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SARCOMERE CONTRACTION
Large-scale muscle contraction
requires the coordinated flexion of many myosin
heads interacting with many active sites on the
actin filaments.
As long as the muscle fiber
is stimulated, the myosin heads will repeat the
cycle:
Imagine the myosin thick filament
as two people, back to back, in the middle of
the sarcomere. Each person is pulling on an actin
filament attached to the Z lines that define the
opposite ends of the sarcomere. As they pull the
rope in, hand over hand, the two Z lines are drawn
closer, and the sarcomere contracts (the I band
and the H zone both get thinner).
Now imagine thousands upon thousands
of sarcomeres lined up in a myofilament and bundled
together into muscle fibers. The effect of each
sarcomere contracting just a small distance is
multiplied thousands of times, resulting in the
muscle contracting a long distance.
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