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NEET2011ZoologyBody Fluids and CirculationActual

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

Options

  1. AIf both assertion and reason are true and reason is the correct explanation of assertion
  2. BIf both assertion and reason are true but reason is not the correct explanation of assertion
  3. CIf assertion is true but reason is false
  4. DIf both assertion and reason are false.

Correct answer

B. If both assertion and reason are true but reason is not the correct explanation of assertion

Step-by-step solution

Sinu-auricular node or S-A node is located in the wall of the right auricle below the opening of the superior vena cava. The S-A node has unique property of self excitation, which enables it to act the "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.

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