Assertion: The nodal musculature has the ability to generate action potentials without any external stimuli, i.e., it is auto-excitable.
Reason: The number of action potentials that could be generated in a minute very at different parts of the nodal system.

Options

A. If both asseration and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true reason is false.
D. If both assertion and reason are false.

Explanation

To solve the question regarding the assertion and reason statements about nodal musculature, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understand the Assertion**:
- The assertion states that the nodal musculature can generate action potentials without external stimuli, indicating that it is auto-excitable.
- This is true because the nodal tissues, such as the sinoatrial (SA) node in the heart, have specialized cells that can spontaneously depolarize and initiate action potentials.

**Hint**: Think about the role of the SA node in the heart and its ability to initiate heartbeats.

2. **Evaluate the Reason**:
- The reason states that the number of action potentials generated in a minute varies at different parts of the nodal system.
- This is also true. Different parts of the nodal system (like the SA node, atrioventricular (AV) node, and Purkinje fibers) have different rates of spontaneous depolarization, leading to variations in the frequency of action potentials.

**Hint**: Consider how the SA node typically fires faster than the AV node and how this affects heart rhythm.

3. **Determine the Relationship**:
- While both statements are true, the reason does not provide a correct explanation for the assertion. The assertion is about the auto-excitability of nodal musculature, while the reason discusses the variability in action potential frequency, which does not explain why the nodal musculature is auto-excitable.

**Hint**: Reflect on whether the reason logically explains the assertion or if it merely states a related fact.

4. **Conclusion**:
- Since both the assertion and reason are true, but the reason does not correctly explain the assertion, the correct answer is that both statements are true, but the reason is not the correct explanation of the assertion.

**Hint**: Look for options that match this conclusion regarding the truth of both statements and the nature of their relationship.

### Final Answer:
The correct answer is that both the assertion and reason are true, but the reason is not the correct explanation of the assertion.