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The muscles of mastication are a group of muscles that enable chewing and grinding food by moving the jaw (mandible) at the temporomandibular joint. The four main muscles of mastication are the temporalis, masseter, medial pterygoid, and lateral pterygoid muscles. These muscles attach to the mandible and produce movements such as elevation, depression, protrusion, retraction, and side-to-side motion. The masseter muscle, for example, is a strong, quadrangular muscle with two layers that arises from the zygomatic bone and arch, attaching to the ramus of the mandible.
| Characteristics | Values |
|---|---|
| Number of muscles | 4 primary muscles and other secondary or accessory muscles |
| Primary muscles | Temporalis, Masseter, Medial Pterygoid, Lateral Pterygoid |
| Functions | Chewing, grinding food, approximating teeth, moving the jaw (mandible) |
| Movements | Elevation, depression, protrusion, retraction, side-to-side movement |
| Origin | The first pharyngeal arch |
| Innervation | Mandibular branch of the trigeminal nerve (CN V3) |
| Arterial supply | Branches of the maxillary artery |
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What You'll Learn
The four main muscles of mastication
Mastication, or the process of chewing food, involves the movement of the jaw (mandible) at the temporomandibular joint (TMJ). This movement is facilitated by the four main muscles of mastication, which originate from the surface of the skull and attach onto the rami of the mandible. These four muscles are 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 has a fan-shaped structure, with its muscle fibres converging anteriorly to form a tendon that connects to the coronoid process and the anterior border of the ramus of the mandible. The temporalis muscle functions primarily as an elevator of the mandible, with its anterior vertical fibres contributing to closing the mouth against the force of gravity. Additionally, the contraction of its posterior fibres 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 is composed of two layers: a larger, superficial layer that arises from the maxillary process of the zygomatic bone and the anterior portion of the zygomatic arch, and a deep layer that originates from the medial surface and inferior margin of the zygomatic arch. These muscle fibres converge to insert onto the upper part of the ramus of the mandible and the coronoid process. The masseter muscle is the most powerful muscle of mastication, responsible for elevating the mandible and assisting in protrusion, which moves the mandible forward.
The medial pterygoid muscle is a quadrangular muscle situated in the infratemporal fossa. It has two heads: a larger deep head that arises from the medial surface of the lateral pterygoid plate of the sphenoid bone and the adjacent pyramidal process of the palatine bone, and a smaller superficial head that originates from the tuberosity of the maxilla. Both heads attach to the ramus of the mandible near the angle of the mandible. The medial pterygoid muscle contributes to the elevation of the mandible.
The lateral pterygoid muscle has a triangular shape with two heads: the superior and inferior heads. The superior head originates from the greater wing of the sphenoid, while the inferior head arises from the lateral pterygoid plate of the sphenoid. The lateral pterygoid muscle fibres converge to form a tendon that inserts onto the pterygoid fovea of the neck of the condylar process of the mandible. This muscle is the sole muscle responsible for causing depression of the mandible, with the assistance of gravity. It also aids in protrusion and side-to-side movement of the mandible.
In summary, the four main muscles of mastication—the temporalis, masseter, medial pterygoid, and lateral pterygoid muscles—work together to produce the cardinal mandibular movements of mastication, including elevation, depression, protrusion, retraction, and side-to-side motion. These muscles enable essential functions such as chewing and grinding food.
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The role of the trigeminal nerve
The trigeminal nerve is a three-part nerve in the human head that sends signals from the brain to the face and vice versa. There are two trigeminal nerves, one on each side of the head, and they are responsible for sensation in the face and motor functions such as biting and chewing. The trigeminal nerve is the fifth cranial nerve, or CN V, and it is the most complex of the cranial nerves. The nerve is named trigeminal, from the Latin "tri" meaning three, and "geminus" meaning twin, because each of the two nerves has three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3).
The ophthalmic and maxillary nerves are purely sensory, while the mandibular nerve supplies motor as well as sensory functions. The mandibular branch of the trigeminal nerve innervates the muscles of mastication. These muscles 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, the temporalis, and the medial and lateral pterygoid muscles.
The trigeminal nerve carries general somatic afferent fibres (GSA), which innervate the skin of the face via the ophthalmic (V1), maxillary (V2), and mandibular (V3) divisions. The nerve also carries special visceral efferent (SVE) axons, which innervate the muscles of mastication via the mandibular (V3) division. The motor component of the mandibular division (V3) of the trigeminal nerve controls the movement of eight muscles, including the four muscles of mastication. The trigeminal nerve also plays a role in swallowing by supporting the digastric and mylohyoid muscles.
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Accessory muscles
Mastication, or chewing, involves the movement of the mandible at the temporomandibular joints (TMJs). The muscles of mastication can be divided into primary and secondary (accessory) muscles. The primary muscles of mastication include the masseter, temporalis, lateral pterygoid, and medial pterygoid muscles. These muscles originate from the bones of the skull and insert onto the mandible, allowing for movements such as elevation, depression, protrusion, retraction, and side-to-side movement of the jaw.
