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A Band


- Discussion:
    - anisotropic band, the A band appears dark;
    - it is composed of parallel thick and thin filaments;
    - it is composed of interdigitating areas of myosin and actin;

- H Zone:
    - each A band is bisected by light area, or H zone;
    - H zone contains only thick filaments (myosin only);
    - in favorable preparations, the H zone is seen to be crossed in its middle by a thin, dark line, the M line;
    - w/ maximal contraction, sarcomere shortens 20% to 50% of its nl resting length;
    - I band becomes shorter & H zone usually disappears (as thick and thin filaments overlap)