Question

How does the sinoatrial node (SA node) primarily initiate the depolarizing impulse in the heart?

A) By increasing efflux of potassium (K+)
B) By decreasing efflux of potassium (K+) and increasing influx of sodium (Na+)
C) By increasing efflux of sodium (Na+)
D) By maintaining the normal balance of potassium (K+) and sodium (Na+) influx

Answer 1

The sinoatrial node initiates heart depolarization by decreasing potassium efflux and increasing sodium influx until an action potential is triggered, resulting in heart contraction.

Step-by-step explanation:

The sinoatrial node (SA node) primarily initiates the depolarizing impulse in the heart by decreasing the efflux of potassium (K+) and increasing the influx of sodium (Na+), which leads to the generation of an action potential. During the pacemaker potential phase, the automaticity of the SA node cells allows for a gradual depolarization, primarily due to a slow inflow of Na+ and a decrease in K+ permeability. Once the threshold is reached, a rapid depolarization phase occurs mainly due to the opening of voltage-gated calcium channels. Therefore, the correct answer to the student's question is B) By decreasing efflux of potassium (K+) and increasing influx of sodium (Na+).