Sliding Filament Theory

What is the first step of the sliding filament theory?

The Stimulus - A nerve impulse travels down the motor neuron to the muscle fiber, then along the sarcolemma and down the T-tubules.

What happens during calcium release in muscle contraction?

The impulse reaches the sarcoplasmic reticulum, which releases calcium ions (Ca²⁺) into the muscle fiber, exposing active sites on the actin filaments.

What is cross-bridge formation?

Myosin heads attach to the exposed active sites on actin filaments, forming connections called cross-bridges.

Describe the power stroke in muscle contraction.

Using 1 ATP molecule, the myosin head pivots and pulls the actin filament toward the center (M-line), like a tiny rowing motion.

What happens during the reset phase of muscle contraction?

Another ATP molecule is used to detach the myosin head from actin and cock it back to its original position.

What is the final result of the sliding filament theory?

As myosin pulls actin filaments, the Z-lines move closer together and the sarcomere shortens, leading to muscle contraction.

Why is it called the 'sliding' filament theory?

Because the filaments slide past each other like telescoping parts without changing their length.

How many ATP molecules are needed for one complete contraction cycle?

2 ATP molecules - 1 for the power stroke and 1 for resetting the myosin head.