Final answer:
A motor unit refers to a single neuron and the skeletal muscle cells it stimulates, which contract when acetylcholine is released at the neuromuscular junction.
Step-by-step explanation:
The term that refers to one neuron and all the skeletal muscle cells it stimulates is a motor unit. Its size can vary depending on the nature of the muscle and the precision required for the muscle's movements.
Muscle contraction is initiated when the brain sends an electrochemical signal to a motor neuron, which then innervates multiple skeletal muscle fibers.
This signal reaches the neuromuscular junction, where the neurotransmitter acetylcholine is released, binds to receptors on the muscle fiber, and causes it to contract.