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muscles

Major Muscle Groups and Their Attachments

Masseter Muscle

  • Superior Attachment: Zygomatic arch

  • Inferior Attachment: Angle and ramus of mandible

  • Action: Elevates and protracts the mandible; it is the prime mover of elevation, crucial for chewing.

Sternocleidomastoid Muscle

  • Superior Attachment: Mastoid process of temporal bone

  • Inferior Attachment: Manubrium of sternum & sternal end of clavicle

  • Action: Bilaterally flexes the neck; unilaterally rotates the head to the opposite side, important for head movement.

Rectus Abdominis Muscle

  • Superior Attachment: Xiphoid process of sternum

  • Inferior Attachment: Superior surface of pubis near symphysis

  • Action: Flexes the vertebral column and compresses the abdominal wall, essential for posture and core stability.

Trapezius Muscle

  • Superior Attachment: Occipital bone & ligamentum nuchae

  • Inferior Attachment: Clavicle, acromion, spine of scapula

  • Action: Elevates, retracts, depresses, and rotates the scapula, playing a key role in shoulder movement.

Deltoid Muscle

  • Proximal Attachment: Clavicle, acromion, spine of scapula

  • Distal Attachment: Deltoid tuberosity of humerus

  • Action: Abducts the arm; anterior fibers flex/medially rotate, while posterior fibers extend/laterally rotate the arm.

Major Actions and Movements of Muscles

Elbow Movements

  • Flexion (Bending): Prime movers include Biceps brachii, Brachialis, and Brachioradialis.

  • Extension (Straightening): Prime movers include Triceps brachii and Anconeus.

Shoulder Movements

  • Abduction: Main mover is Deltoid (middle fibers); Supraspinatus initiates the first 15°.

  • Adduction: Pectoralis major, Latissimus dorsi, and Teres major are key players.

Hip Movements

  • Flexion: Strongest muscles are Iliopsoas (iliacus + psoas major), Rectus femoris, and Sartorius.

  • Extension: Gluteus maximus and Hamstrings (biceps femoris, semitendinosus, semimembranosus) are involved.

Knee Movements

  • Extension: Quadriceps group (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) are the prime movers.

  • Flexion: Hamstrings (biceps femoris, semitendinosus, semimembranosus) and Gastrocnemius assist.

Common Injuries and Ligament Functions

Common Musculoskeletal Injuries

  • Unhappy Triad: Involves ACL, medial meniscus, and MCL injuries, often occurring in sports.

  • Shoulder Separation: Injury to the acromioclavicular joint, typically from falls or impacts.

Ligament Functions

  • ACL (Anterior Cruciate Ligament): Prevents anterior tibial translation, crucial for knee stability.

  • PCL (Posterior Cruciate Ligament): Prevents posterior tibial translation, also important for knee stability.

Ankle and Disc Injuries

  • Ankle Inversion Sprain: Tears lateral ligaments, with the anterior talofibular ligament being the most commonly affected.

  • Disc Herniation: Occurs when the nucleus pulposus protrudes, compressing spinal nerves, leading to pain and mobility issues.