Sliding filaments
A band
H zone
I band
H zone gone
Sarcomere (Z disc to Z disc)
thin filament
thick filament
Filaments keep their length
Myofibril (three sarcomeres)
1
Relaxed
Wide I bands and H zone; heads not attached
2
Heads grab and pull
Pulled towards the M line from both ends
3
Z discs move closer
I bands and H zone narrower; A band unchanged
4
Fully contracted
Thin filaments meet near the M line
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