Until recently, research on aging has focused mainly on crucial things that go wrong - on heart disease, mental decline, arthritis, prostate woes, and the like. But while big-ticket items are still getting the priority they deserve, researchers are also expanding their horizons to include less critical issues. Sexuality is an important example. Several reports shed light on aging and sexuality, and one of them suggests that sex itself may help prevent sexual dysfunction in older men.
At any age, sexual activity is an instinctive, automatic part of human behavior. But the biology behind that behavior is quite complex.
Although the sex act is a continuous process, researchers have divided it into six stages. The first necessity is sexual desire or libido. The normal sex drive is a prime example of the unity of mind and body. It requires both an appropriate mindset and sufficient amounts of the male hormone testosterone. Sexual desires surface in puberty, when testosterone levels rise; although ardor tends to wane with age, most men produce enough testosterone to maintain libido throughout life. At any stage of life, however, worry, stress, or depression can thwart sexual interest, even if a man's physical apparatus remains intact.
Sexual activity itself begins with a state of arousal that results from various combinations of erotic thoughts and sensory stimulation that may involve the senses of touch, sight, scent, taste, or hearing. An area of the brain called the hypothalamus co-ordinates erotic images and sensations and transmits the impulses of desire through the spinal cord to the pelvis, where they link up with the nerves of the autonomic nervous system; sensory nerves from the skin of the penis and other erogenous zones connect directly to the autonomic nerves without involving the brain.
When properly stimulated, the autonomic nerves in the pelvis spring into action. They start the second stage of the male sexual response by transmitting chemical signals to the arteries of the penis, causing them to widen and admit more blood. Blood rushes into the two corpora cavernosa, shafts of spongy tissue that contain many vascular channels. The corpora cavernosa swell, producing an erection. The engorged corpora also put pressure on venules, compressing and narrowing them to prevent the extra blood from leaving, so the erection can be maintained.
For years, doctors have known that an erection is a hydraulic event that depends on a sixfold increase in the amount of blood in the penis. But research has revealed that an erection is also a chemical event. A tiny chemical called nitric oxide allows nerves to communicate with each other and with the arteries of the penis. Nitric oxide acts on the arteries through an intermediary called cyclic guanosine monophosphate (cGMP). It's been an exciting discovery for scientists, and it led to important progress for men with erectile dysfunction (ED) since the ED pills (Cialis, Levitra, and Viagra) act by boosting cGMP levels in the penis.
The third stage of sexual activity is called the plateau, which usually lasts from 30 seconds to two minutes. The heart rate and blood pressure rise as sexual activities continue, pumping more blood to the body's tissues. The penis is not the only recipient of increased blood flow; most men also experience facial flushing, and the testicles themselves swell by about 50%. During the plateau phase, the prostate and seminal vesicles begin to discharge fluid in preparation for ejaculation.
Sexual excitement climaxes with the fourth stage, ejaculation. The autonomic nervous system is in charge here, too. It tells the muscles in the epididymis, vas deferens, seminal vesicles, and prostate to contract, propelling semen forward. At the same time, nerve impulses tighten muscles in the neck of the bladder so that semen is forced out through the urethra instead of flowing back into the bladder. Ejaculation is usually accompanied by the pleasurable sensation of orgasm; in nearly all men, the heart rate reaches its peak during ejaculation.
All good things come to an end. The fifth stage of sexual activity is detumescence, when the penis returns to its flaccid state. Detumescence usually follows ejaculation, but it can occur prematurely if the sex act is interrupted by an intrusive thought or event. In either case, detumescence occurs when the penile arteries narrow and the veins widen, draining blood away from the organ.
The final stage in the sex act is the quietest. It's the refractory period, a span of 30 minutes (in younger men) to three hours (in older men) during which the penis cannot respond to sexual stimulation.
For many men, sexuality is one of the things that change over time. It's usually a gradual, almost imperceptible process that begins in middle age. Whereas most older men retain an interest in sex, it's generally a far cry from the preoccupation with sex that's so common in youth. Although interest is retained, desire tends to wane; many older men think about sex, but don't have the drive to put theory into practice. And even when the spirit is willing, the flesh may be weak; male sexual performance typically declines more rapidly than either interest or desire.
Most men experience decreased sexual responsiveness with increasing age. Erections occur more slowly, and they become more dependent on physical stimulation than on erotic thoughts. Even when erections develop, most men in their 60s report that their penile rigidity is diminished and harder to sustain. The ejaculatory phase also changes with age; the muscular contractions of orgasm are less intense, ejaculation is slower and less urgent, and semen volume declines. Sperm counts also decline; although healthy men can father children well into their senior years, their reproductive efficiency can't match younger men's.
Sexual intercourse requires a partner. But male sexuality demonstrates age-related changes that are not dependent on interpersonal factors. Nighttime erections, which are normal events that occur during deep sleep, diminish with age; men between age 45 and 54 average 3.3 erections per night; between age 65 and 75, men average 2.3. Nocturnal erections also tend to become briefer and less rigid as men age.
Changes Due to Age
Sexuality is complex, and scientists don't understand all the factors that contribute to sexual function in young men, let alone what is responsible for the changes that occur with healthy aging. Still, it's clear that the hormones, nerves, and blood vessels responsible for male sexuality all change over time. In the average man, levels of testosterone fall by about 1% per year beyond age 40 - but most older men still have enough testosterone to function sexually. To produce arousal, testosterone acts on part of the brain called the locus ceruleus, and these nerve cells become less hormone-responsive with age. Levels of estradiol, a predominantly female hormone, tend to decline with age; levels of another female hormone, prolactin, tend to rise. As for nerve function, penile responsiveness to sensory stimulation also slows with age. In addition, penile blood flow may decrease as men grow older, even if they stay healthy.
Changes Due to Illness