From Wikipedia: "An orgasm (sexual climax) is the conclusion of the plateau phase of the sexual response cycle, and may be experienced by both males and females. Orgasm is characterized by intense physical pleasure, controlled by the involuntary, or autonomic, nervous system.[1] It is accompanied by quick cycles of muscle contraction in the lower pelvic muscles, which surround the primary sexual organs and the anus. Orgasms are often associated with other involuntary actions, including muscular spasms in other areas of the body, a general euphoric sensation, and, frequently, vocalizations. After orgasm, humans often feel tired and a need to rest. This is attributed to the release of prolactin.[2] Prolactin is a typical neuroendocrine response in depressed mood and irritation.[3] Ongoing research at the University Medical Center of Groningen, the Netherlands, studies brain events that accompany orgasm in men and women. Techniques used involve Positron Emission Tomography (PET) and fMRI. Male and female brains act almost the same during orgasm. Brain scans showed that large parts of the cerebral cortex temporarily reduced their activity.[4]" More here: http://en.wikipedia.org/wiki/Orgasm