Final answer:
Large motor units are used for simple tasks requiring gross movements, such as extending the knee, while small motor units are involved in precise fine motor skills such as eye movements or manipulating objects with fingers.
Step-by-step explanation:
To perform simple tasks, such as powerfully extending the knee joint, large motor units are typically used. These motor units consist of a single motor neuron supplying a large number of muscle fibers, which allows for gross movements that do not require fine motor control.
On the other hand, small motor units are associated with fine movements, such as those involved in manipulating objects with the fingers or making precise eye movements. The extraocular muscles controlling eye movements are an example, where very few muscle fibers are supplied by a single motor neuron, allowing for precise but not forceful actions. In contrast, muscle groups like the quadriceps are comprised of large motor units to facilitate powerful contractions.
Different muscles have different sizes of motor units to provide the necessary control. Fine motor skills involve small motor units for precision, while gross motor skills engage large motor units for larger, more forceful movements.