The accessory muscles of mastication include the digastric, mylohyoid, geniohyoid, and buccinator muscles. These muscles work alongside the primary muscles to facilitate the complex movements of the mandible during mastication. The digastric muscle, for example, assists in depressing the mandible, while the buccinator muscle, a facial expression muscle, helps in mastication by keeping food pushed back within the oral cavity.
The digastric muscle is part of the suprahyoid muscle group, which also includes the mylohyoid and geniohyoid muscles. These muscles work together to depress the mandible against resistance when the infrahyoid muscles fix or depress the hyoid bone. This coordinated action between the suprahyoid and infrahyoid muscles contributes to the overall stability and movement of the mandible during the chewing process.
The accessory muscles of mastication are innervated by the mandibular branch of the trigeminal nerve, specifically the motor fibers known as CN V3. This is in contrast to most other facial muscles, which are innervated by the facial nerve or CN VII. The trigeminal nerve has both sensory and motor functions, allowing for the complex control and coordination of the accessory muscles during mastication.
In summary, the accessory muscles of mastication play a crucial role in supporting the primary muscles during the chewing process. They enable a range of jaw movements, including depression, protrusion, and retraction, and their coordinated action with other muscle groups ensures the smooth and efficient functioning of the mandible during mastication.
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Bruxism and its effects
Mastication, or chewing, is facilitated by the temporalis, masseter, and medial and
Bruxism can exert extremely powerful forces on the teeth, leading to tooth wear, destruction of tooth enamel, and increased tooth sensitivity. The condition can also cause pain in the temporomandibular joint and masticatory muscles, resulting in tension-type headaches. The forces generated during bruxism can reach up to 250 pounds, even while sleeping.
The causes of bruxism are not always clear, but it is often associated with stress, anxiety, and certain personality traits. It is more common in individuals who are aggressive, hurried, or highly competitive. Additionally, bruxism may be a side effect of certain medications, particularly antidepressants, and substances such as tobacco, alcohol, caffeine, and illicit drugs. Bruxism is also linked to various neurological and sleep disorders, including obstructive sleep apnea and Rett syndrome.
The treatment options for bruxism include behavioural changes, such as learning proper tongue, teeth, and lip positioning, and the use of mouth guards to protect the teeth from damage. Biofeedback tools can be used to monitor and reduce muscle activity in the mouth and jaw, especially for daytime bruxism. In severe cases, botulinum toxin injections may be offered if other treatments are ineffective.
In summary, bruxism is a condition involving involuntary teeth clenching or grinding that can lead to various oral health issues. While the causes are multifaceted and not fully understood, stress and certain personality traits are often contributing factors. Treatment options are available to manage the condition and prevent further dental damage.
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Jaw dysfunction
The muscles of mastication are a group of muscles responsible for the chewing movement of the mandible at the temporomandibular joint (TMJ). These include the temporalis, masseter, medial pterygoid, and lateral pterygoid muscles. Jaw dysfunction, or temporomandibular disorder (TMD), refers to a group of conditions causing pain and dysfunction in the jaw joint and muscles that control jaw movement. TMDs can cause a variety of symptoms, including:
- Jaw stiffness
- Limited movement or locking of the jaw
- Painful clicking, popping, or grinding in the jaw joint when opening or closing the mouth
- Ringing in the ears, hearing loss, or dizziness
- Headaches
- Back pain
- Sleep problems
- Changes in the way the upper and lower teeth fit together
The exact causes of TMDs are often unclear, but they can sometimes be caused by injury to the jaw or TMJ. In some cases, TMDs can become chronic or long-lasting, and they can occur simultaneously with other medical conditions. While there is no standard test for diagnosing TMDs, a doctor or dentist will typically ask about symptoms, take a detailed medical history, and examine the head, neck, face, and jaw for tenderness, clicking or popping sounds, and difficulty with movement.
It is important to note that some people may experience clicking or popping sounds in their TMJs without any associated pain, which is considered normal and does not require treatment. However, if you are experiencing any pain or other symptoms of jaw dysfunction, it is advisable to seek medical advice.
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Frequently asked questions
The muscles of mastication are the temporalis, masseter, medial pterygoid, and lateral pterygoid muscles. They are responsible for the chewing movement of the mandible at the temporomandibular joint (TMJ).
The muscles of mastication enable functions such as chewing, grinding, and moving the jaw. They also help bring the teeth together or close them.
The temporalis muscle is a large, flat, fan-shaped muscle that lies within the temporal fossa of the skull. It arises from the temporal fossa and inserts on the apex and medial surface of the coronoid process and the anterior border of the ramus of the mandible.
