Male Sexual Response

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