USMLE Step 1 Physiology Review 55 09 Myocardial Action (3_3)

USMLE Step 1 Physiology Review 55 09 Myocardial Action (3_3)

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Play USMLE Audio MP3 55 09 Myocardial Action (3_3) Below

Begin 55 09 Myocardial Action (3_3) Transcription

What term describes the period from the rapid upstroke of the action potential to the end of the plateau?

  • Absolute refractory

What is the absolute refractory period?

  • It is the time during which no action potential can be initiated

The absolute refractory period last through what phases?

  • From Phase zero through the end of phase two

Relative to the absolute refractory period, how long does the effective refractive period last?

  • It is slightly longer than the absolute refractive period and extends into phase three

What is the definition for the effective refractive period?

  • It is the period during which a conducted action potential cannot be elicited.

What is the name for the period just following the absolute refractory period when repolarization is almost complete?

  •   This is the relative refractory period.

Can an action potential occur during the relative refractory period ?

  • Yes

What is unusual about the requirement for an action potential to take place during a relative refractory period?

  • More than the usual inward current is required.

Student doctor, please pause the tape and summarize the information discussed since the last summary on Myocardial action.

The first question was about absolute refractory period. Absolute refractory is the period from the rapid upstroke of the action potential to the end of the plateau. The absolute refractory period is the time during which no action potential can be initiated and it lasts from Phase zero through the end of phase two. The effective refractory period last slightly longer than the absolute refractory period and extends into phase three. The effective refractory period is the period during which a conducted action potential cannot be elicited. The period just following the absolute refractory period when repolarization is almost complete is the relative refractory period. An action potential can occur during the relative refractory period but more than the usual inward current is required.

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