Cardiac Action Potential Flashcards
What determines the resting membrane potential
conductance to K+
approaches K+ equilibrium potential
Inward current ____ the membrane potential
depolarizes;
brings in + charge
OUtward current ____ the membrane potential
hyperpolarizes
pumps out + charge
Resting membrane potential of ventricles, atria and purkinje system
- 90 mV (approaches K+ equilibrium potential)
ventricles, atria and purkinje system
Phase 0
upstroke of action potential
ventricles, atria and purkinje system
Phase 0 is caused by ____
transient increase in Na+ conductance
inward Na+ current until approaches Na+ equilibrium potential at peak of AP
ventricles, atria and purkinje system
Phase 1 is the ____
brief period of initial repol
ventricles, atria and purkinje system Phase 1 (Initial repol) is caused by
outward current (by K+ out and decr Na+ in)
ventricles, atria and purkinje system
Phase 2 is the ___
plateau of the action potential
ventricles, atria and purkinje system Phase 2 (plateau) is caused by \_\_\_
transient incr in Ca2+ conductance (inward CA2+) and incr K+ out
outward = inward current
ventricles, atria and purkinje system
Phase 3 is the ____
repolarization
ventricles, atria and purkinje system
Phase 3 is caused by ___
decr Ca2+ inward, incr K+ outward
outward > inward
hyperpolarizes back toward K+ equilibrium potential
ventricles, atria and purkinje system
Phase 4 is the ___
resting membrane potential
ventricles, atria and purkinje system
Phase 4 is caused by ___
inward and outward currents equal
Vm approaches the K+ equilibrium potential
What is the SA node?
pacemaker of the heart
____ has an unstable resting potential and exhibits phase 4 depolarization
SA node
Latent pacemakers are ___
AV node and His-Purkinje systems
What are latent pacemakers
exhibit automaticity and override SA node if it is suppressed
Order of rate of phase 4 depolarization
SA node > AV node > His-Purkinje
SA node
Phase 0 is the ___
upstroke of the action potential
SA node
What causes phase 0
incr in Ca2+ conductance (inward Ca2+ current) towards Ca2+ equilibrium potential
SA node
Phase 1 and 2
NO PHASE 1 AND 2 IN SA NODE AP
SA node
Phase 3 is the ___
repolarization
SA node
What causes phase 3
incr in K+ conductance (outward K+) —> repolarization of membrane potnetial
SA node
phase 4 is the ____
slow depolarization
SA node
What causes phase 4
pacemaker activity of SA node
incr Na+ conductance (inward Na+)
turned on by repolarization
AV node
Upstroke of AP is due to
inward Ca2+ current (like SA node)
What is conduction velocity
time for excitation to spread throughout cardiac tissue
what does conduction velocity depend on
size of inward current during upstroke of AP (larger inward current, higher conduction velocity)
conduction velocity is fastest in ___ and slowest in ___
fastest in Purkinje
slowest in AV node for ventricular filling before ventricular contraction
what is excitability
ability of cardiac cells to initiate AP in response to inward, depolarizing current
What is absolute refractory period
from upstroke of AP and ends after plateau
NO AP CAN BE INITIATED EVER
what is effective refractory period
conducted action potential cannot be elicited
slightly longer than the absolute refractory
what is the relative refractory period
after absolute refractory period when repol almost complete
when an AP can be elicited but more than usual inward current required
