Overview Male sexual response controlled by the parasympathetic and sympathetic divisions of the autonomic nervous system (ANS) erection ("point") is under control of parasympathetic ANS emission ("shoot") is under control of sympathetic ANS divided into 4 phases: excitement plateau orgasm resolution Excitement and Plateau Erection parasympathetic division of autonomic nervous system control (pelvic nerve) NO → (+) guanylyl cyclase → ↑ cGMP → smooth muscle relaxation and vasodilation pro-erectile (tumescence) mechanism cGMP-specific phosphodiesterase breaks down cGMP and limits vasodilation cGMP-specific phosphodiesterase inhibitors treat erectile dysfunction sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) Orgasm Emission sympathetic division of autonomic nervous system control (hypogastric nerve) movement of ejaculate into prostatic urethra facilitation by peristaltic contractions of vas deferens, seminal vesicles, and prostatic smooth muscles Ejaculation somatic nervous system control (pudendal nerve) movement of ejaculate through urethra and out of penis facilitation by rhythmic contractions of perineal muscles includes ischiocavernosus and bulbospongiosus muscles of penis Seminal fluid seminal vesicle secretions 60% seminal fluid volume fructose, ascorbic acid, prostaglandins, phosphorylcholine, and flavins fructose nourishes spermatozoa prostaglandins induce peristaltic contractions in uterus and fallopian tubes to propel sperm up female reproductive tract prostate secretions 30% seminal fluid volume prostatic acid phosphatase (PAP), prostatic-specific antigen (PSA), fibrinolysin, citric acid, zinc, and phospholipids fibrinolysin liquefies seminal fluid spermatozoa (sperm) 10% seminal fluid volume Resolution Sympathetic division of autonomic nervous system control (hypogastric nerve) NE→ ↑ [Ca2+]in → smooth muscle contraction and vasoconstriction anti-erectile or pro-flaccidity (detumescence) mechanism