Maximus Gage
The mandible is the only bone that moves during mastication and other activities such as talking. The muscles of mastication are a group of muscles that are responsible for the chewing movement of the mandible at the temporomandibular joint. These muscles enhance the process of eating and assist in grinding food. There are four main muscles of mastication: the masseter, temporalis, medial pterygoid, and lateral pterygoid. These muscles are responsible for various movements of the mandible, including elevation, depression, protrusion, retraction, and side-to-side movement.
| Characteristics | Values |
|---|---|
| Number of muscles | 4 |
| Names of muscles | Masseter, temporalis, medial pterygoid, lateral pterygoid |
| Functions | Elevation, depression, protrusion, retraction, side-to-side movement |
| Muscle shape | Rectangular, triangular, fan-shaped |
| Muscle origin | Skull, sphenoid bone, zygomatic bone, temporal bone |
| Muscle insertion | Rami of the mandible, coronoid process of the mandible, pterygoid fovea |
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What You'll Learn
The role of the temporalis muscle
The temporalis muscle is a fan-shaped muscle that is one of the four muscles of mastication (the other three being the medial pterygoid, lateral pterygoid, and masseter muscles). It is a powerful muscle of the temporomandibular joint, facilitating the movement of the mandible and thus enabling mastication (chewing). The muscle is divided into two functional parts: the 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 the retrusion of the mandible. The middle portion, which contains oblique fibres, is used for both elevation and retraction of the mandible, and unilateral contraction provokes lateral movement of the mandible.
The temporalis muscle is innervated by the third (mandibular) branch of the trigeminal nerve. Specifically, the muscle is supplied by the deep temporal nerves. The muscle receives its blood supply from the deep temporal arteries, which anastomose with the middle temporal artery. The muscle is covered by the temporal fascia, also known as the temporal aponeurosis, which is commonly used in tympanoplasty, or surgical reconstruction of the eardrum.
The temporalis muscle is also used in reconstructive surgery of the mouth and face. Its proximity to the orbit and anterolateral skull base has allowed its use in skull base reconstruction and orbital cavity obliteration. It is also used in the reconstruction of the paralyzed face and in defects that involve the skull base, orbit, midface, and oropharynx.
The temporalis muscle is likely to be involved in jaw pain and headaches. Bruxism, the habitual grinding of teeth, and clenching of the jaw while stressed can lead to overwork of the temporalis muscle and result in pain.
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The role of the medial pterygoid muscle
The medial pterygoid muscle is a thick, quadrilateral muscle with a superficial head and a deep head. The deep head is larger than the superficial head. The medial pterygoid is one of the four muscles of mastication, which are a group of muscles responsible for the movement of the jaw (mandible). The other three muscles of mastication are the masseter, temporalis, and lateral pterygoid muscles.
The medial pterygoid muscle originates on the pterygoid process, which is a downward-pointing process that extends from the sphenoid bone. The superficial head of the medial pterygoid has its origin from the maxillary tuberosity of the inferior maxilla, while the deep head originates from the medial surface of the lateral pterygoid plate of the sphenoid bone. The muscle fibres converge inferiorly, forming a tendon that inserts on the medial ramus of the mandible, creating an axis for a strong pull of this bone.
The medial pterygoid muscle is innervated by the medial pterygoid branch of the mandibular nerve (CN V3), which is a branch of the trigeminal nerve (CN V). It receives its blood supply primarily from the pterygoid and buccal branches of the maxillary artery. The medial pterygoid muscle is located in the infratemporal fossa, lying deep to the masseter and temporalis muscles and medial to the lateral pterygoid muscle.
The medial pterygoid muscle has several functions, including elevating the mandible (closing the mouth), protruding the mandible, and assisting in mastication (chewing). Unilateral contraction of the medial pterygoid causes a slight medial rotation of the mandible, while bilateral contraction elevates and protrudes it. These movements are crucial for the act of chewing, as they facilitate the grinding of food and the approximation of the teeth.
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The role of the lateral pterygoid muscle
The lateral pterygoid muscle is one of the four muscles of mastication, along with the medial pterygoid, temporalis, and masseter muscles. These muscles are responsible for the movement of the mandible, or jaw, at the temporomandibular joint (TMJ). The lateral pterygoid muscle has a unique role in this process, contributing to specific movements of the mandible.
The lateral pterygoid muscle is a two-headed, fan-shaped muscle located in the infratemporal fossa of the skull. It has a triangular shape, with a smaller superior head and a larger inferior head. The superior head originates from the greater wing of the sphenoid bone, while the inferior head originates from the lateral surface of the lateral pterygoid plate of the sphenoid bone. The fibres from these two heads converge and insert on the pterygoid fovea of the neck of the mandible.
