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The masticatory muscles are a group of muscles that enable functions such as chewing and grinding. These muscles are involved in the movement of the lower jaw, including protrusion, retraction, elevation, depression, and rotation. The four main masticatory muscles are the temporalis, masseter, medial pterygoid, and lateral pterygoid muscles. Masticatory muscle disorders include myofascial pain, myositis, neoplasms, and myospasm. Bruxism, characterised by teeth clenching or grinding, can cause extreme forces on the masticatory muscles, leading to pain and tension headaches.
| Characteristics | Values |
|---|---|
| Definition | Muscles involved in the chewing process |
| Types | Temporalis, masseter, medial pterygoid, lateral pterygoid, buccinator, suprahyoid, infrahyoid |
| Location | The temporalis muscle is in the temporal fossa; the masseter muscle is in the cheek area; the medial and lateral pterygoids are in the infratemporal fossa |
| Function | Elevation, depression, protrusion, retraction, rotation, and side-to-side movement of the mandible |
| Innervation | Trigeminal nerve, mandibular branch (V3) |
| Blood Supply | Branches of the maxillary artery |
| Disorders | Myofascial pain, myositis, neoplasms, myospasm, myofibrotic contracture, TMJ dysfunction, bruxism |
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What You'll Learn
The four main masticatory muscles
The temporalis muscle is a large, flat muscle that lies within the temporal fossa of the skull. Its main function is to elevate the mandible, with its anterior vertical fibres opposing gravity to keep the mouth closed. The contraction of its posterior fibres also results in the retraction of the mandible, pulling the jaw backwards.
The masseter muscle is a strong, quadrangular muscle that covers the lateral aspect of the ramus of the mandible. It has two parts: deep and superficial. Its primary function is to elevate the mandible, with a minor contribution to the protrusion of the mandible.
The medial pterygoid muscle is quadrangular and situated in the infratemporal fossa. It has two heads with distinct origins: the larger deep head and the smaller superficial head. This muscle is involved in the protrusion of the mandible.
The lateral pterygoid muscle is triangular and also located in the infratemporal fossa. Similar to the medial pterygoid, it has two heads: a smaller superior head and a larger inferior head. The lateral pterygoid is the major protractor of the mandible, enabling the forward movement of the jaw.
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Masticatory muscle disorders
The masticatory muscles are a group of muscles that include the temporalis, masseter, lateral pterygoid, and medial pterygoid. These muscles are responsible for the movement of the jaw, or mandible, and enable essential functions such as chewing and grinding food. The temporalis muscle, located in the temporal fossa, is a large, flat muscle that contributes to elevating the mandible. The masseter muscle, situated in the cheek area, also plays a role in elevating the mandible and contributes to protrusion. The lateral and medial pterygoid muscles lie in the infratemporal fossa and assist in mandibular movements.
Myalgia, a dull persistent ache affecting the jaw and temple muscles, can radiate to other areas such as the head, neck, ear, and teeth. It may also be accompanied by symptoms like restricted jaw opening, fatigue, and stiffness. Localized myalgia specifically affects the masseter and temporalis muscles bilaterally. Diagnosing masticatory muscle disorders involves a careful medical and habit history, along with palpation and imaging techniques such as ultrasonography, CT scans, and MRI. Treatment options include physical therapy, muscle stretches, massages, and education on reducing muscle overuse.
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The role of the temporalis muscle
The temporalis muscle is a masticatory muscle that facilitates the movement of the mandible. It is a large, thin, fan-shaped muscle that lies within the temporal fossa of the skull. The muscle fibres converge anteriorly to form a tendon, which inserts onto the coronoid process of the mandible. The temporalis muscle is innervated by the deep temporal branches of the mandibular nerve and is vascularized by the deep temporal branches of the maxillary artery and middle temporal branches of the superficial temporal artery.
The main function of the temporalis muscle is to produce movements of the mandible at the temporomandibular joint, thus facilitating the act of mastication. The anterior portion of the muscle moves the mandible upwards (elevation), while the posterior portion pulls the mandible backward (retrusion). The middle portion, which contains oblique fibres, is used for both elevation and retraction of the mandible. Additionally, the unilateral contraction of the temporalis muscle plays a crucial role in the side-to-side movements of the jaw during chewing.
The temporalis muscle is a powerful muscle and is considered the primary retractor of the mandible. It is involved in jaw pain and headaches, often resulting from bruxism (teeth grinding) or clenching of the jaw. The muscle can also be used in reconstructive surgery of the mouth and face, particularly in the rehabilitation of the paralyzed face and reconstruction of the skull base.
In summary, the temporalis muscle is a key masticatory muscle that enables essential jaw movements for chewing and grinding food. Its functions include elevation, retrusion, and side-to-side movements of the mandible. The muscle is also implicated in certain medical conditions and has applications in surgical procedures.
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The masseter muscle
The masseter is a paired muscle, with one part originating from the maxillary process of the zygomatic bone and the other part originating from the zygomatic arch. The muscle then extends down to the mandibular angle, inserting along the angle and lateral surface of the mandibular ramus. The deep portion of the masseter muscle originates from the entire surface of the zygomatic arch, with its fibres running inferiorly and inserting along the mandibular ramus superior to the masseter muscle's superior portion. The masseter muscle is covered by a thin but very strong masseteric fascia. The duct of the parotid gland passes across the surface of the muscle, opening onto the inner side of the cheek. The parotid gland surrounds the entire posterior and most of the superficial aspect of the muscle.
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The pterygoid muscles
The lateral pterygoid 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 muscle is innervated by the nerve to the lateral pterygoid muscle, which is a branch of the mandibular division of the trigeminal nerve (CN V3). It receives blood supply from the pterygoid branches of the maxillary artery and the ascending palatine branch of the facial artery. The function of the lateral pterygoid muscle is to protrude and depress the mandible when contraction is bilateral. In unilateral contraction, the lateral pterygoid muscle moves the mandible medially and rotates it.
The medial pterygoid muscle is a thick quadrilateral muscle that arises by two heads, a superficial and a deep head. The smaller superficial head originates from the maxillary tuberosity and pyramidal process of the palatine bone. The larger deep head originates from the medial surface of the lateral plate of the pterygoid process and the pyramidal process of the palatine bone. The medial pterygoid muscle is supplied by the medial pterygoid nerve, a branch of the mandibular nerve, itself a branch of the trigeminal nerve (V). This also supplies the tensor tympani muscle and the tensor veli palatini muscle. The medial pterygoid nerve is a main trunk from the mandibular nerve, before the division of the trigeminal nerve. The medial pterygoid muscle has functions including elevating the mandible (closing the mouth), protruding the mandible, mastication (especially when the maxillary teeth and the mandibular teeth are close together), and excursing the mandible (contralateral excursion occurs with unilateral contraction).
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Frequently asked questions
Masticatory muscles are the muscles involved in the chewing process, including elevation, depression, protrusion, retraction, and lateral movement of the mandible.
The main masticatory muscles are the temporalis, masseter, medial pterygoid, and lateral pterygoid muscles.
The temporalis muscle is the largest masticatory muscle and works with the masseter muscle to produce biting force. It is involved in elevating the mandible and closing the mouth.
The masseter muscle is the most powerful masticatory muscle and is involved in elevating the mandible and closing the mouth.
Masticatory muscle disorders include myofascial pain, myositis, neoplasms, myofibrotic contracture, and masticatory myospasm.
