Logan Steele
The human body is a fascinating structure, with many intricacies and complexities that allow us to perform various functions. One such function is the ability to open our mouths, which is facilitated by a group of muscles called the muscles of mastication. These muscles are primarily responsible for the chewing movement of the mandible, assisting in grinding food and enhancing the process of eating. While several muscles aid in jaw movement, only a few are dedicated solely to mastication, and understanding their mechanics provides insight into our daily activities, such as chewing and talking.
| Characteristics | Values |
|---|---|
| Number of muscles whose sole purpose is to open the mouth | 1 |
| Name of the muscle | Lateral pterygoid |
| Other muscles that help in the process | Muscles of the tongue and cheeks |
| Other functions of the muscle | Opening the jaw, moving it from side to side, and closing it |
| Origin of the muscle fibres | Inferior zygomatic arch and the anterior two-thirds of the zygomatic arch |
| Insertion of the muscle fibres | Outer surface of the mandibular ramus and the coronoid process of the mandible |
| Innervation | Mandibular division of the trigeminal nerve |
| Blood supply | Masseteric artery, a branch of the maxillary artery |
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What You'll Learn
The lateral pterygoid muscle opens the mouth
The mouth is opened and closed by a group of muscles known as the muscles of mastication. These muscles are responsible for the chewing movement of the mandible at the temporomandibular (TMJ) joint, enhancing the process of eating and assisting in grinding food. There are four main muscles of mastication: the masseter, temporalis, and medial and lateral pterygoid muscles. While the former three are dedicated to closing the jaw, the lateral pterygoid muscle is the only one responsible for opening the jaw.
The lateral pterygoid muscle sits just outside of the medial pterygoid and, in addition to opening the jaw, assists in side-to-side motion. The masseter and medial pterygoid muscles also help the jaw move from side to side, while the temporalis muscle, which sits along the side of the skull, is responsible for retracting the jaw. The vertical fibres of the temporalis muscle help to close the jaw, running top to bottom, while the horizontal fibres are responsible for retracting the jaw, running from front to back.
All of these muscles are innervated by the mandibular branch of the trigeminal nerve, which is both sensory and motor. They are also supplied by branches of the maxillary artery. The masseter muscle, for example, is supplied by the masseteric artery, which emerges from the maxillary artery. The masseter muscle runs from the side of the skull down to the bottom of the jawbone and can be felt tensing when one bites down. Its main function is to help close the jaw.
The muscles of mastication are not the only muscles that aid in the opening and closing of the jaw. There are also secondary muscles that help with the process, such as those of the tongue and the cheeks.
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The masseter, temporalis, and medial pterygoid muscles aid mastication
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 and assist in grinding food. The masseter, temporalis, and medial pterygoid muscles are among the primary muscles of mastication.
The masseter muscle is a strong, quadrangular muscle that covers the lateral aspect of the ramus of the mandible. It is composed of two or three layers that differ slightly in their attachments. The larger, superficial layer arises from the maxillary process of the zygomatic bone and the anterior two-thirds of the zygomatic arch. The deep layer of the masseter muscle arises from the medial surface and inferior margin of the zygomatic arch. The major function of the masseter muscle is to elevate the mandible and approximate the teeth.
The temporalis muscle originates from the temporal fossa, a shallow depression on the lateral aspect of the skull. It is covered by tough fascia, which can be harvested surgically and used to repair a perforated tympanic membrane. The muscle fibres converge inferiorly, forming a tendon that exits the temporal fossa and inserts on the coronoid process of the mandible. The temporalis muscle is responsible for the elevation and retraction of the mandible.
The medial pterygoid muscle is also quadrangular and is situated in the infratemporal fossa. It is composed of two heads, the deep head and the superficial head, which have two sets of origins. The larger deep head arises from the medial surface of the lateral pterygoid plate of the sphenoid bone, while the smaller superficial head originates from the tuberosity of the maxilla. The medial pterygoid muscle works with the lateral pterygoid muscle to enable side-to-side movement of the mandible.
These three muscles, along with the lateral pterygoid muscle, are innervated by the motor fibres of the mandibular branch of the trigeminal nerve (CN V3). The main arterial supply for these muscles is derived from branches of the maxillary artery. While these muscles are the primary participants in mastication, other muscles, such as those of the tongue and cheeks, also assist in the process.
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The trigeminal nerve controls the muscles that open the mouth
The trigeminal nerve is the fifth cranial nerve and the largest of the cranial nerves. It is a three-part nerve 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 start in the brain, extending throughout the face.