The primary function of the lateral pterygoid muscle is to cause depression of the mandible, or lowering and opening of the jaw. This movement is largely the result of gravity. Additionally, the lateral pterygoid muscle assists in protrusion, or forward movement, of the mandible. When contracting bilaterally, the lateral pterygoid muscle depresses and protrudes the mandible, contributing to the chewing and biting motions.
Unilateral contraction of the lateral pterygoid muscle moves the mandible medially, causing a side-to-side movement. This unilateral action is often performed in conjunction with the medial pterygoid muscle, resulting in the swinging of the mandible to the opposite side. This movement is crucial for the act of chewing, enabling the grinding of food.
The lateral pterygoid muscle is innervated by the lateral pterygoid nerve, a branch of the mandibular nerve (CN V3), which is itself a branch of the trigeminal nerve (CN V). It receives its blood supply from the pterygoid branches of the maxillary artery. The understanding of the anatomy and functions of the lateral pterygoid muscle is important, as it may also be involved in temporomandibular joint dysfunction.
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The role of the masseter muscle
The masseter muscle is a paired, strong, thick, and rectangular muscle with three layers (superficial, deep, and intermediate). It is one of the four muscles of mastication (the other three being the temporalis, medial pterygoid, and lateral pterygoid muscles). The masseter muscle originates from the zygomatic arch and extends down to the mandibular angle, with its fibres passing downward and forward. It is inserted into the upper half of the ramus as high as the coronoid process of the mandible. The nerve supply allows the masseter muscle to perform movements that it is designed to perform, as motor neurons innervate the muscle fibres.
The masseter muscle is involved in mastication, or the process of chewing food. Its functions are elevation and protrusion of the mandible, as well as providing support to the articular capsule of the temporomandibular joint. The superficial part of the masseter functions to move the mandible or lower jaw forward, bringing the lower front teeth in front of the upper front teeth. This allows for the mouth to close. The deep part of the masseter muscle allows the mandible or lower jaw to elevate. The masseter muscle is also believed to be involved in the retraction of the mandible and the stabilization of the mandibular coronoid process.
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 the only muscle of mastication that causes protrusion of the mandible. The superficial head of the masseter originates at the maxillary process of the zygomatic bone (cheekbone) and the inferior (lower) border of the zygomatic arch. The deep head originates at the deep or inferior surface of the zygomatic arch. The entire superficial (lateral) aspect of the muscle is covered with thin but very strong masseteric fascia.
The masseter muscle can become enlarged in patients who habitually clench or grind their teeth, even in those who constantly chew gum. This masseteric hypertrophy is usually asymptomatic and soft, and it is typically bilateral but can be unilateral. Even if the hypertrophy is bilateral, asymmetry of the face may still occur due to unequal enlargement of the muscles. This enlargement may be confused with parotid salivary gland disease, dental infections, and maxillofacial neoplasms.
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How the mandible moves during mastication
The mandible moves during mastication through the action of 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 enhance the process of eating and assist in grinding food, as well as functioning to approximate the teeth. The four main muscles of mastication are the masseter, temporalis, medial pterygoid, and lateral pterygoid. These muscles originate from the surface of the skull and attach onto the rami of the mandible at the TMJ.
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: the superficial layer, which arises from the maxillary process of the zygomatic bone, and the anterior two-thirds of the zygomatic arch. The masseter's main function is to elevate the mandible, with a minor contribution to protrusion of the mandible.
The temporalis muscle is a large, flat muscle that lies within the temporal fossa of the skull. It functions mainly as an elevator of the mandible, with its anterior vertical fibres opposing gravity to keep the mouth closed. The posterior, more horizontal fibres of the temporalis produce a retraction of the mandible, pulling the jaw backwards. The temporalis muscle also contributes to grinding movements by moving the mandible from side to side.
The medial pterygoid muscle is a thick, rectangular muscle with a superficial head and a deep head. The superficial head originates from the maxillary tuberosity of the inferior maxilla, while the deep head 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 lateral pterygoid muscle has a triangular shape with two heads: the superior and inferior. It has horizontally oriented muscle fibres, making it the major protractor of the mandible. The function of the lateral pterygoid depends on the degree of its contraction. Bilateral contraction of the lateral pterygoid muscles results in protrusion and depression of the mandible, while unilateral contraction on one side, along with the ipsilateral medial pterygoid muscle, moves the mandible to the opposite side, enabling side-to-side movements during chewing.
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Frequently asked questions
The mandible is the jawbone.
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 four main muscles involved in mastication are the masseter, temporalis, medial pterygoid, and lateral pterygoid.
The masseter muscle is a strong, quadrangular muscle that covers the lateral aspect of the ramus of the mandible. It assists in raising the mandible and closing the mouth.
The temporalis muscle is a fan-shaped muscle that elevates and retracts the mandible. It also contributes to side-to-side grinding movements.
