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 regarding why neighboring cells contract when one cell receives a signal to contract, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Context**: The question pertains to muscle cells and their ability to contract in response to a signal. This is a characteristic feature of certain types of muscle tissue.

2. **Identify the Types of Junctions**: The question mentions several types of cellular junctions:
- **Tight Junctions**: These junctions prevent the passage of ions and molecules between cells, thus they do not facilitate communication for contraction.
- **Sarcoplasm**: This is the cytoplasm of muscle cells, but it does not play a role in cell-to-cell signaling.
- **Desmosomes**: These are junctions that provide mechanical stability but do not facilitate the transmission of electrical signals necessary for contraction.
- **Intercalated Discs**: These are specialized structures found in cardiac muscle cells that contain gap junctions and desmosomes.

3. **Focus on Intercalated Discs**: Intercalated discs are crucial for the synchronized contraction of cardiac muscle. They contain gap junctions that allow ions and electrical signals to pass directly from one cell to another, facilitating coordinated contraction.

4. **Conclusion**: The presence of intercalated discs allows neighboring cardiac muscle cells to be stimulated to contract when one cell receives a contraction signal. Therefore, the correct answer is **intercalated discs**.

### Final Answer:
The presence of **intercalated discs** allows neighboring cells to contract when one cell receives a signal to contract.

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