The physiology of human sexual function

The terminology for the complexities of human sexual activity is discussed and the male and female sexual arousal to orgasm is described with its underlying physiological mechanisms. The original four-phased human sexual response cycle of Masters & Johnson (Excitation, Plateau, Orgasm, Resolution) is now modified by amalgamation of the plateau phase into the excitation phase and the addition of two desire phases, one spontaneous (proactive) the other activated by arousal per se (reactive). The relation between genital arousal and subjective arousal is reviewed for males and females. In males, erection and subjective arousal usually have good concordance but in females increased vaginal blood flow and lubrication can occur without any concomitant subjective arousal even with sexually aversive stimuli. The subjective feeling of sexual arousal in women is now regarded as more complex than stimuli from the genitals, involving the contextual meaning and content of the stimuli. Imaging studies have revealed multiple areas of the brain that become involved during sexual arousal and at orgasm. However, different studies using different techniques and analyses have given conflicting accounts of which areas are activated and which are deactivated, and it is not possible at present to finalize the position.