University of Central Florida (UCF) ZOO3733C Human Anatomy Practice Exam 3

The sinoatrial (SA) node is known as the natural pacemaker of the heart. It generates electrical impulses that initiate the heart's rhythm. The normal spontaneous firing rate of the SA node typically ranges from about 60 to 100 impulses per minute in a resting adult.

The choice of approximately 70 impulses per minute reflects an average rate within that normal range. This is significant because the SA node regulates heart rate and maintains a regular rhythm by automatically generating impulses that stimulate the atria to contract, which is crucial for proper cardiac function.

In summary, the selection of approximately 70 impulses per minute is accurate because it represents a typical, healthy rate of spontaneous activity from the SA node that maintains a steady heart rhythm.