Ejaculation physiology

Ejaculatory physiology

• during sexual activity, rising levels of arousal reach a threshold that triggers the ejaculatory response
  • rhythmic contractions of the ischiocavernosus and bulbospongiosus muscles as well as semen expulsion are mediated by sensory neurons in the pelvis
    • events are associated with the occurrence of orgasmic climax, a distinct cortical event that is experienced both cognitively and emotionally
• latency to ejaculation, i.e. the time and degree of stimulation required for ejaculation, varies significantly among men and even for individual men in different situations
  
  
• ejaculatory reflex is a complex neurobiological event, involving a coordination of actions in the central and peripheral nervous systems to bring about synchronized neurological and muscular responses
  • spinal ejaculatory centers receive input from supraspinal regions (cognitive arousal), as well as from peripheral sensory afferents from the genitals
    • a spinal control center, referred to as a spinal pattern generator, coordinates sympathetic, parasympathetic and motor (somatic) outflows, integrating the latter with the inputs from the supraspinal sites in the brainstem, hypothalamus and preoptic area
      
      
  • subsequent ejaculatory process is typically divided into two distinct phases that occur in sequence: emission and expulsion
    • first of these phases, emission
      • is initiated by the thoracolumbar sympathetic nerves, which exit the spinal cord at the levels T10-L2
        • nerves initiate peristaltic contraction of smooth muscle in the epididymis, vas deferens, seminal vesicles and prostate
        • actions propel sperm through the male excurrent ductal system into the ejaculatory ducts and urethra. Contractions of smooth muscle within the seminal vesicles simultaneously propel seminal fluid through the ejaculatory ducts
        • ultimately, a bolus of sperm, seminal fluid and prostatic fluid are deposited into the posterior urethra
          • forceful contraction of the bladder neck prevents ejaculate from flowing retrograde into the bladder
    • the second phase of ejaculation, expulsion - distention of the posterior urethra by the seminal fluid bolus stimulates a reflex arc that triggers
      • pudendal nerve, which originates from the sacral spinal cord (S2-S4), mediates involuntary rhythmic contractions of striated peri-urethral (ischiocavernosus and bulbospongiosus) and pelvic floor muscles. Meanwhile, relaxation of the external urinary sphincter occurs
      • end result is rhythmic, forcible ejection of seminal fluid from the posterior urethra towards the urethral meatus
        
        
• failure of the initial step, emission, leads to anejaculation. Inadequate bladder neck closure leads to failure of the second step, expulsion, which defines retrograde ejaculation

Reference:

• 1) Barazani Y et al. Management of ejaculatory disorders in infertile men.Asian J Androl. 2012 Jul;14(4):525-9.