1. ERECTION: Is a neurovascular event. It is a complex interplay between somatic and autonomic innervations of penis,the smooth and stimulated musculature of corpora cavernosa. and pelvic floor and the arterial inflow,provided by pair of pudendal arteries Nitric oxide, vasoactive polypeptide,, acetylcholine and prostaglandins, all initiate and contribute to erection.Quality of erection can be expressed by intracavernous pressure.