According to the sliding filament theory, what is the initial action in a muscle contraction?
A) Troponin is freed and prevents actin and myosin from reacting with each other.
B) Calcium binds to troponin, which causes the release of actin and myosin binding sites.
C) Actin and myosin molecules react with each other sliding along the filament and making it shorter.
D) Muscle filament relaxes or slides back to the resting position.
C
Feedback:
Actin and myosin molecules react with each other again and again, sliding along the filament and making it shorter. This is a contraction of the muscle fiber according to the sliding filament theory. As the calcium is removed from the cell during repolarization of the muscle membrane, the troponin is freed and once again prevents the actin and myosin from reacting with each other. The muscle filament then relaxes or slides back to the resting position. Muscle tone results from a dynamic balance between excitatory and inhibitory impulses to the muscle.
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