'X'' is a fibrous tissue of the membranous septum of the heart just above the septal cusp of the tricuspid valve. It separates the atrium and the ventricle of the same side. Identify "X" ?

Options

A. Sinoatrial node
B. Atrioventricular septum
C. Atrioventricular node
D. Interventricular septum

Answer

To identify the fibrous tissue "X" of the membranous septum of the heart that is located just above the septal cusp of the tricuspid valve and separates the atrium and ventricle of the same side, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of the Heart**: The heart consists of four chambers: two atria (right and left) and two ventricles (right and left). The right atrium is connected to the right ventricle through the tricuspid valve, while the left atrium connects to the left ventricle via the mitral valve.

2. **Identify the Location of "X"**: The question specifies that "X" is a fibrous tissue located in the membranous septum of the heart, just above the septal cusp of the tricuspid valve. This indicates that "X" is situated between the right atrium and right ventricle.

3. **Differentiate Between Various Structures**:
- The **sinoatrial (SA) node** is a pacemaker located in the right atrium but is not a fibrous tissue.
- The **atrioventricular (AV) node** is also a node that transmits signals between the atria and ventricles, but it is not a septum.
- The **interventricular septum** is the wall separating the left and right ventricles, not the atria and ventricles.

4. **Identify the Correct Structure**: The structure that separates the atrium and ventricle on the same side (right side in this case) and is a fibrous tissue is the **atrioventricular septum**. This septum is specifically located just above the septal cusp of the tricuspid valve.

5. **Conclusion**: Therefore, the fibrous tissue "X" that separates the atrium and ventricle of the same side and is located just above the septal cusp of the tricuspid valve is the **atrioventricular septum**.

### Final Answer:
**X = Atrioventricular septum**

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