Cardiac Ion Channels & AP Flashcards Preview

CV wk1 and wk2 > Cardiac Ion Channels & AP > Flashcards

Flashcards in Cardiac Ion Channels & AP Deck (25):
1

Electrical signal originates in ____ and propagates through ___ and ___

originates in myocardium propagates through atria and specialized conduction pathways

2

HR is controlled by which cells located where?

pacemaker cells in SA node

3

Intrinsic firing rate of SA nodal cells? Modulated by what?

100/min; modulated by ANS

4

What effect does the parasympathetic tone have on firing rate?

Depresses it to 60-80/min

5

What is overdrive suppression

SA nodal cell pacemaking is faster than other regions. As a result, it drives and dominates over the other regions (overdriven by SA node)

6

Ectopic pacemakers

Cells outside of the SA node that can take on initiation of heartbeat under abnormal circumstances (ie damage, hypoxia)

7

Where does cell-to-cell propagation occur?

Via gap junctions - direction of propagation is controlled by junction position and by the CT that "insulates"

8

Where can APs propagate from SA node to the ventricles?

at the AV node

9

Slow AP occurs where?

SA node and AV node

10

Fast AP occurs where?

Atrial muscle
Ventricular muscle
Purkinje fiber
Bundle of His
L & R bundle branches

11

Vm < Eion current flows _____ cell; causes _____

Vm > Eion current flows _____ cell; causes _____

Vm < Eion flows into cell causing depolarization

Vm > Eion flows out of cell causing hyperpolarization

12

What is unique about If (or Ih) channels?

Opposite from the other channels in that it is activated by hyperpolarization. Allows cation fluxes and can lead to reversal potential. Can help generate rhythm.

13

Fast cardiac AP include what channels?
- list the current that they represent

INa
ICa-L

IKto (transient outward current)
IKr + IKs
IK1

14

Slow cardiac APs include what channels?

ICa-T + ICa-L
If
IKr + IKs

15

What is the delayed rectifier current?
What is the inward rectifier channels?

Delayed recifier: IKr + IKs

Inward rectifier: IK1

16

Funny current

funny channel, or If, or IKf, or pacemaker current) refers to a mixed sodium-potassium current in the heart that activates upon hyperpolarization

17

Fast AP:
- Phase 0

○ Initial upstroke, rapid depolarization
- caused by entry of INa through voltage activated sodium channels.

18

Fast AP:
- Phase 1

○ Small, partial repolarization
- because of inactivation of INa and activation of transient IKto

19

Fast AP
- Phase 3

Termination of plateau by rapid repolarization back to ~-90mV
○ Continued outward Potassium current (IKr+Iks)
○ Low membrane permeability for other cations
○ Inactivation of Na and Ca are removed

20

Fast AP
- Phase 4

○ Cell is held near EK by the inward rectifier channel (IK1)
○ Negative voltage/resting potential

21

Slow AP
- Phase 0

○ Upstroke from activation(opening) of ICa-T and ICa-L
○ Slow because no INa

22

Slow AP
- Phase 1

Does not exist in slow APs

23

Slow AP
- Phase 2

Does not exist in slow APs

24

Slow AP
- Phase 3

Rapid repolarization
○ Occurs shortly after peak of AP because of ICa-T and ICa-L channels close and K channels open (effluxes)

-Membrane potential goes towards K( ~-60)

(Na is still entering the cell at very low amts)

25

Slow AP
- Phase 4

"the peacemaker potential"
initiated by Funny current
- (or funny channel, or If, or IKf, or pacemaker current)- mixed sodium-potassium current that activates upon hyperpolarization and supplies inward current

Na+ slowly leaks into the cell
(peak slightly rises until phase 0 initiated)
○ Brings cell back to threshold for generation of another AP