Car 10 - Electrophysiology

Question 1

What is an action potential?

Answer 1

Electrical membrane potential of cell rapidly rises and falls.

Question 2

What would be the optimal range of mV for ventricular action potential for K+ only?

Answer 2

-75 to -95 mV.

Question 3

What would be the optimal range of mV for ventricular action potential for Na+ only?

Answer 3

+50 mV.

Question 4

What would be the optimal range of mV for ventricular action potential for Ca2+ only?

Answer 4

+20 mV.

Question 5

What is happening in phase 0 of myocardial action potential?

Answer 5

The voltage-gated Na channel opens, increasing Na permeability, depolarizing from initial -90 mV to all the to around +20 mV.

Question 6

What is happening in phase 1 of myocardial action potential?

Answer 6

The initial repolarization; inactivation of the Na channels and therefore the action potential is going down and the opening of K+ channels is going to make go back down as well.

Question 7

What is happening in phase 2 of myocardial action potential?

Answer 7

AKA the plateau phase. Phase 2: myocyte contraction: voltage-gated Ca2+ channels opening, raising the depolarization back to +20 mV again. The influx of Ca2+ is what triggers the myocyte contraction.

Question 8

What is happening in phase 3 of myocardial action potential?

Answer 8

Rapid repolarization: more K+ channels open and the Ca2+ closes.

Question 9

What is happening in phase 4 of myocardial action potential?

Answer 9

Back at -90 mV thanks to influx of K+. The K+ have now closed.

Question 10

What is the effective refractory period (ERP)?

Answer 10

It is b/w phase 0 to end of phase 3 of ventricular action potential; you cannot elicit another phase 0 depolarization. Antiarrhythmics increase this period.

Question 11

What is the difference b/w pacemaker action potential vs ventricular action potential?

Answer 11

Pacemaker action potential does not have a phase 1 or 2. In phase 0, Ca2+ depolarizes the cell in pacemakers instead of Na+ like in the ventricles. No plateau in pacemaker cells.

Question 12

What is happening in phase 4 of pacemaker action potential?

Answer 12

Na+ channels are slowly opening that depolarize the cell from -70 mV to -40 mV; it does not rest, it is always increasing.

Question 13

What is happening in phase 0 of pacemaker action potential?

Answer 13

Ca2+ channels open, depolarizing the cell from -40 to 10 to 20 mV.

Question 14

What is happening in phase 3 of pacemaker action potential?

Answer 14

Inactivation of Ca2+ channels. K+ channels open to repolarize the cell back to -70 mV (the resting potential).

Question 15

What physiology accounts for the automaticity of the AV and SA nodes?

Answer 15

Phase 4 gradual Na+ conductance.