A motor unit consists of a single motor neuron and all the muscle fibers it innervates. When the motor neuron sends a signal, all the muscle fibers in that unit contract simultaneously. This coordinated action allows for precise control of muscle movements. Motor units vary in size and function. Smaller motor units, which control fewer muscle fibers, are typically found in muscles requiring fine motor skills, like those in the hands. Larger motor units, which control many fibers, are found in muscles responsible for powerful movements, such as those in the legs.