Muscle Structure

    Cards (8)

    • Muscle cells fuse together to form a myofibril and share nuclei and cytoplasm (sarcoplasm), many mitochondria and endoplasmic reticulum (sarcoplasmic reticulum).
    • Myofibrils bundle together with a shared membrane called sarcomella that has inward-folds called T-tubules so ions can enter the myofibrils. This forms a muscle fibre.
    • Muscle fibres bundle together to form a fascicle.
    • A muscle is made of:
      • Bundle of fascicles
      • Surrounded by connective tissue (perimysium)
      • With a shared outer wall (epimysium)
    • Myofibrils have a striped appearance due to the presence pf regular repeating units called sarcomeres. Each sarcomere is a contracting unit.
    • Myofibrils contain 2 proteins:
      • Actin which is made of thin filaments.
      • Myosin which is made of thick filaments.
    • The arrangement of myofibril proteins give the sarcomeres their characteristic banding pattern.
    • Muscle Structure:
      • I Band: only actin
      • Z Line: centre of I band
      • Z-to-Z: sarcomere
      • A Band: where any myosin is present
      • H Zone: only myosin (no overlap)