CPR Cardiac Action Potentials & Conduction Flashcards Preview

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Flashcards in CPR Cardiac Action Potentials & Conduction Deck (26)
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Describe how an action potential spreads in heart

SA node
AV node
Bundle of His
R/L bundle branches
Purkinje fibers


What maintains the order of stimulus in the heart?

overdrive suppression of the SA node


Why is the SA node in "control" of pacemaking properties?

the SA node generates action potentials most frequently (followed by AV node & then the Purkinje fibers)


Where is the delay in the action potential?

@ the AV node


Which cells have the highest velocity?

Purkinje cells because have the largest diameter


Describe the order of contraction of the heart

RA contracts before LA

endocardium contracts before epicardium

RV epicardium contracts before LV epicardium


What is unique about the SA node membrane potential?

resting Vm is more positive compared to resting Vm of ventricles & atria


What is phase 4 assoc w/ in the SA node?

open of funny Na channels to cause rise in membrane potential in SA node


What is responsible for phase 2?

combo of inward Ca2+ current, outward K+ current & inward rectifiers (K1)

inward Ca2+ current via L-type Ca2+ channels


What is responsible for phase 1?

transient outward K+ current via K+ channels


What is responsible for transition from phase 2 to phase 3?

voltage gated K+ channels (outward K+ current!)


Does the AP or contraction occur first?

the AP occurs before the contraction


What channels are always open?

K+ leak channels are open all the time

would have increased current outward during phase 2


What provides the rhythmicity of contractions?

SA & AV nodes are primary source


What occurs in phase 4 in SA & AV nodes?

resting Vm gradually depolarizes until reaches threshold & then fires (more slowly in AV node)

due to funny voltage-gated Na+ channels that open upon COMPLETE repolarization of membrane


What occurs in phase 0 in SA node?

opening of voltage gated Ca+ channels (not Na+ channels) & closure of voltage gated K+ channels


What occurs in phase 3 in SA node?

reversal of phase 0 w/ closure of voltage gated Ca+ channels & opening of voltage gated K+ channels


How are the SA & AV nodes controllers of the contracting rhythm of heart?

will naturally depolarize to reach threshold w/o electrical stimulation

stimulation of AV node by SA node will trigger AV node to generate AP before it can make its own


Why are refractory periods longer in cardiac cells?

help to prevent arrhythmias


What is the supranormal period?

cell is more excitable than normal & easier to generate AP (may have abnormal conduction)


How does an AP compare if stimulated in RRP or SNP?

conduction of AP will be weaker


Describe parasympathetic innervation of heart

carried by vagus N to SA & AV nodes

ACh binds to muscarinic receptor (M2/M3)


Parasympathetic effects on AP

negative chronotropic (slower opening of funny Na+ & hyperpolarization of SA node by increasing K+ outflow via special K+ channels)

negative dromotropic (reduced Ca+ inward current & hypopolarizes SA node b/c decreases outward + current)


Describe sympathetic innervation of heart

to SA node, AV node & ventricular myocytes

Norepi binds to B1 adrenergic receptor


Sympathetic effects on AP

positive chronotropic effects (more rapid opening of Na+ channels & hypopolarizes SA node)

positive dromotropic effects (increased inward Ca2+ current & hyperpolarization of SA node)

positive inotropic influence


Sympathetic v Parasympathetic on HR

Sympathetic: hypopolarize & increase inward Na+

Parasympathetic: hyperpolarize & decrease inward Na+