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Home Q & A Board Biology-Related Homework Help Anatomy and Physiology
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kweigl1 kweigl1
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13 years ago
I need help with these 2 questions, from PhysioEX 8.0, Cardiovascular Physiology & will appreciate any help you can offer.
Thank You In Advance  Slight Smile


6. Explain why the SA node generates action potentials at a frequency of approximately 100 beats per minute even though the average resting heart rate is 70 beats per minute?


9. When the heart is externally stimulated just after the start of the contraction cycle, why does this have no affect on heart rate?
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9. When the heart is externally stimulated just after the start of the contraction cycle, why does this have no affect on heart rate

This is because once a contraction has started, the action potential has already fired, stimularing the muscle fibers. Once they are fired in the heart, there is: depolarization, followed by a plateau, a rapid repolarization, and then a small refractory period. It is only after the refractory period can the heart fire again, because the Na+ and K+ balances must return to the state they were just before depolarization.
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biolovebiolove
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