Excitation-Contraction Coupling is Accomplished by Calcium Ions

Changes in Ca2+ permeability are shown in the bottom panel of Fig. 7. The initial depolarization of the membrane causes Ca2+ conductance to increase in a voltage-dependent manner. Unlike the sodium channels, the calcium channels are slow to close and there is a sustained increase in Ca2+ conductance, which maintains the plateau of the cardiac action potential. Another factor contributing to the plateau of the cardiac action potential is the change in K+ conductance (Fig. 7). At rest, the K+ conductance of cardiac cells is high, just as it is in nerve and skeletal muscle cells. The similarity, however, ends here. When nerve and muscle cells repolarize, a transient increase is observed in K+ conductance over the resting value, which quickly terminates the action potential and momentarily hyperpolarizes the cell. In contrast, in cardiac muscle K+ conductance decreases with depolarization (Fig. 7), and during repolarization K+ conductance simply returns to its phase 4 value. That is why cardiac muscle has no hyperpolarizing afterpotential. We should mention that there are many different types of potassium channels in the cardio-myocyte and their individual functions in controlling K+ conductance through the action potential are complex. A detailed description of these is beyond the scope of this chapter.

Get Rid of Gallstones Naturally

Get Rid of Gallstones Naturally

One of the main home remedies that you need to follow to prevent gallstones is a healthy lifestyle. You need to maintain a healthy body weight to prevent gallstones. The following are the best home remedies that will help you to treat and prevent gallstones.

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