The Hormonal Sleep Cycle
Written by clive on 11:28 PMLight that reaches photoreceptors in the retina (a tissue at the back of the eye) creates signals that travel along the optic nerve to the SCN. Then, signals from the SCN travel to several brain regions, including the pineal gland, which responds to these light-induced signals by switching off production of the hormone melatonin. This is what wakes us up.
As the day progresses, and light fades, the pineal gland receives a signal to increase production of the hormone melatonin, getting us ready for bed. This complex arrangement of light and melatonin may be one reason we tend to be sleepier in the winter: As the number of daylight hours decreases and the brain secretes more melatonin, it's harder to wake up in the morning, and midafternoon naps become more tempting.
The melatonin/light relationship is the reason why many totally blind people experience lifelong sleeping problems. Because their retinas are unable to detect light, their circadain rhythms follow their innate - 25-hours - cycle rather than a 24-hour one, leading to a feeling of permanent jet lag and periodic insomnia.
Other hormones play a role in sleep beside melatonin. One of the most important is serotonin, the precursor to melatonin. Growth hormone (gH) is secreted primarily during the early phases of sleep. When we're young, gH is critical for growth; as we age, it plays an important role in repairing and regenerating tissue. Then, toward morning, as melatonin levels drop, levels of cortisol (a hormone that signals alertness) rise, peaking just when we awaken.
Female sex hormones also play a role, and may be one reason women generally have more sleep problems and more deep sleep than men, notes, Joyce Walsleben, Ph.D., director of the sleep disorders center at NYU School of Medicine and author of A Woman's Guide to Sleep (Three Rivers Press, 2000). The female hormone progesterone seems to have a sedating effect (and is highest just before women menstruate, which may explain some of the fatigue of PMS), while estrogen seems to enhance REM sleep, which may explain the unusually vivid dreams many women say they have during pregnancy, when estrogen levels are higher.
SEVEN DAYS TO A PERFECT NIGHT'S SLEEP, DEBRA L.GORDON
0 comments: Responses to “ The Hormonal Sleep Cycle ”