State of Contraction


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•  Analysis of electron micrographs to find the state of contraction of muscle fibres

The arrangement of myofilaments within a sarcomere give a skeletal muscle fibre a striated appearance

  • A sarcomere has a central darker region (A band) where actin and myosin filaments overlap
  • A sarcomere has peripheral lighter regions (I bands) where actin is present, but not myosin

When muscle fibres contract, actin filaments slide along the myosin, reducing the length of the lighter I bands

  • The movement of the actin filaments also reduces the width of the H zone, however the length of A bands do not change

Changes in Band Lengths with Sarcomere Shortening

Electron Micrographs of Muscle Fibres  (Click for false colour imaging)

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