If a cell receives a signal to contract, then its neighbours are also stimulated to contract. This is due to the presence of-

Options

A. tight junctions
B. sarcoplasm
C. desmosomes
D. intercalated disc

Answer

To solve the question, we need to identify the structure that allows neighboring cells to contract simultaneously when one cell receives a signal to contract.

### Step-by-Step Solution:

1. **Understanding Cell Communication**:
- Cells in tissues often need to communicate with each other to coordinate their functions. In muscle tissue, for instance, when one muscle cell (myocyte) receives a signal to contract, it is crucial that neighboring cells also contract to produce a coordinated movement.

2. **Evaluating the Options**:
- **Tight Junctions**: These are structures that prevent the passage of materials between cells. They do not facilitate communication or contraction signals between cells. Therefore, they are not the correct answer.
- **Sarcoplasm**: This is the cytoplasm of muscle cells. While it plays a role in muscle function, it does not directly facilitate the signaling for contraction between neighboring cells. Thus, this option is incorrect.
- **Desmosomes**: These structures provide mechanical strength to tissues by anchoring cells together. They do not allow for the transmission of contraction signals between cells, making this option incorrect as well.
- **Intercalated Discs**: These are specialized connections between cardiac muscle cells. They contain gap junctions that allow for the direct passage of ions and signaling molecules between cells. This enables neighboring cells to contract in unison when one cell is stimulated.

3. **Conclusion**:
- The presence of **intercalated discs** allows for the coordinated contraction of cardiac muscle cells. When one cell receives a signal to contract, the signal is transmitted through the intercalated discs, stimulating neighboring cells to contract as well. Therefore, the correct answer is **intercalated discs**.

### Final Answer:
- The correct answer is **intercalated discs**.

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