Ejaculation is a complex process coordinating neurophysiological events and muscular contractions, mediated by both spinal afferent and efferent reflexes and higher cortical input.
Higher cortical input is a complex network controlling other aspects of sexual response. Cholinergic, adrenergic, GABA and oxytocin are involved – but primarily mediated by dopamine and serotonin.
Dopamine promotes ejaculatory response (dopamine delivers)
Serotonin inhibits ejaculatory response (serotonin suppresses)
3 synchronised phases:
Emission
Expulsion of sperm and seminal fluid into posterior urethra
Mediated by T10 – L2 pathways, primarily sympathetic
Simultaneous closure of bladder neck and external sphincter
Ejection (expulsion)
Antegrade expulsion of semen via the urethra
Mediated by somatic nerves (perineal branch of pudendal nerve) S2 – S4
Pulsatile contractions of bulbospongiosus, ischiocavernosus and levator ani
Relaxation of the external sphincter
Orgasm
Cerebral processing of the pudendal nerve stimuli resulting from increased pressure in posterior urethra, sensory stimuli around veru and contraction of the bulbar muscles