A Common Action: sleeping
Abstract:月季种子 Understanding the prominent role of sleep in life and learning exactly why people need sleep are topics of much debate and speculation among sleep scientists. Recent animal studies have suggested that sleep is necessary for survival. Sleep appears necessary for our nervous systems to work properly. Too little sleep leaves us drowsy and unable to concentrate the next day. It also leads to impaired memory and physical performance and reduced ability to carry out math calculations. Without sleep, neurons may become so depleted in energy or so polluted with byproducts of normal cellular activities that they begin to malfunction. Sleep may also give the brain a chance to exerci important neuronal connections that might otherwi deteriorate from lack of activity.
Key words: sleep, nervous system, insomnia,
1 What are the stages of sleep?
During sleep, we usually pass through five phas of sleep: stages 1, 2, 3, 4, and REM (rap
修理的英文id eye movement) sleep. The stages progress in a cycle from stages 1 to 4 to REM sleep, then the cycle starts over again with stage 1. We spend almost 50 percent of our total sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages.
During stage 1, which is light sleep, we drift in and out of sleep and can be awakened easily. Our eyes move very slowly and muscle activity decreas.
When we enter stage 2 sleep, our eye movements stop and our brain waves become slower, with occasional bursts of rapid waves.
In stage 3, slow brain waves called delta waves begin to appear, intersperd with smaller, faster waves.
By stage 4, the brain produces delta waves almost exclusively. It is more difficult to wake someone from stages 3 and 4, which together are called deep sleep, than from other stages of sleep. There is little or no eye movement or muscle activity. People awakened fr
老顽童图片om deep sleep do not adjust immediately and often feel groggy and disoriented for veral minutes after they wake up.
When we switch into REM sleep, our breathing becomes more rapid, irregular, and shallow, our eyes jerk rapidly in various directions, and our limb muscles become temporarily paralyzed. Our heart rate increas and our blood pressure ris. When people awaken during REM sleep, they often describe bizarre and illogical tales dreams.
The first REM sleep period usually occurs about 70 to 90 minutes after we fall asleep. The first sleep cycles of each night contain relatively short REM periods and long periods of deep sleep. As the night progress, REM sleep periods increa in length while deep sleep decreas. By morning, people spend nearly all their sleep time in stages 1, 2, and REM.
2 How much sleep do we need?
For most adults, 7 to 8 hours a night appears to be an appropriate amount of sleep, altho
ugh some people may need as few as 5 hours or as many as 10 hours of sleep each day. Older people generally need about the same amount of sleep as they needed in early adulthood. The amount of sleep a person needs increas temporarily if he or she has been deprived of sleep in previous days. Getting too little sleep creates a "sleep debt," which is much like being overdrawn at a bank. Eventually, your body will demand that the debt be repaid. Sleep need returns to normal when the sleep debt is repaid. We don't em to adapt to getting less sleep than we need. Although we may get ud to a sleep-depriving schedule, our judgment, reaction time, and other functions are still impaired.
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Experts say that if you feel drowsy during the day, even during boring activities, you haven't had enough sleep. If you routinely fall asleep within 5 minutes of lying down, you probably suffer from sleep deprivation, possibly even a sleep disorder. Microsleeps, or very brief episodes of sleep in an otherwi awake person, are another mark of sleep deprivation. In many cas, people are not aware that they are experiencing microsleeps.
3 How does sleep change as we age?ppt转图片
Many older people do not enjoy a good night's sleep on a regular basis. People tend to sleep more lightly and for shorter periods as they get older. About half of all people over 65 frequently experience sleeping disorders, such as insomnia, defined as difficulty falling or staying asleep. By age 75, some people may find they are waking up veral times each night. Nighttime sleeping problems can result in excessive daytime sleepiness, attention and memory problems, depresd mood, and lowered quality of life.什么是社会问题
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