An erection does not occur on demand at a snap of the fingers. Several systems in the body and the mind team up to produce an erection. The anatomy of the penis is the foundation, but erection has certain other prerequisites: an intact neurovascular system, absence of medical or psychogenic disturbance, confidence, intimacy, receptivity, excitement, and physical attraction. Physical and psychological stimulation are also required. If any of the involved mechanisms fail, an erection can become difficult or impossible to achieve or to maintain, resulting in erectile dysfunction (ED).
The normal male sexual response
The normal human male response to sexual opportunity, comprises five phases: desire, excitement, plateau, orgasm, and refraction, as follows:
- A healthy and sexually functional man, who is mentally prepared for and interested in sexual activity, feels the desire to engage in lovemaking.
- When that desire is accompanied by sexual stimulation, excitement occurs. The man becomes aroused and his penis becomes erect. Additionally, his pulse rate and blood pressure and nipple sensitivity increase.
- Arousal increases and the man reaches a high plateau of sexual pleasure, associated with physiological changes such as rapid breathing, further testicular elevation and swelling, and generalized muscle relaxation.
- Plateau is followed by semen emission and ejaculation, together with various associated sensations perceived in his brain as pleasurable, called orgasm.
- The final phase is the refractory period, characterized by the gradual disappearance of all other physiological signs of arousal, and during which no erection or orgasm can occur.