Question

Which effect do epinephrine and norepinephrine primarily have on the SA node?

A) Decrease ion flow through sodium channels
B) Increase ion flow through sodium channels
C) Increase ion flow through potassium channels
D) Have no effect on ion channels

Answer 1

Epinephrine and norepinephrine bind to beta-1 receptors in the SA node, increasing ion flow through sodium channels and leading to faster depolarization and a shortened repolarization period.

Step-by-step explanation:

The hormones epinephrine and norepinephrine have a significant effect on the SA (sinoatrial) node of the heart. They both bind to the beta-1 receptors on the SA node, leading to the opening of sodium and calcium ion channels. The effect of these catecholamines is to increase the ion flow through sodium channels, which in turn increases the rate of depolarization. Because of this, the threshold for depolarization is reached more quickly, and the period of repolarization is shortened. Therefore, the correct answer to which effect epinephrine and norepinephrine primarily have on the SA node is B) Increase ion flow through sodium channels.