SAN Action Potential Rate Explained

The sino-arterial node (SAN), located in the upper right atrium of the heart, acts as the natural cardiac pacemaker. It spontaneously generates electrical impulses, known as action potentials, which initiate the heartbeat.

Normal SAN Firing Rate

In a healthy adult human at rest, the intrinsic firing rate of the SAN typically ranges from 60 to 100 action potentials per minute. This rate determines the resting heart rate. However, factors like autonomic nervous system activity can modulate this rate.

Determining the Correct Option

The question asks for the number of action potentials generated by the SAN per minute in a healthy human. Based on physiological norms:

• Option 1: 70 - 75 bpm falls within the expected physiological range and represents a common resting heart rate.
• Option 2: 100 - 110 bpm is slightly high for a typical resting rate, approaching the upper limit or mild tachycardia.
• Option 3: 120 - 140 bpm indicates significant tachycardia.
• Option 4: 28 - 30 bpm is significantly below the normal range, suggesting bradycardia.

Therefore, the range of 70 - 75 action potentials per minute is the most appropriate answer representing the SAN's typical firing rate in a healthy individual.