Sliding Filament Theory

Card 1

Front: What is the first step of the sliding filament theory?

Back: The Stimulus - A nerve impulse (action potential) travels down the motor neuron to the muscle fiber, then along the sarcolemma and down the T-tubules.

Card 2

Front: What happens during calcium release in muscle contraction?

Back: The impulse reaches the sarcoplasmic reticulum, which releases calcium ions (Ca²⁺) into the muscle fiber. Calcium exposes active sites on the actin filaments that are normally blocked.

Card 3

Front: What is cross-bridge formation?

Back: Myosin heads (rounded extensions on myosin filaments) attach to the exposed active sites on actin filaments, forming connections called cross-bridges.

Card 4

Front: Describe the power stroke in muscle contraction.

Back: Using 1 ATP molecule, the myosin head pivots and pulls the actin filament toward the center (M-line). This is like a tiny rowing motion where the myosin head "rows" the actin filament.

Card 5

Front: What happens during the reset phase of muscle contraction?

Back: Another ATP molecule is used to detach the myosin head from actin. The myosin head "cocks back" to its original position, ready to attach again. This cycle repeats rapidly.

Card 6

Front: What is the final result of the sliding filament theory?

Back: As myosin pulls actin filaments toward the center, the Z-lines move closer together and the sarcomere shortens. The filaments themselves don't change length - they slide past each other, causing the entire muscle to contract.

Card 7

Front: Why is it called the "sliding" filament theory?

Back: Because the filaments don't actually get shorter - they slide past each other like telescoping parts.

Card 8

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

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