In which category of muscle fibers, contraction can be
regulated by acetylcholine neurotransmitter ?

Options

A. Skeletal muscle fibers
B. Cardiac muscle fibers
C. Smooth muscle fibers
D. all of these

Answer

To determine which category of muscle fibers has contraction regulated by the acetylcholine neurotransmitter, we can follow these steps:

### Step-by-Step Solution:

1. **Identify Muscle Fiber Types**: There are three main types of muscle fibers: skeletal muscle fibers, cardiac muscle fibers, and smooth muscle fibers.

2. **Understand the Role of Acetylcholine**: Acetylcholine is a neurotransmitter that plays a crucial role in the communication between nerve cells and muscle fibers. It is released at the neuromuscular junction.

3. **Examine Skeletal Muscle Fibers**: Skeletal muscle fibers are under voluntary control and are directly influenced by the nervous system. When a nerve impulse reaches the neuromuscular junction, acetylcholine is released, which binds to receptors on the skeletal muscle fibers, leading to muscle contraction.

4. **Evaluate Cardiac Muscle Fibers**: Cardiac muscle fibers are involuntary and are regulated by the autonomic nervous system and hormones, rather than directly by acetylcholine.

5. **Assess Smooth Muscle Fibers**: Smooth muscle fibers are also involuntary and are primarily regulated by the autonomic nervous system, hormones, and local factors, but not directly by acetylcholine in the same manner as skeletal muscle.

6. **Conclusion**: Based on the above analysis, skeletal muscle fibers are the category of muscle fibers where contraction can be regulated by the acetylcholine neurotransmitter.

### Final Answer:
The category of muscle fibers in which contraction can be regulated by acetylcholine neurotransmitter is **skeletal muscle fibers**.

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