Cardiac action potential

Question 1

How many phases does the cardiac action potential have?

Answer 1

There are five phases of the cardiac action potential, from phase 0 to phase 4.

Depolarization is the result of the net inward movement of positively charged ions.

Repolarization occurs from net outward movement of positively charged ions.

The ion fluxes are different in non-pacemaker and pacemaker cells but the overall ion movement is the same.

Question 2

Automaticity results from depolarization during which phase?

Answer 2

Automaticity results from depolarization during Phase 4 secondary to an inward Na+ current.
This slow depolarization can be enhanced by a number of factors e.g. adrenergic stimulation. Examples include; inappropriate sinus tachycardia and atrial tachycardia.

Question 3

Answer 3