Question

Explain the process of origin of heart beat.

Answer 1

Hint: The heart works by an electric system, where the ventricle and the atria alternately contract and relax to pump blood. The SA node is the natural cardiac pacemaker. The AV node is the pathway through which the impulses pass.

Complete step by step answer: The SA nodes are the small bundle of cells located at the right atrium. The impulse starts from these nodes and the electrical activity spreads in the walls of the atria causing it to contract. The contraction thus taking place forces the blood to the ventricles and thus the rate and rhythm of the heartbeat are set. The cluster of the cells in the centre of the heart is the AV node. This lies between the atria and the ventricle. The AV node slows down the electrical signal by acting as a gate before the signal enters the ventricles. The delay thus caused, gives time to the atria to contract before the ventricles do.
The pathway of fibres which sends the impulse to the muscular walls is called His-Purkinje Network. This helps in the contraction of the ventricles and thus forces the blood out from the heart to the lungs.
It is clear from the above explanation, that the Sino-Atrial node can control the rate of the entire heartbeat.

Note: In a normal heart, there are fifty to ninety-nine beats per minute during rest. In the case of fever and some other diseases, the heartbeat can become faster than normal. The contraction and relaxation of the heart system do not involve the brain.