generate pulling forces because they are made of two key proteins—one thin, the other thick—that try to slide past each other like interlacing the fingers of your two hands. This contractile action occurs whenever a nerve sends an electrical signal to the muscle, causing tiny projections on the thick filaments to pull against the thin filaments much like a tug-of-war team pulls on a rope. The ratcheting action of each projection exerts a minuscule tug at the cost of a single ATP. Because there are billions of these projections in every muscle, and they keep ratcheting repeatedly, the many
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