Striated muscle. Coloured transmission electron micrograph (TEM) of a longitudinal section through striated muscle. The arrangement of the muscle's myofibrils produces the regular banding pattern. The wide A bands (yellow) are bisected by narrow H bands (red), which contain thick filaments of the protein myosin. The I bands (brown) contain thin filaments of the protein actin. According to the widely-accepted sliding filament theory, it is these thick and thin filaments that slide past one another during contraction, causing the H and I bands to narrow. Magnification: x16,300 when printed 10 centimetres high.
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