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

Step 1: Identify the structure.
The sino-atrial node (SAN) is the natural pacemaker of the heart, sitting in the right atrium.
Step 2: Know its job.
It fires electrical impulses on its own, and each impulse starts one heartbeat.
Step 3: Link firing rate to heart rate.
Since SAN starts every beat, its firing rate sets the resting heart rate.
Step 4: Recall the normal value.
In a healthy adult the SAN fires about 70 to 75 times per minute.
Step 5: Reject the wrong ranges.
120 to 140 and 100 to 110 are too high, and 28 to 30 is far too low.
Step 6: Conclude.
The correct range is 70 to 75 per minute, which is option 3.
\[ \boxed{70\ \text{to}\ 75} \]