The Steps of the Sliding Filament Theory

By, Anthony Palma, Zachary Trawinski, Tyler French, Haley Felemyng, Genevieve Peltot

What causes the filaments to slide?

Myosin heads protrude ends of thick filaments. They are activated by the nervous system and they are attached to sites on the thin filaments, which causes sliding to occur.

Cross bridges attach and detach several times during contraction creating tension that helps pull thin filaments toward the center of the sarcomere.

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Step One

When a muscle is relaxed proteins forming part of the actin myofilaments prevents myosin binding. When a muscle is excited, calcium ions are released from the intracellular storage areas, which are located in the sarcoplasmic reticulum.

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Step two

The influx of calcium ions triggers exposure of binding sites on actin which allows myosin head to attach. Then myosin head immediately start seeking out binding sites. The myosin heads are then set in a cocked position.

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Step Three

Physical attachment of myosin and actin causes the myosin to pivot toward the sarcomere. When the action ends calcium ions are reabsorbed into the SR storage areas. The regulatory proteins go back into their regular shape and position and this allows blockage of myosin from binding into the thin filaments. Because of the detachment the muscle cell relaxes and goes back to its original length.

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Diagram of Sliding Filament Theory