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    From Musculoskeletal System

    Hinge Joints
    e.g., elbow, knee
    Achilles Tendon
    Tendon connecting the calf muscle to the heel bone.
    Synchondroses
    Cartilaginous joints where bones are connected by hyaline cartilage.
    Thoracic Vertebrae (T1 - T12)
    Vertebrae in the upper and mid-back (T1-T12).
    Humerus
    Upper arm bone connecting the shoulder to the elbow.
    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.
    Posterior Cruciate Ligament (PCL)
    Knee ligament that stabilizes the joint.
    Gliding (Plane) Joints
    e.g., between carpals
    Patellar Tendon
    Tendon connecting the patella to the tibia.
    Lateral Collateral Ligament (LCL)
    Knee ligament that stabilizes the outer knee.
    Rectus Abdominis
    Abs muscle that flexes the trunk.
    Sternocleidomastoid
    Muscle that rotates and flexes the neck.
    Clavicle
    Collarbone connecting the arm to the body.
    Anterior Cruciate Ligament (ACL)
    Knee ligament that stabilizes the joint.
    Ulna
    Forearm bone on the pinky side.
    Quadriceps
    Rectus Femoris, Vastus Medialis, Vastus Lateralis, Vastus Intermedius.
    Pelvic Floor Muscles
    Muscles that support pelvic organs.
    Gomphoses
    Fibrous joints where a peg fits into a socket (e.g., teeth in jaw).
    Phalanges (14 bones)
    14 bones forming the toes.
    Hamstrings
    Biceps Femoris, Semitendinosus, Semimembranosus.
    Vertebral Column
    Spinal column consisting of vertebrae.
    Coccygeus
    Pelvic floor muscle supporting the coccyx.
    Facial Bones
    Bones forming the structure of the face.
    Syndesmoses
    Fibrous joints where bones are connected by ligaments.
    Mandible
    Lower jawbone that houses the teeth.

    Masseter

    Reviewed by our medical team

    Muscle that elevates the mandible.

    1. Overview

    The masseter is one of the main muscles of mastication and is among the strongest muscles in the human body relative to its size. Located in the lateral jaw region, it plays a critical role in chewing by elevating the mandible (lower jaw). The masseter works in coordination with the temporalis, medial pterygoid, and lateral pterygoid muscles to facilitate complex mandibular movements.

    2. Location

    The masseter is located on the lateral aspect of the face and jaw:

    • Superficially: Lies just beneath the skin and subcutaneous tissue over the posterior cheek.

    • Anteriorly: Bordered by the buccinator muscle and parotid duct.

    • Posteriorly: Lies near the parotid gland and the mandibular ramus.

    • Deep to: The platysma and skin.

    3. Structure

    The masseter is a thick, quadrangular muscle composed of superficial and deep parts:

    • Origin:

      • Superficial part: Zygomatic process of the maxilla and lower border of the anterior two-thirds of the zygomatic arch.

      • Deep part: Posterior third of the zygomatic arch and deep surface of the arch.

    • Insertion:

      • Superficial fibers: Angle and lower lateral surface of the ramus of the mandible.

      • Deep fibers: Upper half of the ramus and the coronoid process of the mandible.

    • Innervation: Mandibular division (V3) of the trigeminal nerve via the masseteric nerve.

    • Blood supply: Masseteric artery (a branch of the maxillary artery).

    4. Function

    The primary actions of the masseter include:

    • Elevation of the mandible: Closes the jaw during mastication (chewing).

    • Protrusion: The superficial part assists in moving the jaw forward.

    • Stabilization: Helps maintain tension in the jaw during clenching or holding objects between the teeth.

    5. Physiological role(s)

    Beyond its role in movement, the masseter contributes to:

    • Mastication efficiency: Provides significant bite force, enabling effective food breakdown for digestion.

    • Facial contouring: Defines the angle of the jaw and contributes to facial shape and aesthetics.

    • Speech and articulation: Stabilizes the mandible during speech and phonation.

    • Protective tension: Activates during reflex jaw closure to prevent damage from foreign objects or trauma.

    6. Clinical Significance

    The masseter is frequently involved in dental, musculoskeletal, and aesthetic conditions:

    • Temporomandibular joint disorders (TMD):

      • Masseter hyperactivity or spasm can contribute to jaw pain, clicking, and restricted movement.

    • Bruxism (teeth grinding):

      • Involuntary clenching or grinding of teeth, especially at night, can lead to masseter hypertrophy and muscle fatigue.

    • Masseteric hypertrophy:

      • Can result in a square jaw appearance; often seen in chronic bruxism or in athletes who use jaw muscles intensively.

      • Botulinum toxin (Botox) is sometimes used to reduce hypertrophy for both functional and cosmetic reasons.

    • Mandibular fracture stabilization:

      • The masseter muscle exerts significant force on the mandible and can displace fractures, influencing surgical planning.

    • Trigger points and myofascial pain:

      • Chronic tension or overuse may lead to localized muscle knots, pain on palpation, and referral pain patterns.

    Did you know? Your bones are constantly being broken down and rebuilt — you have a new skeleton every 10 years.