Which of the following is an example of multiunit smooth muscles ?

Options

A. Smooth muscle with blood vessels
B. Smooth muscle with intestine
C. Masseter muscles of the jaw
D. Arrector pili muscle of skin

Answer

To answer the question "Which of the following is an example of multiunit smooth muscles?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Types of Smooth Muscles**:
- Smooth muscles are classified into two main types: single-unit smooth muscles and multi-unit smooth muscles.
- Single-unit smooth muscles work together as a single unit, while multi-unit smooth muscles operate independently.

2. **Identify Characteristics of Multi-Unit Smooth Muscles**:
- Multi-unit smooth muscles do not have gap junctions, which means they are not electrically coupled and can function independently.
- This independence allows for more precise control over muscle contractions.

3. **Examples of Smooth Muscles**:
- Single-unit smooth muscles include those found in the gastrointestinal tract, blood vessels, and jaw muscles.
- Multi-unit smooth muscles include the erector pili muscles of the skin, which are responsible for causing hair to stand up (goosebumps).

4. **Evaluate the Options**:
- If the options provided include the erector pili muscle, that would be the correct answer as it is a classic example of multi-unit smooth muscle.
- Other options may include muscles from the gastrointestinal tract or blood vessels, which are examples of single-unit smooth muscles.

5. **Select the Correct Answer**:
- Based on the characteristics and examples discussed, the correct answer is the option that lists the erector pili muscle of the skin.

### Final Answer:
The example of multi-unit smooth muscles is the **erector pili muscle of the skin**.

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