Impulse Propagation and Pacemaking Flashcards Preview

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Flashcards in Impulse Propagation and Pacemaking Deck (17)
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decremental current flow

current flow and the resulting voltage changse that decreases with distance from the active area



proteins in gap junctions that contain the electrically conducting channels, varying in resistance


space constant (λ)

λ = sqrt(rm/ri)

the constant that describes the rate at which voltage declines from the injection site


time constant

the time it takes for V to decline by 1/e (~1/3)


safety margin for conduction

the likelihood of maintaining a regenerative wave of propagation

promoted by low internal resistance and high membrane resistance


M cells

midmyocardial cells in which the contribution of repolarizing K+ currents (especially the delayed rectifier) seems to be reduced

they consequently have a greater action potential duration than the endocardial or epicardial cells

also become disproportionately prolonged in response to factors that influence action potential duration such as cycle length, electrolyte concentration, and some drugs


What gives rise to the delay in the AV node?

a smaller margin of error due to the decreased voltage spike

this means that fewer cells are stimulated and the conduction speed is significantly decreased


velocity of conduction in the purkinje system

4 m/s


velocity of conduction in the atrium

1 m/s


velocity of conduction in the AV and SA nodes

0.5 m/s


Why is it useful to have a slow response AP in the AV node?

it gives the atria time to contract before the ventricles do


location of cells that can function as pacemakers

sinus node

atrial cells

AV nodal cells

purkinje fibers


funny current (If)

carried out by a non-selective cation channel that conducts both Na and K

activation is slow and it doesn't inactivate

slowly activates at the end of phase 3

Eq potential is around -20mV


What are the driving forces of phase 4 depolarization in the SA node?

membrane voltage clock

sarcolemmal calcium clock


membrane voltage clock

gradually increasing inward current If

gradually decreasing outward current IK

activation of T-type and L-type calcium channels in late phase 4


sarcolemmal calcium clock

works through the Na/Ca exchanger

rhythmic diastolic release of calcium by the sarcoplasmic reticulum via the ryanodine type 2 receptor activates the exchanger, which pumps out 1 Ca for an influx of 3 Na, thereby depolarizing the membrane


periphera SAN cells

serve to insulate the depolarized central cells, which are the dominant pacemakers

this prevents the well-polarized atrial myocardial cells from hyperpolarizing the central cells

done through differential characteristics of the connexins