We already saw that the afferent axons of the muscle spindle help to maintain limb position even when the load Carried by the limb is altered. Efferent control of the muscle spindles permits these muscle length detectors to assistin changes in limb position as well. Consider a single muscle spindle. When its efferent axon is completely silent, the spindle is completely relaxed and extended. As the firing rate of the efferent axon increases, the spindle gets shorter and shorter. If, simultaneously, the rest of the entire muscle also gets shorter. there will be no stretch on the central region that contains the sensory ending, and the aferent axon will not respond. However, if the muscle spindle contracts faster than does the muscle as a whole, there will be a considerable amount of afferent activity.