Victor Forge
The muscles of mastication are a group of muscles that enable the movement of the jaw. They are responsible for chewing food and enhancing the eating process. There are four main muscles of mastication: the masseter, temporalis, medial pterygoid, and lateral pterygoid. These muscles work together to produce mandibular movements such as elevation, depression, protrusion, retraction, and side-to-side motion. The masseter muscle, being the most powerful muscle of mastication, plays a crucial role in elevating the jaw. The temporalis muscle contributes to jaw retraction and grinding movements, while the lateral pterygoid is responsible for jaw depression and protrusion. The medial pterygoid assists in protrusion and elevation, working in coordination with the lateral pterygoid for side-to-side movements during chewing.
| Characteristics | Values |
|---|---|
| Number of muscles of mastication | 4 |
| Names of muscles of mastication | Masseter, temporalis, medial pterygoid, lateral pterygoid |
| Origin of muscles of mastication | Surface of the skull |
| Attachment of muscles of mastication | Rami of the mandible |
| Innervation of muscles of mastication | Motor branches of the mandibular division of the trigeminal nerve (CNV3) |
| Main arterial supply to muscles of mastication | Branches of the maxillary artery |
| Main functions of muscles of mastication | Elevation, depression, protrusion, retraction, side-to-side movement |
| Number of heads of the lateral pterygoid muscle | 2 (superior and inferior) |
| Origin of the superior head of the lateral pterygoid muscle | Inferior temporal surface of the greater wing of the sphenoid bone |
| Origin of the inferior head of the lateral pterygoid muscle | Lateral aspect of the lateral pterygoid plate of the sphenoid bone |
| Number of heads of the medial pterygoid muscle | 2 (superficial and deep) |
| Origin of the superficial head of the medial pterygoid muscle | Maxillary tuberosity of the inferior maxilla |
| Origin of the deep head of the medial pterygoid muscle | Medial surface of the lateral pterygoid plate of the sphenoid bone |
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What You'll Learn
The role of the temporalis muscle
The temporalis muscle is a powerful muscle of the temporomandibular joint. It is a fan-shaped convergent muscle on each side of the head that fills the temporal fossa, superior to the zygomatic arch. The muscle is covered by the temporal fascia, also known as the temporal aponeurosis. The temporalis muscle is the third most commonly involved of the masticatory muscles. It is also the primary retractor of the mandible.
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 (closing the mouth). The posterior portion has fibres that run horizontally, and contraction of this portion results in retrusion of the mandible. The middle portion, with fibres running in an oblique direction towards the inferior and anterior, is used for both elevation and retraction of the mandible. The unilateral contraction of the temporalis muscle plays an important role in the side-to-side movements of the jaw, contributing to grinding movements by moving the mandible from side to side.
The temporalis muscle is involved in jaw pain and headaches. Bruxism, or the habitual grinding of teeth, typically while sleeping, and clenching of the jaw while stressed, can lead to overwork of the temporalis muscle and result in pain. A myotendinous rupture of the temporalis muscle can occur during a seizure due to extreme clenching of the jaw. During a seizure, the contralateral temporalis muscle can enter spastic paralysis, and this clenching can lead to a rupture at the myotendinous insertion.
The temporalis muscle is also used in reconstructive surgery of the mouth and face. It has been used in the reconstruction of the paralyzed face and in defects involving the skull base, orbit, midface, and oropharynx. During pterional craniotomy, incisions are often chosen based on the ease of reattaching the temporalis muscle after the bone fragment is replaced.
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The role of the masseter muscle
The masseter muscle is one of the four muscles of mastication, along with the temporalis, medial pterygoid, and lateral pterygoid muscles. 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. 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 superficial layer and a deep layer. The superficial layer is larger and arises from the maxillary process of the zygomatic bone, while the deep layer originates from the inferior surface of the zygomatic arch.
The masseter muscle is involved in the elevation and protrusion of the mandible, as well as providing support to the articular capsule of the temporomandibular joint. The contraction of the entire muscle results in the elevation of the mandible, raising the lower jaw during the closing of the jaws. The deep part of the masseter muscle allows the mandible to elevate, enabling the mouth to close. On the other hand, the superficial part of the masseter moves the mandible forward, bringing the lower front teeth in front of the upper front teeth.
The masseter muscle is a large muscle located on both sides of the face, extending from the cheekbone down to the angle of the mandible. It is one of the few muscles that help with mandibular movements and is unique to mammals. The masseter muscle is also involved in mastication, the process of chewing food. Singers often experience tension in this muscle, which can be treated with transdermal massages or stretches as part of vocal warm-up routines.
The masseter muscle can become enlarged in individuals who habitually clench or grind their teeth, a condition known as bruxism. This enlargement, called masseteric hypertrophy, is typically asymptomatic and soft, but it can lead to asymmetry in the face due to unequal enlargement of the muscles. The masseter muscle is susceptible to infections, such as Clostridium tetani, which can cause strong and persistent spasms known as trismus or "lockjaw," interfering with normal feeding.
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The role of the medial pterygoid muscle
The medial pterygoid muscle is a thick quadrilateral muscle that connects the mandible with the maxilla, sphenoid, and palatine bones. It is one of the four muscles of mastication, along with the lateral pterygoid, masseter, and temporalis muscles. These muscles work together to produce mandibular movements for chewing food.
