Leblanc Flashcards
Hypokalemia (accelerates/depresses) automaticity
accelerates
Hyperkalemia (accelerates/depresses) automaticity
depresses
Hyperkalemia leads to a (blank) in upstroke and conduction velocity.
decrease
How is conduction velocity related to cell diameter?
It is directly proportional. Think of the AV node: small cells, so the conduction velocity is SLOW.
Conduction velocity is also enhanced by the (blank) of the action potential which allows for activation of more distal downstream cells and their subsequent activation (domino effect)
height
How is conduction velocity related to the resting membrane potential?
Conduction velocity is inversely proportional to the resting potential. Membrane depolarization reduces the availability of Na+ channels. This decreases the rate of rise of Phase 0 in non-pacemaker cells.
Slow response action potentials in ventricular cells
are similar to the action potentials in what kind of cells?
SA nodal cells
What ionic current is responsible for the following phases in SA node cells:
Phase 0
Phase 3
Phase 4
Phase 0: Ca+ current
Phase 3: Ca+ current, K+ current
Phase 4: K+ current, Ifunny (pacemaker current)
Non-pacemaker cells (atrial, ventricular, Purkinje cells) exhibit a (blank) permeability ratio of Na:K (~ 1-3:100) and are thus more (blank) (more negative RP) than pacemaker cells (SA and AV node) which display a relatively (blank) permeability ratio of Na:K (~ 1:5-10)
low
polarized
high
So, which type of cell, pacemaker or non-pacemaker cells, has a greater permeability to Na, or a smaller Na:K ratio?
SA nodal cells have many more Na+ channels available
What is the resting membrane potential of SA nodal cells?
-55 to -65 mV
What is the resting membrane potential of ventricular cells?
-80 to -85 mV
Purkinje cells are (small/large), so there is (slower/faster) propagation of the signal.
Large; faster
Purkinje cells have tons of (blank), which explains their quick action potential. SA nodal cells have fewer (blank), so a slower conduction.
gap junctions
Speed of conduction through the AV node is not primarily dependent on the refractory period. It is more so dependent on what?
The height of the action potential, and thus the effect downstream.
What is another way to think of depolarization?
Decreased availability of Na+ channels
Refractory period is a measure of (blank).
Excitability
In lead 1, which arm is positive?
left arm is positive
In lead 2, left leg is positive. Which arm is negative?
right arm is negative
In lead 3, left leg is positive. Which arm is negative?
left arm is negative
The (blank) depolarizes first and repolarizes last.
Endocardium
In aVr, how are the electrodes placed?
Positive electrode on the right arm.
Negative electrodes on left arm and left foot.
In aVL, how are the electrodes placed?
Positive electrode on the left arm.
Negative electrodes on right arm and left foot.
In aVf, how are the electrodes placed?
Positive electrode on left foot. Negative electrodes on both arms.
Does current travel toward positive or negative electrode?
Positive!
Difference between EADs and DADs. One similarity between the two.
EADs: reopening of Ca2+ channels
DADs: intracellular Ca2+ overload. The presence of high intracellular Ca2+ causes a premature action potential resulting in an extra ventricular systole.
Both can be caused by low K+ channel activity
