• Male sexual response
    • male sexual response is 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
    • male sexual response is divided into 4 phases:
      1. excitement
      2. plateau
      3. orgasm
      4. 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)
  • 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
3. 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

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