Question

Assertion: SA node induces excitatory impulses in the heart.
Reason: S.A. node is self-excitatory.

• A. Both assertion and reason, are true and the reason is the correct explanation of assertion.
• B. Both assertion and reason, are true but the reason is not the correct explanation of the assertion.
• C. The assertion is true but the reason is false
• D. Both assertion and reason are false.

Answer 1

The correct option is A Both assertion and reason, are true and the reason is the correct explanation of assertion.

Sinu-auricular node or S-A node is located in the wall of the right auricle below the opening of superior vena cava. The S-A node has a unique property of self-excitation, which enables it to act as "pacemaker" of the heart. It spontaneously initiates a wave of contraction which spreads over both the auricles more or less simultaneously along the muscle fibres that fan out from the pacemaker.