The medial pterygoid muscle consists of two heads: a superficial head and a deep head. The deep head is larger and arises from the medial surface of the lateral pterygoid plate of the sphenoid bone. The superficial head originates from the maxillary tuberosity of the inferior maxilla. The muscle fibres converge inferiorly, forming a tendon that inserts on the medial ramus of the mandible.
The medial pterygoid muscle is innervated by the medial pterygoid branch of the mandibular nerve, a branch of the trigeminal nerve. It receives its blood supply primarily from the pterygoid and buccal branches of the maxillary artery. The unilateral contraction of the medial pterygoid muscle causes a slight medial rotation of the mandible. When this occurs simultaneously with the contraction of the ipsilateral lateral pterygoid muscle, the same-sided part of the mandible swings anteriorly and medially.
Bilateral contraction of the medial pterygoid muscle, on the other hand, elevates and protrudes the mandible. This action, in synergy with other masticatory muscles, facilitates chewing and the grinding of food. The medial pterygoid muscle is crucial for producing movements of the mandible at the temporomandibular joint, enabling essential functions such as chewing and speaking.
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The role of the lateral pterygoid muscle
The lateral pterygoid muscle is a key muscle involved in mastication (chewing). It is one of four masticatory muscles, along with the medial pterygoid, temporalis, and masseter muscles. These muscles act on the temporomandibular joint (TMJ) to enable chewing and biting. The lateral pterygoid muscle is located in the infratemporal fossa of the skull, with its belly separated into two heads: superior (upper) and inferior (lower). The superior head is smaller and arises from the infratemporal crest of the greater wing of the sphenoid bone, while the larger inferior head originates from the lateral surface of the lateral pterygoid plate.
The fibres from both heads merge and insert onto a shallow depression called the pterygoid fovea on the neck of the mandible. Additionally, some fibres insert onto the articular disc and capsule of the temporomandibular joint (TMJ). This insertion onto the TMJ enables the lateral pterygoid muscle to produce gliding motions of the disc and mandibular condyle. The inferior head acts on the inferior compartment of the TMJ, facilitating a hinge-like rotation between the mandibular condyle and the articular disc.
The function of the lateral pterygoid muscle depends on the type of contraction. During bilateral contraction, the muscle protrudes and depresses the mandible, contributing to jaw opening. Conversely, unilateral contraction of the lateral pterygoid muscle, in conjunction with the ipsilateral medial pterygoid muscle, moves the mandible to the opposite side, enabling side-to-side movements essential for chewing. Thus, the lateral pterygoid muscle plays a crucial role in mandibular movements during mastication, allowing for protrusion, depression, and side-to-side rotation of the jaw.
The lateral pterygoid muscle is innervated by the nerve to the lateral pterygoid muscle, a branch of the mandibular division of the trigeminal nerve (CN V3). It receives its blood supply from the pterygoid branches of the maxillary artery and the ascending palatine branch of the facial artery. The understanding of the anatomy and functions of the lateral pterygoid muscle is important for comprehending jaw movements and disorders associated with the temporomandibular joint.
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How these muscles work together
The muscles that move the jaw are the masseter, temporalis, and the internal and external pterygoids (medial and lateral pterygoids). These muscles work together to produce mandibular movements for chewing food.
The masseter muscle is the most powerful muscle of mastication. It is quadrangular in shape and split into two regions, deep and superficial. It covers the other muscles of mastication. The masseter elevates the jaw.
The temporalis muscle is a broad muscle that fans out to cover much of the temporal bone on the side of the skull. It has a wide, fan-shaped origin on the side of the skull and condenses into a tendon that attaches to the jaw. The temporalis muscle elevates and retracts the jaw. The posterior fibres of the temporalis muscle function to retract the mandible and also contribute to side-to-side grinding movements.
The lateral pterygoid muscle has a triangular shape with two heads, superior and inferior. It is the major protractor (opener) of the jaw. The lateral pterygoid muscle functions as the sole muscle of mastication to cause depression of the mandible. It also assists with protrusion and side-to-side movement of the mandible. Bilateral contraction of the lateral pterygoid muscles protrudes and depresses the mandible. A unilateral contraction on a particular side, in conjunction with the ipsilateral medial pterygoid muscle, moves the mandible to the opposite side.
The medial pterygoid muscle is thick and rectangular with a superficial head and a deep head. The deep head is larger than the superficial head. The medial pterygoid muscle is involved in protrusion of the mandible and assists in the production of lateral movement.
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Frequently asked questions
The four main muscles that move the jaw (also known as the mandible) are the masseter, temporalis, medial pterygoid, and lateral pterygoid.
The masseter muscle is the most powerful muscle of mastication. It is responsible for elevating the jaw and is also involved in everting, or turning outwards, the lower edges of the mandible.
The temporalis muscle is involved in elevating and retracting the mandible. It also contributes to side-to-side grinding movements.
The medial pterygoid muscle assists in the elevation of the mandible and is involved in protrusion and lateral movements during chewing.
The lateral pterygoid muscle is the primary muscle responsible for depressing (opening) the jaw. It also assists in protrusion and lateral movements of the mandible.
