THE PHYSIOLOGY OF SEXUAL INTERCOURSE (IN BRIEF)
The sexual function in males and females are regulated by a complex interplay between the sympa-thetic, parasympathetic, central, and peripheral nervous systems. During arousal, thoughts, as well as sensory stimulation, stimulate the parasympathetic nerves to alter blood flow and glandular secretions in the genitalia.
When sexually aroused, erection or stiffening of the penis occurs by stimulation of afferent nerves from the genitalia, as well as by nerves from the brain that responds to erotic psychic stimuli. These nerves stim-ulate the efferent nerves located in the lumbar region of the spinal cord. Stimulation of the parasympa-thetic nervous system causes the arterial blood ves-sels to dilate and the smooth muscles to relax, filling the vascular channels with blood. At the same time, veins in the penis are compressed. This blockage in outflow adds to the turgor of the penis. The subse-quent tensing of the skin over the penis further in-creases the sensitivity of the sensory receptors.
The rhythmic stimulation of the sensory receptors during intercourse results in sympathetic stimulation and contraction of the smooth muscles of the repro-ductive tract to push the semen into the urethra. At the same time, the sphincter guarding the urinary bladder contracts, preventing urine from being ex-pelled. This process is known as emission. Soon, the skeletal muscles—ischiocavernosus and bulbospon-giosus—located in the perineum contract, expelling the semen. This process is known as ejaculation. The associated pleasurable sensation experienced is known as orgasm.
In women, similar phases occur. The parasympa-thetic nerves increase blood flow to the genitalia. Lo-cal glands are stimulated to increase their secretions to help with lubrication. Erection of the clitoris helps increase the sensitivity of the area to stimuli. The rhythmic stimulation of the clitoris and vagina, to-gether with other stimuli (touch, smell, auditory), leads to orgasm. Orgasm in females is accompanied by peristaltic contractions of walls of the vagina and uterus and the pelvic muscles.