8.2 Autonomic Control of Sex Flashcards
What type of reflex is the sexual reflex
Involuntary
Describe the afferent part of the sexual reflex
Sensory stimuli such as special senses (e.g hearing or vision), sexual fantasy, non genital erogenous areas (e.g nipples or neck) or external genitalia
What are the phases of the efferent part of the sexual reflex
erection, emission, ejection and orgasm
What are the 2 components of ejaculation
emmision and ejection
Describe the sensory innervation to the external genitalia
The pudendal nerve supplies sensory innervation to the external genitalia for both men and women. For the external genitalia, the penis is equivalent to the clitoris and the scrotum is equivalent to the labia majora
Describe the erectile tissue is males and females
In males and females, the primary erectile tissue is the corpora cavernosa. These tissues are supplied by branches of the internal pudendal artery. The blood then drains from the cavernous sinuses into the deep dorsal vein
Describe the autonomic control of erection
In the autonomic control of erection, erection is achieved by increased blood flow to the corpora cavernosa, relaxation of smooth muscle of the cavernous sinuses and compression of veins preventing venous return. These responses are controlled by parasympathetic nerves, that use nitric oxide instead of acetylcholine. The nitric oxide activates guanylate cyclase which converts GTP to cyclic GMP, this cGMP causes smooth muscle relaxation and the relaxation of the venous cavernous sinusoids leads to erection.
Describe the maintenance of the erection via somatic control
Maintenance of erection is assisted by the contraction of the perineal muscles ischiocavernosus and bulbospongiosus, these are supplied by the somatic nervous system.
Describe the mechanism of Sildenadil (aka Viagra)
It inhibits the effects of phosphodiesterase-5, PDE5 causes hydrolysis of cGMP to GMP which is then phosphorylated to GTP, hence inhibition of PDE5 increases cGMP levels, this cGMP will cause smooth muscle relaxation. This enhances the relaxation of the venous sinusoids and promotes erection
What is emission in males
In males, emission is the release of secretions by the vas deferens, prostate, seminal vesicles and bulbourethral (Cowper’s) glands into the penile urethra
What is emission in females
In females, emission is the release of secretions by the bulbovestibular (Bartholin’s) glands into the vagina
Describe the nervous control of emission
Emission is under sympathetic control, to stimulate contraction of smooth muscle walls of glands to release secretion.
Also there is contraction of the internal urethral sphincter in males which prevents retroejaculation
Describe ejection in males
In males ejection of seminal fluid from the penile urethral is achieved by rhythmic contractions of bulbospongiosus muscles which are innervated by somatic motor neurons of the pudendal nerve
What is the nature of ejection in females
In females there is debate over the nature of ejection and it is believed that there is release of a small amount of fluid from Skene’s glands either side of the urethral that contains prostate specific antigens
What is an orgasm
An orgasm is associated with powerful pelvic and perineal muscle contractions that are interpreted as pleasurable by the brain.
It is also associated with hyperventilation and increased heart rate/BP.
In males it is followed by a refractory period where erections and ejaculation is inhibited but this is not the case in females.
What is oxytocin
Oxytocin is a hormone that is released during orgasm in humans and is produced in the hypothalamus
Describe how an erection subsides
Following ejaculation, the sympathetic nervous system causes vasoconstriction and contraction of smooth muscle of the corpora cavernosa. This reduces inflow of blood and relieves pressure on the veins, allowing for the subsidence of an erection
What is priapism
Priapism is the failure of an erection to subside, which can cause painful ischemia of the corpora cavernosa
Describe how spinal cord injuries can affect the sex reflex
As ejection and ejaculation is a spinal cord reflex, paraplegic men with spinal cord injuries above S2 have erectile responses to penile stimulation and paraplegic men with lesions above T11 may also exhibit emission. The ejection is dependent on the sympathetic nerve supply to the internal urethral sphincter
