THE MALE RESPONSE
The penis introduces sperm into the vagina. There are two types of tissue: 2 masses of corpora cavernosa penis which are rich in blood vessels & the urethra-containing corpus spongiform penis. The release of nitric oxide causes the relaxation of smooth muscle that results in vasodilation; as blood enters the penis stiffens which blocks the veins allowing the release of the blood. During stimulation, large quantities of blood enter causing the tissue to swell. The penis ranges in size from 4.7 to 9.2 inches. Smaller penises have a greater enlargement upon arousal (Jones, 1991).
The male sexual response involves diverse regions of the nervous system.
Initially, the parasympathetic division of the ANS is required for arousal
and sympathetic stimulation (through stress, anxiety, fear) will inhibit
erection. During emergencies, blood is directed towards muscles and
away from the reproductive system. During ejaculation however, the sympathetic
division is engaged and, through NE release, it mediates emission (by
the release of the components of the prostate, seminal vesicle, and
vas deferens), contraction of the urethral sphincter, and the propulsion
of semen into the penile urethra. In addition to the components of the
ANS, somatic innervation through the pudendal nerve causes the rhythmic
contractions of bulbocavernosus and other muscles which expel the ejaculate
Impotence is most commonly caused by the ability to maintain an erection;
may be caused by depression, anxiety (most cases are psychological),
drugs & illnesses that affect ANS, or plaques blocking arteries.
Temporary periods of impotence are common in normal individuals.
During intercourse, reflexes stimulate peristalsis of the testes, epididymis,
vas deferens, seminal vesicles, prostate gland.
THE FEMALE RESPONSE
The vagus nerves offer an alternate route through which women with spinal cord injury can perceive vaginal stimulation and reach orgasm, utilizing the same brain regions identified in normal women (such as the medial amygdala, hypothalamus, frontal and parietal cortex, and the cerebellum) (Komisaruk, 2004).
Free nerve endings are located in the wall of the outer third of the vagina which are sensitive to stimulation. The majority of the vagina has very little nervous supply; most female stimulation from friction against walls of exterior vaginal opening.In the absence of sexual arousal, the vagina receives little blood supply. During arousal, vaginal blood supply increases, blood is retained in the vaginal wall (congestion), and fluid leaks through intercellular channels into the vaginal lumen. In the lumen, the fluid mixes with proteins released by the cervix to produce a lubricating fluid. Vaginal congestion occurs in the anterior third of the vagina (Mah, 2001). The vaginal epithelia maintains sodium which allows it to reabsorb fluid quickly (Jones, 1991; Levin, 2007).
The vagina measures and average of 4 inches but this increases during arousal and can even be increased voluntarily. (Jones, 1991). There are two layers of smooth muscle in the vagina: the inner longitudinal layer contracts to make it shorter and wider while the outer circular layer can constrict the vagina (Levin, 2007). As arousal continues, the uterus pulls away from the vaginal wall (vaginal "tenting") and the vagina expands at its distal end (Levin, 2007).
After childbirth, vaginal wall may relax and provide less stimulation during intercourse. Exercises and different sexual positions may help (Jones, 1991).
Durint stimulation, the clitoris becomes wider and the vaginal walls darken. In plateau phase, clitoris retracts and is coverd by its hood (Jones, 1991).
THE "G SPOT"
THE UTERUS AND VULVA
During intercourse, the uterus becomes larger because of increase blood flow. The labia minora become larger and the breasts can increase their size by 25% (Jones, 1991). Uterine contractions become rhythmic, perhaps caused by oxytocin (Jones, 1991).