A single neuron and all the muscle fibers it stimulates comprise a:

• A. sarcomere
• B. motor unit
• C. myofibril
• D. neuromuscular junction

Answer: (B)

Verified step by step guidance

1. Understand the anatomy of a motor unit: A motor unit consists of a single motor neuron and all the muscle fibers it innervates. This is the functional unit of muscle contraction.
2. Review the role of the neuromuscular junction: This is the site where the motor neuron communicates with the muscle fiber, but it is not the entire motor unit. It is a part of the motor unit.
3. Clarify the term sarcomere: A sarcomere is the smallest contractile unit within a myofibril, but it does not include the neuron or the muscle fibers stimulated by the neuron.
4. Define myofibril: Myofibrils are the thread-like structures within muscle fibers that contain sarcomeres. They are part of the muscle fiber but do not include the neuron.
5. Conclude that the correct term for a single neuron and all the muscle fibers it stimulates is 'motor unit,' as it encompasses both the neuron and the muscle fibers it innervates.