Answer:
The answer is B: All the muscle cells innervated by a single motor neurorn.
Explanation:
It is called a motor unit, all muscle fibers that are innervated by a motor neuron cell. A motor neuron cell can establish contact with up to 150 muscle fibrils, which when activated causes their simultaneous contraction, therefore, all the muscle fibers of a motor unit contract and relax at the same time.
