Penile erection is managed by two different mechanisms. The first one is the reflex erection, which is achieved by directly touching the penile shaft and the second is the psychogenic erection, which is achieved by erotic stimuli. The first one uses the peripheral nerves and the lower parts of the spinal cord, whereas the second one uses the limbic system of the brain. In both conditions an intact neurologic system is required for a successful and complete erection. Stimulation of penile shaft by the nervous system gives rise to the secretion of nitric oxide (NO), which causes the relaxation of smooth muscles of corpora cavernosa (the main erectile tissue of penis), subsequently giving rise to penile erection. Additionally, adequate levels of testosterone (produced by the testes) and an intact pituitary gland are required for the development of a healthy male erectile system. As can be understood from the mechanisms of a normal erection, impotence may develop due to hormonal deficiency, disorders of the neurologic system, lack of adequate penile blood supply or psychological problems.