Assertion: Muscle fibres of SA node possess the lowest rhythmicity among all cardiac muscles.
Reason: Due to this fact, it can initiate excitatory waves at the highest rate.
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.
(e) If the Assertion is incorrect but the Reason is correct.
(e) If the Assertion is incorrect but the Reason is correct.
Explanation:
The sinoatrial or sinoauricular node determines the rate of heart beat by determining the rate of discharge of cardiac impulse. It is called the pace maker. It is formed of specialized cardiac muscles and is located in the right atrial wall near the opening of superior venacava. These muscles are self excitable. Since it is self excitable, it can produce waves at highest rate. Hence, the assertion is incorrect.