Ejaculation

Contrary to popular belief, ejaculation and orgasm are two different events/processes.  

Ejaculation is defined as the forceful expulsion of seminal fluid outside of the body.  Ejaculation consists of two phases: Emission and expulsion.  The first phase involves closure of the urethral sphincters to prevent seminal fluid from entering the bladder.  While the sphincters contract and prevent backflow, prostatic and seminal fluids are ejected and pass from the prostate, seminal vesicles, and vas deferens into the back of the urethrae. Emission depends on the contraction of the muscles surrounding the prostate, seminal vesicles, and vas deferens and this can be voluntarily controlled.  However, once semen reaches a certain point (the urethra) then ejaculation can no longer be controlled and is inevitable.

The second phase is expulsion. Expulsion occurs when there is passage of seminal fluid from the urethra through urethral meatus (urethral opening) and out of the body. The expulsion phase is thought to be from the spinal cord and the spinal generator for ejaculation. Expulsion depends on the strong rhythmic contraction of the pelvic floor muscles that occur in 0.8s intervals. On average, 10-15 rhythmical contractions occur per ejaculation. The rhythmic contraction are very pleasurable and part of the sensation of an orgasm.

The control of ejaculation is a complex interaction between the brain, spinal cord, peripheral nervous system (nerves that go from the spinal cord to other areas of the body), hormones, muscles, and the vascular system.

Neurotransmitters are chemicals released at the end of the nerve that then stimulate or “talk to” the next nerve. Neurotransmitters are how nerves communicate within the body. There are various types of neurotransmitters. Dopamine, serotonin, and nitric oxide are neurotransmitters involved in ejaculation. Dopamine stimulates ejaculation. In fact, studies have found that when dopamine is injected into anesthetized rats, they are able to ejaculate! The neurotransmitters, Sertonin and nitric oxide can inhibit or prevent ejaculation.

Hormones influence ejaculation as well.  The hormone oxytocin has been shown to increase after male ejaculation.  Oxytocin can also increase the amount of ejaculated sperm and improve sperm motility! Thyroid stimulating hormone plays an important role in premature ejaculation; increased TSH can result in premature ejaculation and thus can be associated with hyperthyroidism.  Estrogen plays a role in sperm concentration. Low testosterone can be associated with delayed ejaculation and higher levels of testosterone are associated with premature ejaculation.

What’s interesting is that ejaculation and orgasm are different!  If you have your prostate removed, then you will have dry ejaculate (absence of fluid), but still be able to orgasm and feel sensations of pleasure! 

Ejaculation is an intricate balance between different physiological functions: hormones, nerve stimulation both around the genitals and in the brain, neurotransmitters, vasculature, and muscles.  All of these must work in synergy for ejaculation to occur.

Stay tuned for next posts on Orgasm and Premature Ejaculation!

References

Clement P, Giuliano F. Physiology and Pharmacology of Ejaculation. Basic Clin Pharmacol Toxicol. 2016;119 Suppl 3:18-25. doi:10.1111/bcpt.12546

Alwaal A, Breyer BN, Lue TF. Normal male sexual function: emphasis on orgasm and ejaculation. Fertil Steril. 2015;104(5):1051-1060. doi:10.1016/j.fertnstert.2015.08.033

Pereira-Lourenço M, Brito DVE, Pereira BJ. Premature Ejaculation: From Physiology to Treatment. J Family Reprod Health. 2019;13(3):120-131.

Lovinger DM. Communication networks in the brain: neurons, receptors, neurotransmitters, and alcohol. Alcohol Res Health. 2008;31(3):196-214.

Corona G, Jannini EA, Vignozzi L, Rastrelli G, Maggi M. The hormonal control of ejaculation. Nat Rev Urol. 2012;9(9):508-519. doi:10.1038/nrurol.2012.147