Jul 28, 2017
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Pre-Health (Field Undecided)
In EK 9E Biology 2: Systems it states that

"The action potential of cardiac muscle exhibits a plateau after depolarization. The plateau is created by slow voltage-gated calcium channels, which allow calcium to enter and maintain the inside of the membrane at a positive potential difference. As a result, repolarization of cardiac muscle is slower and more frequent than that of skeletal muscle."

I'm not sure how they arrived at the conclusion that cardiac muscle repolarization is more frequent than repolarization of skeletal muscle and I'm not sure I understand what they mean.

Do they mean that the cardiac muscle spends more time in a depolarized state?

I would assume that if the repolarization frequency is higher, the depolarization frequency must also be higher, so are they saying cardiac muscle depolarization is more frequent than skeletal muscle? (which is understandable if the heart is pumping constantly)

Thanks!
 

theonlytycrane

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The goal of the heart is to fill the atrial and ventricle chambers in cadence to pump blood throughout the body. If the heart pumps too fast, the chambers can't fill with blood adequately because there isn't enough time to do so.

The first part of the action potential involves an influx of Na+ ions (depolarization). Next comes an efflux of K+ ions out of the cell (repolarization). Instead of repolarizing as soon as possible, though, cardiac muscle has voltage-gated calcium channels that let Ca2+ ions into the cell while K+ leaves. This creates a delay in the action potential propagation, allowing extra time for the heart chambers to fill with blood. So repolarization of cardiac muscle takes longer and needs to happen more since voltage-gated calcium channels exist here.
 
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OP
R
Jul 28, 2017
33
2
Status
Pre-Health (Field Undecided)
The goal of the heart is to fill the atrial and ventricle chambers in cadence to pump blood throughout the body. If the heart pumps too fast, the chambers can't fill with blood adequately because there isn't enough time to do so.

The first part of the action potential involves an influx of Na+ ions (depolarization). Next comes an efflux of K+ ions out of the cell (repolarization). Instead of repolarizing as soon as possible, though, cardiac muscle has voltage-gated calcium channels that let Ca2+ ions into the cell while K+ leaves. This creates a delay in the action potential propagation, allowing extra time for the heart chambers to fill with blood. So repolarization of cardiac muscle takes longer and needs to happen more since voltage-gated calcium channels exist here.
Does the calcium pump in the sarcoplasmic reticulum play a large part in the repolarization (along with the Na+/K+ pump and K+ leak channel)?
 
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OP
R
Jul 28, 2017
33
2
Status
Pre-Health (Field Undecided)
Can you clarify your question?
Reploarization of neurons involves the sodium-potassium pump pumping 2K+ in and 3Na+ out of the cell and the potassium leak channel allowing the K+ that were pumped in to leak out to create a negative membrane potential. In the neurons, the K+ leak channel is responsible for almost al of the repolarization. In order to repolarize muscle cells, I would think that all of that Ca2+ that was released from the sarcoplasmic reticulum would have to be pumped back into the sarcoplasmic reticulum.
 
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