Final answer:
A motor unit is composed of one motor neuron and all the muscle fibers it innervates, important for muscle contractions and control, with variations in size for different muscular functions.
Step-by-step explanation:
The term for one motor neuron and all the muscle fibers it innervates is known as a motor unit. A motor unit consists of a single motor neuron and the group of muscle fibers it activates. The size and number of muscle fibers in a motor unit can vary greatly, depending on whether the muscle is involved in fine motor control, like the extraocular muscles of the eyes, or in gross movements, such as the quadriceps muscles of the thigh. Large motor units have one motor neuron controlling many muscle fibers for powerful, gross movements, while small motor units have one motor neuron controlling a smaller number of muscle fibers for precise, fine movements.