Plateau phase of ventricular muscle is d/t opening of:
Correct Answer: Ca2+-Na+ channel
Description: Ans: C (Ca2+-Na+ channel) Guyton 11th/ 117: WritesCardiac muscle has three types of membrane ion channels that play important roles in causing the voltage changes of the action potential. They are (1) fast sodium channels, (2) slow sodium-calcium channels, and (3) potassium channels/* Opening of the fast sodium channels gfor a few lO.OOOths of a second is responsible for the rapid upstroke spike of the action potential observed in ventricular muscle, because of rapid influx of positive sodium ions to the interior of the fiber.Then the "plateau '' of the ventricular action potential is caused primarily by slower opening of the slow sodium- calcium channels1* which lasts for about 0.3 second.Ta2+ influx through more slowly opening of Ca2+ channel produces the plateau phase - Ganong 23nd/491Finally, opening of potassium channels allows diffusion of large amounts of positive potassium ions in the outward direction through the fiber membrane and returns the membrane potential to its resting level
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