double innervation, innervation of effector organs by fibers of the sympathetic and parasympathetic divisions of the autonomic nervous system. The pelvic viscera, bronchioles, heart, eyes, and digestive system are all doubly innervated. The fibers of the two divisions operate at cross-purposes to achieve a state of balance and maintain constancy in the body’s internal environment. The mode of action of each division varies. In some structures one division is stimulating and the other inhibiting; in others, separate fibers from each division act to stimulate and inhibit complementary function.
