Question

Part C - How an action potential affects Ca2+ movement in a muscle cell The sarcoplasmic reticulum is a specialized form of ER that surrounds each myofibril. The sarcoplasmic reticulum functions to control cytosolic Ca2+ levels in the muscle cell. Changes in cytosolic Ca2+ concentrations couple action potentials to muscle contraction. The concentration of Ca2+ ions in the sarcoplasmic reticulum is typically much higher than the Ca2+ concentration in the cytosol. This concentration gradient is key to the movement of Ca2+ in the muscle cell in response to an action potential. The cycle diagram below shows the sequence of events that affect Ca2+ levels in a muscle cell, beginning with the propagation of an action potential down a T tubule (top of the diagram). Drag the labels to their appropriate locations on the cycle diagram below. Note that SR stands for sarcoplasmic reticulum.

Answer 1

It starts in action potential propagates down to T tubule. It goes to part a where Ca2+channels in SR open. Part b where Ca2+ diffuses out of SR. Part c where cytosolic Ca2+ level rises to part d where Ca2+ diffuses into myofibrils the action potential is completed and goes on to part e where Ca2+ channels in SR dose to part f where Ca2+ level drops to part h where Ca2+ diffuses out of myofibril then back to action potential propagates down T tubules.