Which of the following statements about conducting system of the heart is INCORRECT ?
I. Mass of nodal tissue seen in the lower-left corner of the right atrium is the sinoatrial node.
II. The nodal musculature can generate action potentials only in response to external stimuli .
III. The number of action potential that could be generated in a minute varies at different parts of the nodal system .
IV. The SAN can generate the maximum number of action potential , i.e., 80-85 `min^(-1)`

Options

A. I, II , III and IV
B. I, II and IV
C. II, III and IV
D. I,II and III

Answer

To determine which statements about the conducting system of the heart are incorrect, let's analyze each statement one by one:

### Step 1: Analyze Statement I
**Statement I**: "Mass of nodal tissue seen in the lower-left corner of the right atrium is the sinoatrial node."

- The sinoatrial node (SA node) is indeed located in the right atrium, but it is not in the lower-left corner; it is located in the upper wall of the right atrium. Therefore, this statement is **incorrect**.

### Step 2: Analyze Statement II
**Statement II**: "The nodal musculature can generate action potentials only in response to external stimuli."

- The nodal tissue, particularly the SA node, is auto-excitable, meaning it can generate action potentials without external stimuli. This statement is therefore **incorrect**.

### Step 3: Analyze Statement III
**Statement III**: "The number of action potentials that could be generated in a minute varies at different parts of the nodal system."

- This statement is true. Different parts of the nodal system (like the SA node and AV node) have different rates of action potential generation. Therefore, this statement is **correct**.

### Step 4: Analyze Statement IV
**Statement IV**: "The SAN can generate the maximum number of action potentials, i.e., 80-85 min^(-1)."

- While the SA node is the primary pacemaker, the average heart rate is typically around 72 beats per minute, with the SA node capable of generating up to 100 beats per minute under certain conditions. The stated range of 80-85 beats per minute is somewhat misleading as it does not represent the average. Therefore, this statement is also **incorrect**.

### Conclusion
Based on the analysis:
- **Incorrect Statements**: I, II, and IV
- **Correct Statement**: III

Thus, the answer is that statements I, II, and IV are incorrect.

### Final Answer
**The incorrect statements about the conducting system of the heart are I, II, and IV.**

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