Innervation of the male reproductive organs. The penis is under the complete control of the central nervous system (CNS), both during arousal and at rest. Many regions of the brain contribute to male sexual response; the hindbrain deepens breathing and the cerebral cortex contributes to the concoction of erotic fantasies. During arousal, excitatory signals from the brain spur nerves in the penis to release chemicals, which signal the smooth muscles of the arteries to relax and fill with blood, resulting in an erection.