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The human jaw, or mandible, is moved by a group of muscles called the muscles of mastication. These muscles are associated with the movement of the jaw, or temporomandibular joint, and develop from the first pharyngeal arch. There are four primary muscles of mastication: the masseter, temporalis, medial pterygoid, and lateral pterygoid. The medial pterygoid muscle is responsible for the elevation, protrusion, and horizontal movements of the jaw.
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What You'll Learn
- The masseter muscle is the most powerful muscle of mastication
- The medial pterygoid muscle aids jaw elevation and protrusion
- The temporalis muscle is responsible for jaw closure
- The lateral pterygoid muscle is responsible for jaw opening
- The mandibular nerve innervates the four main muscles of mastication
The masseter muscle is the most powerful muscle of mastication
The masseter muscle is one of the primary muscles of mastication, responsible for the elevation of the mandible and some protraction. The masseter is a powerful muscle that originates from the zygomatic arch and inserts along the angle and lateral surface of the mandibular ramus. It is a fan-shaped muscle that fills the temporal fossa, with anterior fibres that are vertically oriented, mid fibres with an oblique orientation, and posterior fibres that are horizontally oriented. The major function of the masseter muscle is to elevate the jaw bone, bringing the teeth together in a chewing motion. This muscle works in conjunction with two other jaw-closing muscles, the temporalis and the medial pterygoid, to close the jaw.
The masseter muscle is also responsible for the protrusion movement, which involves moving the mandible forward through the contraction of its superior part. The deep fibres of the masseter muscle function to retract the mandible, while the superficial fibres function to protrude the mandible. The masseter muscle can become enlarged in patients who habitually clench or grind their teeth, a condition known as bruxism. This enlargement is usually bilateral but can be unilateral, and it can lead to asymmetry of the face due to unequal enlargement of the muscles. Bruxism is characterised by involuntary teeth clenching or grinding and can cause extremely powerful forces on the teeth, leading to tooth wear and destruction.
The masseter muscle is innervated by the masseteric nerve, a branch of the mandibular nerve (V3) of the trigeminal nerve. The mandibular nerve carries both sensory and motor fibres. The blood supply to the masseter muscle comes from the masseteric artery, a branch of the maxillary artery. Dysfunction of the masseter muscle can result in pain, difficulty chewing, or swelling around the jaw and face, which can lead to TMD and, in serious cases, difficulty speaking.
The masseter muscle is a powerful muscle of mastication, responsible for the elevation and protrusion of the mandible, and it plays a crucial role in the chewing motion. Its dysfunction can lead to various issues, including pain and difficulty with oral functions.
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The medial pterygoid muscle aids jaw elevation and protrusion
The medial pterygoid muscle is a major elevator of the jaw and is located in the infratemporal fossa, lying deep to the masseter and temporalis muscles. It has two heads: a superficial head and a deep head. Both heads insert on the inner surface of the mandible, creating an axis for a strong pull of this bone. The outer surface of the muscle lies against the inner surface of the mandible, from which it is separated by the lateral pterygoid muscle, sphenomandibular ligament, maxillary artery, mandibular nerve, and its lingual and inferior alveolar branches.
The medial pterygoid muscle assists in jaw elevation and protrusion. Unilateral contraction of the medial pterygoid muscle causes rotation of the mandible, while bilateral contraction elevates and protrudes it. Alternating contraction of the medial pterygoid and lateral pterygoids causes side-to-side movements of the mandible. This movement is observable during functional and parafunctional lateral excursive movements, such as the chewing stroke, masticating, and clenching.
The medial pterygoid muscle also has a role in the horizontal movements of the jaw. It acts in synergy with other masticatory muscles, and these actions facilitate chewing and food grinding between the maxillary and mandibular teeth. The medial pterygoid muscle is one of the four muscles of mastication, along with the lateral pterygoid muscle, masseter, and temporalis.
The lateral pterygoid muscle is the only muscle of mastication that assists in depressing the mandible (opening the jaw). It is active during mastication and mandibular movements, including protrusion (forward movement of the mandible), abduction (depression of the mandible), and mediotrusion (mandibular condyle movement towards the midline). The medial pterygoid muscle, on the other hand, closes the jaw.
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The temporalis muscle is responsible for jaw closure
The temporalis muscle is a broad, fan-shaped muscle located on each side of the skull. It is a muscle of mastication, meaning it is involved in the process of chewing. The muscle fills the temporal fossa, which is a shallow depression on the lateral side of the head, and covers much of the temporal bone. The temporalis muscle is responsible for jaw closure, elevating the jaw and closing the mouth. It also plays a role in maintaining proper alignment of the temporomandibular joint (TMJ).
