Muscle Cells Need Calcium Pumps
An impulse from a motor neuron causes stimulus of a muscle cell by acetylcholine. In response, the muscle cell allows an influx of sodium ions, which then stimulate a muscle impulse. The muscle cell’s sarcoplasmic reticulum responds to this impulse by becoming more permeable to Ca2+. The diffusion of Ca2+ into the muscle fiber’s cytoplasm allows the Ca2+ to bind to the troponin of the muscle’s thin filament. This binding triggers events with the fiber’s filaments that result in a contraction cycle. When the acetylcholine is decomposed, the membrane’s permeability decreases. The calcium ATPase pumps actively transport the Ca2+ back into the sarcoplasmic reticulum starting the events which relax the muscle.
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