Explain the steps of excitation-contraction coupling:
1) a wave of action potential spreads from the motor end plate in all directions to the t-tubules, which are linked to Ca channels in the terminal cisternea of the sarcoplasmic reticulum.
2) Ca channels open in the sarcoplasmic reticulum (SR) and flow down the concentration gradient to the cytosol.
3) Ca binds to the troponin in the thin filament (actin). The troponin-tropomyosin complex changes shape, exposing the active sites on the actin filaments.
4) ATP initiates contraction by binding to myosin head. Myosin ATPase hydrolyzes aTP into ADP and phosphate, releasing the energy needed to cock it's head forming a cross bridge.
5) Myosin releases the ADP and P, and flexes into a bent position, tugging (power stroke) the thin filament along.
6) APT binds to the myosin, breaking the cross bridge, and repeating the process.