Question

Rate of the heartbeat is determined by:
(a) Purkinje Fibres
(b) Papillary Muscle
(c) AV Node
(d) SA Node

Answer 1

The part of the heart that is involved in determining the rate of heartbeat consists of a cluster of cells and lies in the upper part of the wall of the right atrium.

Complete answer:
The heart is a muscular blood pumping organ consisting of cardiac muscles and its pumping action is regulated by an electrically conducting system which is formed of a network of muscle fibres. The electrical impulses are generated by the cluster of cells lying in the right wall of the right atrium and are known as the SA(sino-atrial) node which determines the rate of heartbeat.

SA nodes contain myocytes (muscle cells) which are capable of spontaneous generation of electrical impulse. This impulse is then transmitted to the right atrium and then through the whole conduction system of the heart which results in myocardial contraction leading to blood distributed to the rest of the body. This sinus node continuously generates the electrical impulse and thus sets the normal rhythm and rate of the heart.
SA node is also known as a natural pacemaker of the heart for its function and in fact, if this sinus node doesn't work properly an artificial pacemaker is introduced in the body for impulse generation.
So, the correct answer is, “SA node”.

Note:
-When the SA node doesn’t work properly, this condition is known as “sick sinus syndrome”.
-An ECG (Electrocardiogram) is a device for recording the electrical signal of the heart and report improper functioning of heart if any.