Question

The number of action potentials generated by sino-atrial node (SAN) in a healthy human is ______ per minute.

• A. 120 – 140
• B. 28 – 30
• C. 70 – 75
• D. 100 – 110

Hint:

SAN = Natural pacemaker of heart. Normal firing rate = 70–75 impulses per minute. This controls normal resting heart rhythm.

Answer 1

The Correct Option is C

Concept: The sinoatrial node (SAN) is called the natural pacemaker of the human heart. It is a specialized group of cardiac muscle fibers located in the right atrium. Its main function is to generate electrical impulses automatically. These electrical impulses initiate each heartbeat. The rate at which SAN generates impulses determines the normal heart rate. In healthy adults, SAN generates approximately 70 to 75 electrical impulses every minute.

Step 1: Understand the role of sinoatrial node.
The human heart contains specialized tissues responsible for generating rhythmic impulses. The sinoatrial node is the primary pacemaker. Its impulse spreads through atria causing atrial contraction. Because SAN starts every heartbeat, its firing rate determines heartbeat frequency.

Step 2: Recall normal physiological rate.
According to human physiology, SAN generates approximately \[ 70-75 \] action potentials every minute. Each impulse initiates one heartbeat. Therefore resting heart rate remains approximately within this range.

Step 3: Examine wrong options.
120–140 → much higher than normal resting rate 28–30 → abnormally low 100–110 → higher than normal physiological average 70–75 → correct physiological range

Step 4: Final conclusion.
Thus normal impulse generation rate of SAN is \[ 70-75 \] Hence correct answer is \[ \boxed{\text{Option (3)}} \]