The nervous system is divided into three components: the central nervous system, which includes the brain, the brainstem and the spinal cord, the peripheral nervous system, which includes the receptors sensory muscles and effector organs of the body and the autonomic nervous system which is part of both the peripheral and central nervous systems and controls visceral and largely unconscious functions (Barker & Barasi, 2005). The sexual response activates all these systems. (a) The central nervous system, (b) The peripheral nervous system (a) The autonomic nervous system controls smooth muscles and secretions in all male reproductive organs (Dail, 1993). This includes the parasympathetic and sympathetic systems discussed later. It is part of the peripheral nervous system but many also consider it part of the central nervous system. For the purposes of this essay, it will be included in the section with the peripheral nervous system. This essay will explore the time course of penile arousal and erection, starting from the supraspinal level, i.e. the cerebral component of the central nervous system. and following it up to the post-ganglionic mechanisms of penile erection through the action of the peripheral and autonomic nervous system. It should be noted that this is not the only route by which erection can occur: reflex erections can occur from stimulation of the penis via a single-step afferent pathway that bypasses the autonomic system and most of the brain system, but this will not be discussed at this time. However, most erections are a combination of these two pathways (Steer, 2000), so subsequent consideration of this second pathway may prove prudent. Central nervous systemThe normal psychogenic pathway...... half of the article...... electal muscles, including the larynx and pharynx. The sacral areas of the PNS are most closely linked to sexual arousal and activity. The sacral plexus, which includes sacral nerves S2–S4, innervates the genitals (Lue et al., 1983), with preganglionic neurons running from the pelvic nerves to the pelvic plexus where they meet sympathetic neurons and fuse to form the cavernous nerves (Steer, 2000). These cavernous nerves exit the pelvic plexus through the pelvic fascia, fuse with the prostatic capsule, and enter the penis through a variety of routes, including through the levator ani and urethra, entering the corpus spongiosum or crura of the penis. The PNS also receives information from the somatic pudendal nerve, which receives sensory information from the penis and also innervates it, as well as possibly from afferents from the hypogastric nerve (Rosen & Sachs, 2000).