Question

The heart of a healthy man normally beats ________ per minute.
A. 60-70 times
B. 70-80 times
C. 80-90 times
D. 85-95 times

Answer 1

Hint: The entire heart is made of cardiac muscles. Nodal tissue is a specialized cardiac musculature that is also distributed in the heart. Sino-atrial node (SAN) is a patch of this tissue, present in the right atrium at its upper right corner. Atrioventricular node (AVN), another mass of this tissue is present close to the atrioventricular septum in the lower-left corner of the right atrium.

Complete answer:
- A bundle of nodal fibers present called atrioventricular bundle (AV bundle) emerges from the AVN, goes through the atrioventricular septa and then comes out on the top of the interventricular septum. It is then further divided into a right and left bundle.
- The nodal musculature is auto-excitable and can generate action potentials without any external stimuli.
- Action potential is a short-term phenomenon in which the electrical membrane potential rapidly rises and falls in a cell. Although all the heart muscle cells have the ability to generate the electrical impulses that trigger cardiac contraction, the SAN initiates it, simply because it generates the maximum number of action potentials that is 70-75 per minute.
- The rhythmic contractile ability of the heart is maintained by the sino-atrial node. Due to this property, it is referred to as the pacemaker of the heart.
- Our heart usually beats 70-75 times in a minute. This is called the heart rate.

Hence, the correct answer is option (B).

Note: - The sino-atrial node is also referred to as the natural pacemaker of the heart. When it does not work properly, an artificial pacemaker is implanted so that the normal heartbeat can be restored and maintained.
-The concept of artificial pacemaker was introduced by Chardack in 1960.