NEET 2019 · BiologyPrevious Year Question
All the components of the nodal tissue are autoexcitable. Why does the SA node act as the normal pacemakar?
Answer: (D) SA node has the highest rate of depolarisation.. Answer: (d) SA node has the highest rate of depolarisation.
- A.SA node has the lowest rate of depolarisation.
- B.SA node is the only component to generate the threshold potential.
- C.Only SA node can convey the action potential to the other components.
- D.SA node has the highest rate of depolarisation.✓
Correct Answer
(D) SA node has the highest rate of depolarisation.
Solution & Explanation
Answer: (d) SA node has the highest rate of depolarisation. Solution: Although all nodal tissue is autoexcitable, the SA node can generate the maximum number of action potentials per minute (70-75/min). Because it depolarises fastest, it sets the pace and is called the pacemaker; the other components are entrained to its rhythm. NCERT: Ch 15, p.199, line 23 — "The SAN can generate the maximum number of action potentials"
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