Review Note

Last Update: 01/28/2025 10:35 PM

Current Deck: PHYSIOLOGY::exam one

Published

Describe the phases

Phase 0 = Na+ enters via fast Na+ channels to generate upstroke
Phase 1 = efflux of K+ through voltage-gated channels generates early and partial repolarization
Phase 2 = during plateau, net influx of Ca2+ through Ca2+ channels (L-type Ca channels - "L" stands for long duration, these are voltage-gated channels) is balanced by efflux of K+
Phase 3 = efflux of K+ through leak and voltage-gated channels now predominate
Phase 4 = efflux of K+ through leak channels slightly exceeds the influx of K+ through these same channels
Refractory period: cardiac muscle has a refractory period after excitation during which it cannot be re-excited. This lasts about half a second, followed by a relative refractory period in which a stronger than normal stimulation is required to excite the heart tissue

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