Directions for: The questions consist of two statements each, printed as assertion and reason. While answering these questions you are required to choose any one of the following five responses A. If both the Assertion 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 is not a correct explanation of Assertion. C. If the Assertion is true but the Reason is false. D. If both the Assertion and the Reason are false. E. If Assertion is false but Reason is true.
Assertion: Muscles fibres of SA node possess the lowest rhythmicity among all cardiac muscles Reason: Due to this fact, it can initiateexcitory wave at the highest rate.A) A
B) B
C) C
D) D
E) E
Correct Answer: E
Solution :
SA (Sino atrial) node and AV (Atrio ventricular) nodes are contraction nodes in mammalian heart. SA node muscle fibers have highest rhythmicity among all cardiac muscles fibers and can initiate excitatory wave at highest rate. Therefore, cardiac impulses normally originates from SA node.
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