The action potential propagates along the sarcolemma. as the action potential spreads down the t tubules of the triads, voltage-sensitive tubule proteins change shape. how does the shape change of these proteins lead to contraction?

It permits calcium to leave the sarcoplasmic reticulum and enter the cytosol. During muscle contraction, the binding of acetylcholine initiates an excitatory impulse, which is transmitted to the deep of the muscle via T tubules. T tubules are the invaginations of cell membranes of muscle cells (sarcolemma). When the action potential travel down the t-tubules, they change shape and allow the calcium ions to enter into the sarcoplasm from the sarcoplasmic reticulum.