All the components of the nodal tissue are autoexcitable. Why does the SA node act as the normal pacemaker?

(A)SA node has the highest rate of depolarisation.
(B)SA node has the lowest rate of depolarisation.
(C)SA node is the only component to generate the threshold potential.
(D)Only SA node can convey the action potential to the other components.

The NCERT line that answers it

Verbatim line

The SAN can generate the maximum number of action potentials, i.e., $70-75 \text{ min}^{-1}$ , and is responsible for initiating and maintaining the rhythmic contractile activity of the heart.

Chapter: Body Fluids and Circulation
Section: 15.3.1 Human Circulatory System

The answer appears as a continuous sentence in NCERT. This is that sentence.

How this line gives the answer

0, emb=1.0, combined=1.0). Verified: high — The span explicitly states that the SAN 'can generate the maximum number of action potentials, i.e., 70-75 min⁻¹', which directly corresponds to 'the highest rate of depolarisation' (option A), distinguishing it from other nodal components.

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