Assertion `:` The sino-atrial node (SAN) is called the pacemaker.
Reason `:` SAN is responsible for initiating and maintaining the rhythmic contractile activity of the heart.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion .
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are false.

Answer

**Step-by-Step Solution:**

1. **Understanding the Assertion**: The assertion states that the sino-atrial node (SAN) is referred to as the pacemaker of the heart. This is a widely accepted fact in human physiology.

2. **Understanding the Reason**: The reason provided states that the SAN is responsible for initiating and maintaining the rhythmic contractile activity of the heart. This means that the SAN generates electrical impulses that trigger heartbeats.

3. **Location of the SAN**: The sino-atrial node is located in the upper portion of the right atrium of the heart. It is made up of specialized nodal tissue that has the ability to generate electrical signals.

4. **Function of the SAN**: The SAN generates electrical impulses that spread throughout the heart muscle, causing it to contract in a coordinated manner. This rhythmic contraction is essential for effective pumping of blood.

5. **Conclusion**: Since both the assertion and reason are correct, and the reason correctly explains why the SAN is called the pacemaker, we can conclude that both statements are true and that the reason is the correct explanation for the assertion.

**Final Answer**: Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.

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