sentences:  A stimulus, in the form of positively charged current, is transmitted from the neuromuscular junction down the length of the T tubules, activating dihydropyridine receptors (DHPRs).Their activation causes 1) a negligible influx of calcium and 2) a mechanical interaction with calcium-conducting ryanodine receptors (RyRs) on the adjacent SR membrane.Activation of RyRs causes the release of calcium from the SR, which subsequently initiates a cascade of events leading to muscle contraction.