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There are 4 main components of male sexual function
Sexual dysfunction is a problem with one of these components that interferes with interest in or ability to engage in sexual intercourse. Many drugs and numerous physical and psychologic disorders affect sexual function.
Libido:
Libido is the conscious component of sexual function. Decreased libido manifests as a lack of sexual interest or a decrease in the frequency and intensity of sexual thoughts, either spontaneous or in response to erotic stimuli. Libido is sensitive to testosterone levels as well as to general nutrition, health, and drugs. Conditions particularly likely to decrease libido include hypogonadism (see Male Reproductive Endocrinology and Related Disorders: Male Hypogonadism), uremia, and depression. Drugs that sometimes decrease libido include weak androgen receptor antagonists, such as spironolactone or cimetidine, and virtually all drugs that are active in the CNS, such as SSRIs, tricyclic antidepressants, and antipsychotics. Loss of libido due to SSRIs or tricyclic antidepressants sometimes is reversible with the addition of bupropion or trazodone.
Erection:
Erection occurs as the result of a complex neuropsychologic process. Higher cortical input and a sacrally mediated parasympathetic reflex arc combine to stimulate erection. Nerve output travels through the pudendal nerves, which traverse the posterolateral aspect of the prostate. Terminating in the penis, these nonadrenergic, noncholinergic nerves activate nitric oxide synthase, producing nitric oxide, which relaxes smooth muscle lining the sinusoidal spaces that connect the arterioles and venules within the corpus cavernosa. The blood flow within the sinusoids increases markedly, distending them and compressing the venules, causing veno-occlusion. The increased inflow and veno-occlusion together produce penile rigidity. Many factors affect the ability to have an erection (see Male Sexual Dysfunction: Erectile Dysfunction).
Ejaculation and orgasm:
Ejaculation is controlled by the sympathetic nervous system. α-Adrenergic stimulation causes contractions of the epididymis, vas deferens, prostate, and muscles of the pelvic floor. In addition, the neck of the bladder closes, preventing retrograde ejaculation of semen into the bladder. SSRIs may delay or inhibit ejaculation.
Orgasm is the highly pleasurable sensation that occurs in the brain generally simultaneously with ejaculation. Anorgasmia may be a physical phenomenon due to decreased penile sensation (eg, from neuropathy) or a neuropsychologic phenomenon due to psychiatric disorders or psychoactive drugs.
Ejaculatory insufficiency is reduced or absent semen volume that may result from retrograde ejaculation or interruption of sympathetic stimulation. Retrograde ejaculation is common in men with diabetes and can also be caused by surgery on the neck of the bladder or transurethral resection of the prostate. Sympathetic interruption, either from surgery or with drugs (eg, guanethidine, phentolamine, phenoxybenzamine, thioridazine), diminishes ejaculatory volume.
Premature ejaculation is ejaculation occurring sooner than desired by the man or his partner. It is usually caused by sexual inexperience, anxiety, and other psychologic factors instead of disease. It can be treated successfully with sex therapy and SSRIs.
Last full review/revision January 2010 by Bradley D. Anawalt, MD
Content last modified January 2010
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