Q:

The following is/are true concerning the physiology of arrhythmias:

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The following is/are true concerning the physiology of arrhythmias:


  1. A physical or electrical stimulus causes sodium fast channels and calcium slow channels to open
  2. During the effective refractory period, only the slow calcium channels are closed
  3. Rapid repolarization follows potassium egress from the cell
  4. Extracellular hypokalemia increases sodium channel size increasing automaticity
  5. Catecholamines increase outward potassium flow from myocytes

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a. A physical or electrical stimulus causes sodium fast channels and calcium slow channels to open

c. Rapid repolarization follows potassium egress from the cell

d. Extracellular hypokalemia increases sodium channel size increasing automaticity

Physical or electrical stimuli cause sodium fast channels and calcium slow channels to open. During the effective refractory period, both slow calcium channels and fast sodium channels are closed and the myocardium cannot be excited. Then potassium channels reopen, allowing potassium out, and rapid repolarization occurs. Extracellular hypokalemia increases transmembrane potassium gradient and sodium channel size increasing automaticity. Catecholamines decrease outward potassium flow from myocytes enhancing automaticity. 

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