The temporalis muscle works in conjunction with other jaw muscles, including the masseter, medial pterygoid, and lateral pterygoid, to enable smooth and powerful biting. Its positioning allows for significant force generation during jaw closure, while its posterior fibres aid in retracting the mandible. The muscle's function can be influenced by head posture, with a forward head position often increasing tension as the jaw may have to clench to maintain occlusion.
Overuse or strain of the temporalis muscle can lead to headaches, jaw pain, and toothache-like pain. Conditions such as bruxism, the habitual grinding of teeth or clenching of the jaw, can result in overwork of the muscle and subsequent pain. In addition, a myotendinous rupture of the temporalis muscle can occur during a seizure due to extreme clenching of the jaw.
The temporalis muscle may be involved in reconstructive surgery of the mouth. During pterional craniotomy, incisions are often chosen based on the ease of reattaching the muscle after the bone fragment is replaced. Understanding the anatomy and function of the temporalis muscle is crucial for maintaining jaw health and treating related disorders.
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The lateral pterygoid muscle is responsible for jaw opening
The lateral pterygoid muscle is a short, thick, fan-shaped muscle with two heads: the superior (upper) and inferior (lower). The muscle is located deep to the temporalis and masseter muscles, spanning between the sphenoid bone and the temporomandibular joint (TMJ).
The lateral pterygoid is one of the four main muscles of mastication, along with the medial pterygoid, temporalis, and masseter muscles. These muscles act upon the TMJ to enable chewing and biting. The lateral pterygoid contributes to this function by protruding and depressing the mandible when contracting bilaterally and by rotating the mandible when contracting unilaterally.
The superior head of the lateral pterygoid arises from the infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone. The inferior head, which is much wider than the superior head, arises from the lateral surface of the lateral pterygoid plate of the sphenoid bone. Fibers from both heads converge and form a tendon that inserts into the pterygoid fovea of the neck of the condylar process of the mandible, along with the articular capsule and disc of the TMJ.
The lateral pterygoid muscle is innervated by a branch of the anterior division of the mandibular nerve, and its blood supply comes from the pterygoid branch of the second part of the maxillary artery.
The function of the lateral pterygoid muscle is primarily associated with jaw opening. The inferior head is active during jaw opening, jaw protrusion, and contralateral jaw movements, while the superior head is active during jaw closing, jaw retrusion, and ipsilateral jaw movements. Bilateral contraction of the left and right lateral pterygoid muscles results in translation and rotation within both TMJs, leading to the protrusion and depression of the mandible.
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The mandibular nerve innervates the four main muscles of mastication
The four main muscles of mastication are the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles. These muscles are responsible for the movement of the jaw (mandible) during chewing. They enable cardinal mandibular movements such as elevation, depression, protrusion, retraction, and side-to-side motion, assisting in the grinding of food and approximating the teeth.
The mandibular nerve, a division of the trigeminal nerve (CN V3), innervates these four primary muscles of mastication. The mandibular nerve is the largest and most inferior division of the trigeminal nerve, exiting the skull through the foramen ovale of the greater wing of the sphenoid bone. It carries both sensory and motor fibres, with the motor fibres innervating the muscles of mastication.
Each of the four main muscles of mastication receives innervation from specific branches of the mandibular nerve. The temporalis muscle, a fan-shaped muscle originating from the temporal fossa, is innervated by the deep temporal branches of the mandibular nerve. It functions to elevate the mandible and contributes to side-to-side grinding movements.
The medial pterygoid muscle, a thick rectangular muscle with two heads, receives innervation from the medial pterygoid nerve, a division of the mandibular nerve. This muscle assists in jaw elevation, protrusion, and horizontal movements. The lateral pterygoid muscle, on the other hand, is innervated by the lateral pterygoid nerve, another division of the mandibular nerve. It is responsible for causing depression of the mandible, assisting with protrusion, and enabling side-to-side movement.
The masseter muscle, a strong quadrangular muscle covering the lateral aspect of the mandible, is innervated by the masseteric nerve, a branch of the mandibular nerve. Its primary function is to elevate the mandible and approximate the teeth.
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Frequently asked questions
The muscles that are associated with jaw movement are the masseter, temporalis, medial pterygoid, and lateral pterygoid.
The masseter muscle is the most powerful muscle of mastication and is responsible for closing the mandible.
The medial pterygoid muscle is responsible for the elevation, protrusion, and horizontal movements of the jaw.
The masseter muscle can be tested by having the patient clench their jaw and evaluating the volume and firmness of the muscles.
