Order the following events of excitation and excitation-contraction coupling. Put 1 by the first event, 2 by the second, and so on.
____The motor end plate generates an end-plate potential.
____The action potential spreads along the T-tubules, SR Ca2+ channels are pulled open, and Ca2+ flood the cytosol.
____Acetylcholine binds to receptors on the motor end plate, and ligand-gated ion channels open.
____Ca2+ bind troponin, which allows tropomyosin to move away from the actin active site, initiating a contraction cycle.
____The action potential propagates through the sarcolemma and dives deeply into the cell along the T-tubules.