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    From Musculoskeletal System

    Rotator Cuff Muscles
    Supraspinatus, Infraspinatus, Teres Minor, Subscapularis.
    Sesamoid Bones
    e.g., patella, some found in hands/feet.
    Extensor Tendons
    Tendons that help extend the fingers and toes.
    Flexor and Extensor Groups
    Muscles responsible for flexing and extending the hand and wrist.
    Coccygeus
    Pelvic floor muscle supporting the coccyx.
    Tarsals (7 bones)
    7 ankle bones.
    Syndesmoses
    Fibrous joints where bones are connected by ligaments.
    Hinge Joints
    e.g., elbow, knee
    Sternocleidomastoid
    Muscle that rotates and flexes the neck.
    Sutures (in the skull)
    Fibrous joints between skull bones.
    Coracoacromial Ligament
    Ligament that connects the acromion to the coracoid process.
    Anterior Longitudinal Ligament
    Spinal ligament running along the front of the vertebral column.
    Posterior Cruciate Ligament (PCL)
    Knee ligament that stabilizes the joint.
    Glenohumeral Ligaments
    Shoulder ligaments that stabilize the shoulder joint.
    Triceps Brachii
    Muscle responsible for elbow extension.
    Sartorius
    Longest muscle in the body responsible for hip flexion.
    Rotator Cuff Tendons
    Tendons of the rotator cuff muscles.
    Trapezius
    Muscle responsible for moving, rotating, and stabilizing the scapula.
    Temporalis
    Muscle involved in closing the jaw.
    Carpals (8 bones)
    8 wrist bones.
    Zygomaticus
    Muscle that raises the corners of the mouth.
    Acromioclavicular Ligament
    Ligament that connects the acromion to the clavicle.
    Palatine Bones
    Bones forming part of the hard palate and nasal cavity.
    Medial Collateral Ligament (MCL)
    Knee ligament that stabilizes the inner knee.
    Synchondroses
    Cartilaginous joints where bones are connected by hyaline cartilage.

    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? Bones are living tissue that is constantly remodeling and repairing itself.