The trigeminal nerve provides sensory and motor information for different parts of the head and face. The sensory function of the trigeminal nerve is to provide tactile, proprioceptive, and nociceptive afference to the face and mouth. Its motor function activates the muscles of mastication, which are a group of muscles responsible for the chewing movement of the mandible at the temporomandibular joint. These muscles enhance the process of eating and assist in grinding food. The trigeminal nerve carries general somatic afferent fibres (GSA), which innervate the skin of the face via ophthalmic (V1), maxillary (V2), and mandibular (V3) divisions.
The mandibular nerve (V3) is the trigeminal nerve's largest branch and the only branch with both sensory and motor components. The nerve carries sensory information from the lower lip, lower teeth and gums, chin, and jaw. The mandibular nerve also plays a role in swallowing by supporting the digastric muscle and mylohyoid muscle. 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 masseter, the temporal muscle, and the medial and lateral pterygoids.
Trigeminal nerve damage can result in facial numbness or tingling, facial pain, jaw muscle spasms or weakness, and difficulty chewing, speaking, or swallowing.
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Myofibrotic contracture can limit mouth opening
The mouth is opened by the muscles of mastication, which are a group of muscles responsible for the chewing movement of the mandible at the temporomandibular (TMJ) joint. These muscles also assist in grinding food and approximating the teeth.
Myofibrotic contracture is just one example of a condition that can restrict mouth opening. Other conditions that can limit mouth opening include myostatic contracture, which may be secondary to another disorder, and microstomia, which can be caused by scleroderma, diffuse systemic sclerosis, oro-facial trauma, or surgical resections. Oral splints and other intraoral stretching techniques are often used to manage microstomia and improve mouth opening.
In some cases, limited mouth opening may be a result of surgical resections or trauma to the oral cavity structures, leading to fibrosis, scarring, and altered mandibular motion. Radiotherapy can also cause perioral tissue fibrosis, impacting the range of motion of the mandible. Patients with limited mouth opening due to these causes can be managed through gentle handling of circum-oral soft tissues and the use of smaller instruments.
Additionally, certain disorders can contribute to restricted mouth opening. For example, masticatory myalgia is characterized by a persistent ache in the jaw and temple muscles, with symptoms including restricted opening, fatigue, and stiffness. Masticatory myospasm, or muscle cramp, can also lead to lockjaw and severely limited range of motion of the mandible.
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Myositis can cause jaw dysfunction and limit mouth movement
The muscles of mastication are a group of muscles that control the movement of the mandible at the temporomandibular (TMJ) joint, enabling processes such as eating, grinding food, and approximating the teeth. The mandible is the only bone that moves during mastication and other activities, such as talking. The TMJ joints are the two joints that connect the lower jaw to the skull, consisting of the mandible (lower jaw) and the temporal bone (side and base of the skull).
TMJ dysfunction, or temporomandibular disorder (TMD), is a condition that affects these jaw joints and the surrounding muscles and ligaments. Symptoms include jaw pain, headaches, and difficulty opening and closing the mouth. Myositis is an inflammatory condition of the muscles that can be caused by acute trauma or infection, leading to swelling, redness, and increased temperature in the affected area. Myositis is one such condition that can cause jaw dysfunction and limit mouth movement.
Myositis is characterised by swelling and inflammation of the muscles, resulting in restricted movement. In the case of jaw dysfunction, this can manifest as difficulty opening the mouth widely, limited range of motion when chewing, and even lockjaw. The inflammation and swelling associated with myositis can affect the complex system of muscles, ligaments, disks, and bones that work together to enable smooth jaw movements.
While the exact cause of myositis in the jaw muscles may vary, it is often associated with acute trauma or infection. For example, a sudden injury to the jaw or face can lead to myositis in the affected muscles, causing swelling and pain that restricts mouth movement. Similarly, an infection in the jaw area can lead to inflammation and swelling of the muscles, impacting their ability to function properly and limiting the range of motion of the jaw.
It is important to note that jaw dysfunction and limited mouth movement can also result from other conditions, such as bruxism (involuntary teeth grinding or clenching), arthritis, or trauma to the jaw, head, or neck. A healthcare provider can diagnose jaw dysfunction through a dental check-up or physical examination, and imaging tests may be conducted to get a closer look at the jaw joints and surrounding structures.
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Frequently asked questions
The lateral pterygoid muscle is responsible for opening the mouth.
The masseter, temporalis, and medial pterygoid muscles, along with the muscles of the tongue and cheeks, assist in jaw movement.
The masseter muscle helps elevate the mandible and close the jaw.
The temporalis muscle aids in closing and retracting the jaw.
There are four primary muscles involved in mastication: the masseter, temporalis, and medial and lateral pterygoid muscles.
