| Main function | Mastication (chewing food) |
| Other functions | Elevation, depression, protrusion, retraction, side-to-side movement, grinding food, bringing teeth together |
| Blood supply | External carotid artery, maxillary artery and its branches |
| Innervation | Motor branches of the mandibular division of the trigeminal nerve (CNV3) |
| Main arterial supply | Branches of the maxillary artery |
| Masticatory muscle disorders | Myofascial pain, myositis, neoplasms, myospasm (muscle cramp) |
| Masticatory system issues | Osteoarthrosis, osteoarthritis, degenerative joint disease |
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What You'll Learn
The lateral pterygoid muscle is the primary opener of the mandible
The lateral pterygoid muscle is a craniomandibular muscle that is active during mandibular movements, including protrusion, abduction, and mediotrusion. It is the only muscle out of the four muscles of mastication (medial pterygoid, lateral pterygoid, masseter, and temporalis) that participates in depressing the mandible. The lateral pterygoid muscle has two heads or bellies, the inferior belly and the superior belly, which were traditionally believed to have opposing functions. The inferior belly was thought to depress, protrude, and deviate the mandible to the contralateral side, while the superior belly was believed to be active during the elevation of the mandible to close the mouth. However, recent studies suggest that the superior belly may have little role in closing the mouth and may instead be active during mouth opening, similar to the inferior belly.
The lateral pterygoid muscle is supplied by a branch of the anterior division of the mandibular nerve and receives blood supply from the pterygoid branch of the maxillary artery. It is a short, two-headed muscle located in the infratemporal fossa of the skull. The smaller superior head arises from the infratemporal crest of the greater wing of the sphenoid bone, while the larger inferior head arises from the lateral surface of the lateral pterygoid plate. The fibres of both muscle heads merge and insert on the pterygoid fovea on the neck of the mandible.
The lateral pterygoid muscle functions to protrude and depress the mandible when contraction is bilateral. In unilateral contraction, the lateral pterygoid muscle moves the mandible medially. When the lateral pterygoid muscle contracts bilaterally, the mandible moves anteriorly (protrusion). The unilateral contraction of the lateral pterygoid muscle with the ipsilateral medial pterygoid muscle results in lateral mandibular movement to the contralateral side, which is observable during functional and parafunctional lateral excursive movements, such as chewing, masticating, and clenching.
The primary function of the pterygoid muscles, including the lateral pterygoid, is to produce movements of the mandible at the temporomandibular joint. The lateral pterygoid muscle is the major protractor of the mandible due to its horizontally oriented muscle fibres. It is the only muscle among the masticatory muscles with this type of fibre arrangement. The lateral pterygoid muscle is active during speaking, singing, and clenching, and it assists in side-to-side mandibular motion to help with the grinding of food.
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The medial pterygoid assists with mandible opening
The mandible is the only bone that moves during mastication (chewing food) and other activities, such as talking. The medial pterygoid is one of the four muscles of mastication, along with the temporalis, lateral pterygoid, and masseter muscles. The medial pterygoid assists with the movement of the mandible at the temporomandibular joint.
The medial pterygoid is a thick, quadrilateral muscle with two heads: a superficial head and a deep head. The superficial head is smaller and originates from the maxillary tuberosity of the inferior maxilla. The deep head is larger and originates from the medial surface of the lateral pterygoid plate of the sphenoid bone. The medial pterygoid muscle fibres converge inferiorly, forming a tendon that inserts on the medial ramus of the mandible.
The medial pterygoid assists with elevation and protrusion of the mandible. When the medial pterygoid contracts bilaterally, it helps to elevate the mandible and close 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. The medial pterygoid also assists the lateral pterygoid muscle with side-to-side mandibular motion to help with the grinding of food.
The lateral pterygoid muscle is also a crucial muscle for mandibular movements, including protrusion (forward movement of the mandible), abduction (depression of the mandible), and mediotrusion (mandibular condyle movement towards the midline). The lateral pterygoid muscle has two bellies, an inferior belly and a superior belly, and its primary function is to depress the mandible.
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The temporalis muscle closes the mandible
The temporalis muscle is a fan-shaped convergent muscle on each side of the head. It fills the temporal fossa, superior to the zygomatic arch, and covers much of the temporal bone. The temporalis muscle is one of the muscles of mastication, or chewing, and is responsible for the elevation of the mandible, which closes the mouth.
The temporalis muscle can be divided into two functional parts: anterior and posterior. The anterior portion runs vertically, and its contraction results in the elevation of the mandible and the closing of the mouth. The posterior portion has fibres that run horizontally, and the contraction of this portion results in the retrusion of the mandible, or the pulling of the jaw backward.
