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Musculoskeletal System key concepts

11 revision pages for Musculoskeletal System, each with the key facts, a memory aid where one helps, and the exam traps.

  1. Biceps brachii as a supinator of the forearm

    The biceps brachii turns the palm upwards (supination) because its tendon attaches to the radial tuberosity, a rough bump on the radius.

  2. Brachialis: the main elbow flexor in any forearm position

    Brachialis is the main elbow flexor (the muscle that bends the arm at the elbow), and because it attaches to the ulna it works in every forearm position.

  3. Erb's palsy and the C5 and C6 roots

    Erb's palsy is damage to the C5 and C6 roots (the parts of the spinal nerves just outside the spinal cord) of the brachial plexus, the arm's nerve network.

  4. Median nerve cut at the wrist: thenar wasting, with palm sensation that can be spared

    A median nerve cut at the wrist paralyses the thenar muscles (the bulk at the base of the thumb), yet lateral palm sensation can be preserved.

  5. Pectoralis major: where it lies and what it does

    Pectoralis major is a fan-shaped muscle on the front of the chest, behind the breast, that adducts (pulls the arm in) and medially rotates (turns it inwards) the humerus.

  6. Radial head and forearm rotation

    The head of the radius spins against the ulna, so the radius turns around it for pronation (palm down) and supination (palm up).

  7. Rhomboids: scapular retraction and dorsal scapular nerve

    The rhomboids are upper back muscles that retract the scapula (draw the shoulder blades together) and are supplied by the dorsal scapular nerve, a motor nerve from C5.

  8. Rotator cuff tears: supraspinatus and weak initiation of abduction

    Rotator cuff tears damage any of four muscles that hold the humerus in its shoulder socket; a tear of supraspinatus, the cuff muscle that starts abduction, classically weakens that movement.

  9. Serratus anterior and winged scapula

    Injury to the long thoracic nerve can weaken serratus anterior, the muscle that holds the scapula against the chest wall, so the medial border of the scapula lifts away.

  10. Supraspinatus versus deltoid in abduction

    In standard anatomy teaching, supraspinatus starts lifting the arm out to the side over about the first 15 degrees, and after that the deltoid is the main mover.

  11. Trapezius and spinal accessory nerve injury

    The trapezius, which lifts the scapula in a shrug, is supplied by the spinal accessory nerve, so injury to that nerve weakens the shrug and drops the shoulder.

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