How to Summarize the Sliding Filament Theory
The sliding filament theory explains how your muscles contract. The theory was put forth in 1954 when researchers observed changes in the sarcomere, the contractile unit of muscle. To understand the sliding filament theory it is helpful to have an understanding of the microscopic muscular anatomy. There are hundreds of sarcomeres in each muscle fiber and within each sarcomere there are contractile proteins, known as filaments. There is the thick filament, myosin, and the thin, rope-like filament, actin. These filaments slide over top of each other, which causes the muscle to shorten, producing a forceful contraction.
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Explain that your muscle cell is depolarized by a signal sent from the brain.
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Explain that depolarization causes the sarcoplasmic reticulum — a sack within each sarcomere — to release calcium and prepares the other components of the muscle fiber for action.
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Describe the action of the calcium binding to the thin filament, actin, which causes the actin to turn and expose its myosin binding site.
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Tell your audience that myosin and actin bind and pull together to cause muscle shortening. This uses up the stored ATP, the cellular energy source, that was attached to the myosin.
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Explain that another ATP molecule must attach to myosin. For contraction to continue, ATP is hydrolyzed to produce the energy necessary to sustain the contraction.
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Explain that once the contraction signal from the brain runs out, ATP stops being hydrolyzed and actin and myosin detach from each other.
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Describe the cycle ending when calcium molecules are taken up again by the sarcoplasmic reticulum.
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