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Old 04-15-2012
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MusculoSkeletal A Bands In Muscle Contraction

Why do the A Bands remain the same in muscle contraction?

If the distance between the Z lines is decreasing, shouldn't the amount of overlap between actin and myosin increase?

I'm completely lost. Any help would be appreciated.
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Old 04-15-2012
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A band represents myosin itself, it doesn't contract
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This might help you remember it
Skeletal Muscle bands and zones

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This is why. The myosin filaments (thick filaments / A band) don't actually get smaller. They simply overlap with the actin filaments (thin filaments / I band). Since we're seeing this through an electron microscope, we'll be seeing a much smaller region with ONLY actin filaments, meaning the I band will get smaller while the A band stays the same size. Here's a picture to explain what I mean.

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Thanks a million. Muscle contraction is MUCH clearer now.
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