Question

Assertion: The muscle fibres of SA nodes possess the lowest rhythmicity among all cardiac muscle fibres.
Reason:Due to this fact it can initiate exciton waves at the highest rate
A.If both the assertion and the reason are true and the reason are true and the reason is a correct explanation of the assertion
B.If both the assertion and the reason are true but the reason are true and the reason is not a correct explanation of the assertion
C.If both the assertion is true but the reason is false
D.If both the assertion and reason are false

Answer 1

Hint: The SA node is the heart's natural pacemaker. The SA node comprises a cluster of cells that are situated in the upper part of the wall of the right atrium (the right upper chamber of the heart). The electrical impulses are produced there.

Complete answer:
SA which is sinoatrial node and AV which is atrioventricular node are contraction nodes in the mammalian heart. SA node muscle fibers have the top level rhythmicity among all cardiac muscle fibers because of which they can produce excitatory waves at the highest rate. Therefore, cardiac impulses normally originate from SA nodes.
 Thus, the correct answer is option D.

Note: The sinoatrial hub, additionally alluded to as the pacemaker of the heart, facilitates heart withdrawals. Situated in the upper mass of the correct chamber, it creates nerve driving forces that move all through the heart divider making the two atria contract. The SA hub is managed by the autonomic nerves of the fringe sensory system.