Question

In human beings heartbeat is initiated by
(a) Purkinje fibers
(b) AV node
(c) SA node
(d) Bundles

Answer 1

Hint: This is a small mass of specialized cells lying in the wall of the right atrium near the opening of the superior vena cava. It is referred to as the natural pacemaker of the heart.

Complete answer:
In human beings, the heartbeat is initiated by the SA node (sinoatrial node) because they are electrically unstable. It is also known as the heart’s natural pacemaker. The impulse starts during a small bundle of specialized cells located within the right atrium of the heart, called the SA node. The electrical activity spreads across the walls of the atria and causes them to contract. This forces blood into the ventricles. The sinoatrial node sets the speed and rhythm of your heartbeat. Normal cardiac rhythm is usually called normal sinus rhythm because the SA (sinus) node fires regularly.

AV node (atrioventricular node) : The AV node is a cluster of cells in the center of the heart between the atria and ventricles, and acts like a gate that slows the electrical signal before it enters the ventricles. This interval gives the atria time to contract before the ventricles do.
Atrioventricular bundle (AV bundle or bundle of his) : This is the mass of specialized fibers that originate from the AV node. The AV bundle crosses the fibrous ring that divides atria and ventricles. They transmit the impulse to the muscular walls of the ventricles and cause them to contract and by this, the blood comes out of the heart and goes to the lungs and body.
Purkinje fibers: They are located in the inner ventricular walls of the heart, just beneath the endocardium in a space. The Purkinje fibers are specialized conducting fibers composed of electrically excitable cells and conduct cardiac action potentials more quickly and efficiently than any other cells in the heart.

So, the correct answer is ‘SA node’.


Note: At rest, the SA node causes your heart to beat about 60 to 100 times each minute. During activity or excitement, our body needs more oxygen-rich blood, the heart rate rises to well over 100 beats per minute.