Ans. c. Both are activated together (Ref: Ganong 24/e p232 Guyton 13/e p699)In response to descending excitatory input to spinal motor circuits, both a- and y-motor neurons are activated"In response to descending excitatory input to spinal motor circuits, both a- and -y-motor neurons are activated. Because of this "a--y coactivation, " intrafusal and extrafusal fibers shorten together, and spindle afferent activity can occur throughout the period of muscle contraction. In this way, the spindle remains capable of responding to stretch and reflexivefy adjusting a-motor neuron discharge "--Ganong 24/e p232"Role of the muscle spindle in voluntary motor activity: To understand the importance of the gamma efferent system, one should recognize that 3 1 percent of all the motor nerve fibers to the muscle are the small type A gamma efferent fibers rather than large type A alpha motor fibers. Whenever signals are transmitted from the motor cortex or from any other area of the brain to the alpha motor neurons, in most instances the gamma motor neurons are stimulated simultaneously, an effect called coaetivation of the alpha and gamma motor neurons. This effect causes both the extrafusal skeletal muscle fibers and the muscle spindle intrafusal muscle fibers to contract at the same time. "--Guyton 13/e p699