The middle portion of the temporalis muscle has fibres that run in an oblique direction towards the inferior and anterior. These fibres are used for both the elevation and retraction of the mandible. A unilateral contraction of these fibres provokes a lateral movement of the mandible.
The temporalis muscle is a powerful muscle of the temporomandibular joint. It arises from the temporal fossa and the deep part of the temporal fascia. This is a very broad area of attachment. The muscle forms a tendon that inserts onto the coronoid process of the mandible.
The temporalis muscle is one of four primary muscles of mastication, along with the medial pterygoid, lateral pterygoid, and masseter muscles. These muscles attach to the rami of the mandible and function to move the jaw. The movements performed by these muscles include elevation, depression, protrusion, retraction, and side-to-side movement.
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The masseter muscle closes the mandible
The masseter muscle is one of the four muscles responsible for the action of mastication (chewing). It is a powerful superficial quadrangular muscle that originates from the zygomatic arch and inserts along the angle and lateral surface of the mandibular ramus. The masseter muscle is also involved in the chewing movement of the mandible at the temporomandibular joint (TMJ).
The masseter muscle is a primary muscle of mastication and is one of the strongest muscles in the human body. It is responsible for the elevation of the mandible, causing the mouth to close. Its insertion along the angle and lateral surface of the ramus also allows it to aid in the protrusion of the mandible, enabling anterior motion of the jaw. The masseter muscle has two divisions: superficial and deep. The superficial portion of the masseter muscle originates from a thick aponeurosis on the temporal process of the zygomatic bone and the anterior two-thirds of the inferior border of the zygomatic arch.
The masseter muscle receives its motor innervation from the mandibular division of the trigeminal nerve. The trigeminal nerve carries both sensory and motor fibres. The blood supply to the masseter muscle is primarily provided by the masseteric artery, a branch of the internal maxillary artery. The masseteric artery emerges from the maxillary artery, which itself arises from the external carotid artery behind the neck of the mandible.
The masseter muscle plays a significant role in temporomandibular disorders (TMD), which are conditions affecting the jaw muscles, temporomandibular joints, and associated nerves, resulting in chronic facial pain. Dysfunction of the masseter muscle can lead to pain, chewing difficulties, and swelling around the jaw and face, potentially progressing to TMD. The masseter muscle also contributes to stabilising the TMJ when an individual clenches their teeth.
In summary, the masseter muscle is a crucial muscle involved in mastication and the movement of the mandible. Its contraction results in the elevation of the mandible, leading to the closing of the mouth. Additionally, the masseter muscle has a role in protrusion and retraction of the mandible, allowing for a range of jaw movements.
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The buccinator is a facial expression muscle that assists with mastication
The buccinator is a thin, quadrilateral facial muscle that forms the main component of the cheek. It is the muscle that provides the cheek with structure and tightness. The buccinator muscle is one of the accessory muscles of mastication, which are the muscles that enable chewing. The four main muscles of mastication are the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles. These muscles attach to the rami of the mandible and function to move the jaw.
The buccinator muscle assists with mastication by keeping food pushed back within the oral cavity. It compresses the cheek against the molar teeth, which helps to keep the food bolus central in the mouth. This function is important to prevent food from escaping into the oral vestibule, as well as pushing any food that entered the vestibule back into the oral cavity. The buccinator also prevents the cheeks from inverting between the occlusal surfaces of the teeth and being bitten.
The buccinator muscle has three parts: superior, inferior, and posterior. The superior part arises from the outer surface of the alveolar process of the maxilla, opposite the three maxillary molar teeth. The inferior part arises from the alveolar part of the mandible, opposite the three mandibular molar teeth. The posterior part originates from the anterior margin of the pterygomandibular raphe, a tendinous band behind the third molar. The three parts of the buccinator fill the space between the upper and lower jaws.
The buccinator muscle also has an interesting additional function: expelling air from the inflated vestibule when playing a wind instrument, such as the trumpet. This is why the buccinator muscle is sometimes called the "trumpet muscle".
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Frequently asked questions
The lateral pterygoid muscle is the primary muscle responsible for opening the mandible, also known as the jaw.
The medial pterygoid, masseter, and temporalis muscles are also involved in mandibular movement, primarily responsible for closing the mandible.
The mandible performs several movements, including elevation, depression, protrusion, retraction, and side-to-side movement. These movements are essential for chewing and grinding food.
Several accessory muscles coordinate mandibular movement, including the digastric, geniohyoid, mylohyoid, omohyoid, and stylohyoid muscles. These muscles are indirectly associated with mandibular function and help with jaw opening and closing.
