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That wonderful world of sleep has four distinct stages that make up a 90-minute or so cycle that repeats severaltimes over the course of the night. These stages include:

Stage 1: This is the beginning of the sleep cycle and is relatively light. It can be considered a transition period between wakefulness and sleep. When you wake people during this stage, they often will swear that they were awake all along, says Dr. Rachel Morehouse, Medical Director, Atlantic Sleep Centre, St. John Regional Hospital, New Brunswick.

Stage 2: During this stage, the brain begins to emit bursts of rapid, rhythmic brain wave activity, indicating alternating periods of muscle tone and muscle relaxation. The heart rate slows and the body temperature decreases, as the body prepares to enter deeper sleep. During this stage, people are unaware of what’s going on around them. “It’s OK sleep but not great sleep; it’s not that restorative,” says Morehouse.

Stage 3: As your body moves into deep sleep, you begin to emit slower brain waves known as delta waves. It’s during this deep stage of sleep that your body repairs and regenerates tissues, builds bone and muscle, and probably strengthen the immune system. It’s also during this deep sleep that bed-wetting and sleep-walking are more likely to occur. “It’s harder to wake someone out of this stage; people are definitely not aware of what’s going on around them,” says Morehouse. “It’s the most restorative type of sleep; the type of sleep babies get a lot of and seniors get almost none of.”

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Stage 4: This stage is referred to as rapid eye movement (REM) (the first stages are called non-REM) which is characterized by very active brain wave patterns. It’s during REM that people typically have dreams, especially vivid ones. “This stage is totally unique, fascinating and amazing” but not all that restorative, says Morehouse. Some researchers believe that we use this stage to record what happened during waking hours. “We file these things away in our brain in a place we can find them later,” she says. Think you don’t ever dream? That may be because you wake up during a non-REM stage. If you wake up directly from REM, chances are you’ll remember what you were dreaming. During the night, we generally cycle between the various stages, with the 3 non-REM sleep stages occurring in the early part of the night and the REM coming in blocks that typically get longer over the course of your sleep, according to Dr. Maureen Ceresney, a Sleep Specialist at the University of British Columbia, Vancouver. The exact functions of the different stages are a topic of ongoing research, she says. Melatonin, the hormone produced in the pineal gland in the brain, helps to regulate the sleep cycle. While all cells in the body have a daily (‘circadian’) clock rhythm, the pineal gland is considered the “master clock”, says Ceresney. “Light reaching the light sensitive cells at the back of the eyes creates a signal that is transmitted along nerve cells travelling in the brain to turn off the release of melatonin from the pineal gland. As the eyes begin to perceive darkness, the release of melatonin is no longer inhibited.” People with a well-regulated sleep-wake schedule have a fairly predictable, rhythmic release of melatonin that begins in the evening, in the few hours before their normal bedtime and peaks later in the night, says Ceresney. As you get older, you sleep more lightly and get less deep sleep. Aging is also associated with shorter time spans of sleep, although studies show the amount of sleep needed doesn’t appear to diminish with age. Women of all ages appear to be more prone to sleep problems, likely because of rapid spikes and drops in hormone levels associated with monthly menstrual cycles, pregnancy and menopause. Hot flashes – those annoying rushes in body temperature that women experience in the months leading up to, and during, menopause – are notorious for disturbing sleep for older women.

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