OME Cardiac Modules Practice Test

Phase 0 of the SA node action potential occurs due to entry of which ion?

Calcium enters Sodium enters Potassium leaves Chloride enters

Correct Answer:

Calcium enters

Explanation:

Phase 0 in the SA node is driven by calcium entry through L-type calcium channels. Pacemaker cells rely on Ca2+ for the rapid depolarization because they lack the fast Na+ current that drives phase 0 in ventricular tissue. The Ca2+ influx raises the membrane potential to initiate the upstroke. Sodium entering would mainly depolarize in non-pacemaker heart tissue, potassium leaving would hyperpolarize/repolarize, and chloride influx isn’t responsible for this rapid depolarization.

Access more questions from this quiz

Continue to OME Cardiac Modules Practice Test for more practice questions and the full quiz experience.

Access More Questions