Leblanc

Question 1

Hypokalemia (accelerates/depresses) automaticity

Answer 1

accelerates

Question 2

Hyperkalemia (accelerates/depresses) automaticity

Answer 2

depresses

Question 3

Hyperkalemia leads to a (blank) in upstroke and conduction velocity.

Answer 3

decrease

Question 4

How is conduction velocity related to cell diameter?

Answer 4

It is directly proportional. Think of the AV node: small cells, so the conduction velocity is SLOW.

Question 5

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)

Answer 5

height

Question 6

How is conduction velocity related to the resting membrane potential?

Answer 6

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.

Question 7

Slow response action potentials in ventricular cells

are similar to the action potentials in what kind of cells?

Answer 7

SA nodal cells

Question 8

What ionic current is responsible for the following phases in SA node cells:
Phase 0
Phase 3
Phase 4

Answer 8

Phase 0: Ca+ current
Phase 3: Ca+ current, K+ current
Phase 4: K+ current, Ifunny (pacemaker current)

Question 9

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)

Answer 9

low
polarized
high

Question 10

So, which type of cell, pacemaker or non-pacemaker cells, has a greater permeability to Na, or a smaller Na:K ratio?

Answer 10

SA nodal cells have many more Na+ channels available

Question 11

What is the resting membrane potential of SA nodal cells?

Answer 11

-55 to -65 mV

Question 12

What is the resting membrane potential of ventricular cells?

Answer 12

-80 to -85 mV

Question 13

Purkinje cells are (small/large), so there is (slower/faster) propagation of the signal.

Answer 13

Large; faster

Question 14

Purkinje cells have tons of (blank), which explains their quick action potential. SA nodal cells have fewer (blank), so a slower conduction.

Answer 14

gap junctions

Question 15

Speed of conduction through the AV node is not primarily dependent on the refractory period. It is more so dependent on what?

Answer 15

The height of the action potential, and thus the effect downstream.

Question 16

What is another way to think of depolarization?

Answer 16

Decreased availability of Na+ channels

Question 17

Refractory period is a measure of (blank).

Answer 17

Excitability

Question 18

In lead 1, which arm is positive?

Answer 18

left arm is positive

Question 19

In lead 2, left leg is positive. Which arm is negative?

Answer 19

right arm is negative

Question 20

In lead 3, left leg is positive. Which arm is negative?

Answer 20

left arm is negative

Question 21

The (blank) depolarizes first and repolarizes last.

Answer 21

Endocardium

Question 22

In aVr, how are the electrodes placed?

Answer 22

Positive electrode on the right arm.

Negative electrodes on left arm and left foot.

Question 23

In aVL, how are the electrodes placed?

Answer 23

Positive electrode on the left arm.

Negative electrodes on right arm and left foot.

Question 24

In aVf, how are the electrodes placed?

Answer 24

Positive electrode on left foot. Negative electrodes on both arms.

Question 25

Does current travel toward positive or negative electrode?

Answer 25

Positive!

Question 26

Difference between EADs and DADs. One similarity between the two.

Answer 26

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