A written composition on a particular subject intended for publication in a newspaper or magazine. Articles may be based on fact or opinion.
During orgasm, the pelvic muscles – including those that stretch from your pubic bone to your tailbone – contract and tense up in a rhythmic movement called ejaculation. This article will explore what makes these muscles contract.
The bulbocavernosus muscle
The bulbocavernosus muscle is a paired pelvic floor muscle in males that extends forward and wraps around the bulb of the penis. It is sexually dimorphic; it contracts to enclose the anus and genitals in males, while it covers the vaginal orifice in females.
It is important during ejaculation, because it contains blood and pressures the corpus cavernosum urethrae to keep an erection, but can also contract to eject semen through the urethra. This is what causes the pulsing sensations of pleasure at the peak of orgasm. If this muscle isn’t functioning correctly, men may experience ED (erectile dysfunction) and pain during ejaculation.
During ejaculation, it is important that the urethral sphincter and epididymis are tightened to prevent sperm from flowing back into the bladder. This is achieved by a complex series of autonomic and somatic responses, including the autonomic activation of the prostate, seminal vesicles, and epididymis; frictional stimulation on the penile skin; and rhythmic contractions of perineal and pelvic floor striated muscles. In addition, a central pattern generator in the lumbosacral cord integrates and relays genital sensory and motor signals.
Researchers found that the amplitude of these contractions is higher during a regular series of contractions, but that they can be varied from session to session, and that the duration and number of contractions does not correlate with orgasm intensity. This is due to individual variations in the way that the brain interprets and triggers these contractions.
The epididymis
The epididymis is a series of small tubes that collect and store sperm. They are located on the back of each testicle and are a part of the male reproductive system. The epididymis is usually healthy, but it can be infected and inflamed, a condition known as epididymitis.
During ejaculation, the walls of the epididymis contract (squeeze) to create peristaltic waves that transport sperm from the epididymis to the urethra. The urethra is a tube that runs through the penis and transports either sperm or urine.
When a man is sexually stimulated, friction on the glans penis or other stimuli cause nerves to send signals that lead to ejaculation. These signals trigger the muscular contractions in the testicles and the epididymis. The sperm are then released into the vas deferens, which leads to the urethra. The muscles in the urethra contract, propelling the sperm and seminal fluid through the tube.
The epididymis contains a thick pseudostratified columnar epithelium with short stereocilia that reabsorb fluid and concentrate sperm. The epithelium is thinner in the tail region, which is rich in smooth muscle fibers. The epididymis is vascularized by branches of the testicular artery. A number of studies have demonstrated that gene expression in the epididymis is carefully regulated in a region-specific manner. This is especially true in the corpus and cauda regions.
The seminal vesicles
The seminal vesicles (also called vesicular glands) are paired tubular organs located posteroinferior to the prostate. They are filled with a yellowish-white viscous fluid that makes up 50 to 80% of semen and have short excretory ducts that empty into the prostatic urethra.
The walls of the seminal vesicles are composed of smooth muscle and tall columnar epithelium that forms branching mucosal folds that stretch when the vesicle is distended by large amounts of secretory material (see figure 2.3.39). The vesicles also contain a honeycombed structure with complex folding to produce irregular anastomosing channels that extend into the central cavity of the vesicle.
The vesicles are innervated by the parasympathetic pelvic nerve, which sends fibers to the ejaculation structures (including the levator ani and ischiocavernosus muscles and the bulbourethral sphincter) from its preganglionic parasympathetic neurons in the sacral parasympathetic nucleus. The motor component of the pudendal nerve then projects these fibers to the aforementioned muscles, which contract during ejaculation to propel the semen through the urethra. In contrast, the adrenergic nerves of the bladder send fibers to the ejaculatory structures from their preganglionic nerves in the superior pudendal nerve (also known as the spinal adrenoceptors). Thus, during ejaculation, contractions of both the bladder and the seminal vesicles occur simultaneously.
The bladder
When the bladder fills up, the walls stretch and this is sensed by the bladder afferent neurons which relay the information to the brain. This information is then used to initiate urination.
During ejaculation, the muscles in the pelvic area contract several times. The anal and urinary sphincters, the prostate gland, and the seminal vesicles contract in a rhythmic sequence and sperm is then ejected out of the penis via the vas deferens and into the urethra. During ejaculation, a man may also release fluid from the prostate and seminal vesicles called precum. This is often clear and different from semen and can be detected at the tip of the penis.
The prostate gland is located in the neck of the urinary bladder. It is a triangular-shaped area, with the apex pointing upwards. Urine enters the bladder through the left and right ureters which are connected to the urethra. The opening into the urethra is sealed by a band of the detrusor muscle.
The apex of the bladder has an opening that is covered by small flaps of mucosa which act as valves, allowing urine to enter but preventing it from backing up into the ureters. When a person is urinating, parasympathetic input to the detrusor muscle is inhibited and there is activation of sympathetic and somatic afferent pathways which causes the two urethral sphincters to contract.
See Also:
