Question

Heart beat originates from
A. Pacemaker
B. Cardiac muscles
C. Left atrium
D. Right ventricle

Answer 1

Hint: Heart beat is the rhythmic contraction and relaxation of the heart. One systole and one diastole is present in each heart beat to distribute and receive blood to and from the body. Our heart normally beats (average 72 beats min-1).

Complete answer:
The heart rhythm is maintained by a highly specialized excitatory and conductive system which includes sino-atrial node (SA node), intermodal pathways, the atrio-ventricular node (AV node), the AV bundle and the bundle of purkinje fibres.
Pacemaker – The sino-atrial node is also known as the natural pacemaker of the heart. It is a small, flattened and ellipsoid strip of muscle fibre of 0.3 mm size, which is situated in the upper lateral wall of the right atrium. It is responsible for initiation and maintaining the rhythmic contractile activity of the heart.
Cardiac muscles – These muscles are present in the walls of the heart. These muscles contract and relax which helps to circulate or pump the blood to all the body parts.
Left atrium – It helps to receive the oxygenated blood coming from the lungs by the help of pulmonary veins and pushes the blood into the left ventricle. It also changes its size during the cardiac cycle.
Left ventricle – It is located in the left portion of the heart. It is the thickest chamber of the heart and helps to pump the oxygenated blood to all the body parts or tissues.

So, the correct answer is option (A) Pacemaker, because it originates from the heart beats.

Note-
The heart beat is inversely proportional to age. In the foetus (140-150) per minute, in the newborn (130-140) per minute, in young (80-90) per minute, in adults (70-80) per minute, and below average (60 per minute) in old age. The smaller animals have higher metabolic rate, hence their heart rate is higher than larger animals.