- 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)