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  3. Sleep Sleep is one of those funny things about being a human being -- you just have’ to do it. Have you ever wondered why? A

Sleep Sleep is one of those funny things about being a human being -- you just have’ to do it. Have you ever wondered why? A

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问题                           Sleep
    Sleep is one of those funny things about being a human being -- you just have’ to do it. Have you ever wondered why? And what about the crazy dreams, like the one where a bad per son is chasing you and you can’t run or yell. Does that make any sense?
Characteristics of Sleep
    When we see someone sleeping, we recognize the following characteristics:
    If possible, the person will lie down to go to sleep.
    The person’s eyes are closed.
    The person doesn’t hear anything unless it is a loud noise.
    The person breathes in a slow, rhythmic pattern.
    The person’s muscles are completely relaxed. If sitting up, the person may fall out of his or her chair as sleep deepens.
    During sleep, the person occasionally rolls over or rearranges his or her body. This happens approximately once or twice an hour. This may be ,the body’s way of making sure that no part of the body or skin has its circulation cut off for too long a period of time.
    In addition to these outward signs, the heart slows down and the brain does some pretty funky things.
    In other words, a sleeping person is unconscious to most things happening in the environment. The biggest difference between someone who is asleep and someone who has fainted or gone into a coma is the fact that a sleeping person can be aroused if the stimulus is strong enough. If you shake the person, yell loudly or flash a bright light, a sleeping person will wake up.
Who Sleeps?
    Reptiles(爬行动物), birds and mammals(哺乳动物)all sleep. That is, they become unconscious to their surroundings for periods of time. Some fish and amphibians reduce their aware ness but do not ever become unconscious like the higher vertebrates do. Insects do not appear to sleep, although they may become inactive in daylight or darkness.
    By studying brainwaves, it is known that reptiles do not dream. Birds dream a little. Mammals all dream’ during sleep.
    Different animals sleep in different ways. Some animals, like humans, prefer to sleep in one long session. Other animals like to sleep in many short bursts. Some Sleep at night, while others sleep during the day.
Sleep and the Brain
    If you attach an electroencephalograph to a person’s head, you can record the person’s brainwave activity. An awake and relaxed person generates alpha waves, which are consistent oscillations at about 10 cycles per second. An alert person generates beta waves, which are a bout twice as fast.
    During sleep, two slower patterns called theta waves and delta waves take over. Theta waves have oscillations in the range of 3.5 to 7 cycles per second, and delta waves have oscillations of less than 3. 5 cycles per second. As a person falls asleep and sleep deepens, the brain wave patterns slow down. A person deep in delta wave sleep is hardest to wake up.
REM Sleep
    At several points during the night, something unexpected happens -- rapid eye movement(REM)sleep occurs. Most people experience three to five intervals of REM sleep per night, and brainwaves during this period speed up to awake levels. If you ever watch a person or a dog experiencing REM sleep, you will see their eyes flickering back and forth rapidly. In many dogs and some people, arms, legs and facial muscles will twitch during REM sleep. Periods of sleep other than REM sleep are known as NREM(non-REM)sleep.
    REM sleep is when you dream. If you wake up a person during REM sleep, the person can vividly recall dreams. If you wake up a person during NREM sleep, generally the person .will not be dreaming.
    You must have both REM and NREM sleep to get a good night’s sleep. A normal person will spend about 25 percent of the night in REM sleep, and the rest in NREM. A REM session -- a dream -- lasts five to 30 minutes.
When You Miss Some Zzzzs...
    One way to understand why we sleep is to look at what happens when we don’t get enough:
    As you know if you have ever pulled an all-nighter, missing one night of sleep is not fatal. A person will generally be irritable during the next day and will either slow down(become tired easily)or will be totally wired because of adrenalin(肾上腺素).
    If a person misses two nights of sleep, it gets worse. Concentration is difficult, and attention span falls by the wayside. Mistakes increase.
    After three days, a person will start to hallucinate and clear thinking is impossible. With continued wakefulness a person can lose grasp of reality:’ Rats forced to stay awake continuously will eventually die, .proving that sleep is essential.
    A person who gets just a few hours of sleep per night can experience many of the same problems over time.
    Two other things are known to happen during sleep. Growth hormone in children is secreted during sleep, and chemicals important to the immune system are secreted during sleep. You can become more prone to disease if you don’t get enough sleep, and a child’s growth can be stunted(阴碍)by sleep deprivation.
Why Sleep?
    No one really knows why we sleep. But, there are all kinds of theories, including these:
    Sleep gives the body a chance to repair muscles and other tissues, replace aging or dead cells, etc.
    Sleep gives the brain a chance to organize and archive memories. Dreams are thought by some to be part of this process.
    Sleep lowers our energy consumption, so we need three meals a day rather than four or five. Since we can’t do anything in the dark anyway, we might as well "turn off" and save the energy.
    What we all know is that, with a good night’s sleep, everything looks and feels better in the morning. Both the brain and the body are refreshed and ready for a new day.
Dreams
    The brain creates dreams through random electrical activity. Random is the key word here. About every 90 minutes the brain stem sends electrical impulses throughout the brain, in no particular order or fashion. The analytic portion of the brain -- the forebrain -- then desperately tries to make sense of these Signals. It is like looking at a Rorschach test, a random splash, of ink on paper. The only way of comprehending it is by viewing the dream(or the inkblot)metaphorically, symbolically, since there’s no literal message.
    This doesn’t mean that dreams are meaningless or should be ignored. How our forebrains choose to "analyze" the random and discontinuous images may tell us something about our selves, just as what we see in an inkblot can be revelatory. And perhaps there is a purpose to the craziness: Our minds may be working on deep-seated problems through these circuitous and less threatening metaphorical dreams.
    Here are some other things you may have noticed about your dreams:
    Dreams tell a story. They are like a TV show, with scenes, characters and props.
    Dreams are egocentric. They almost always involve you.
    Dreams incorporate things that have happened to you recently. They can also incorporate deep wishes and fears.
    A noise in the environment is often worked in to a dream in some way, giving some credibility to the idea that dreams are simply the brain’s response to random impulses.
    You usually cannot control a dream -- in fact, many dreams emphasize your lack of control by making it impossible to run or yell.
    Dreaming is important. In sleep experiments, where a person is woken up every time he/she enters REM sleep, the person becomes increasingly impatient and uncomfortable over time.
How Much Sleep Do I Need?
    Most adult people seem to need seven to nine hours of sleep a night. This is an average, and it is also subjective. You, for example, probably know how much sleep you need in an average night to feel your best.
    The amount of sleep you need decreases with age. A newborn baby might sleep 20 hours a day. By age four, the average is 12 hours a day. By age 10, the average falls to 10 hours a day. Senior citizens can often get by with six or seven hours a day.
The brain stem sends electrical impulses throughout the brain about every ______.
选项
答案90 minutes
解析 根据题干The brain stem sends electrical impulses throughout the brain about every…可推测本题需填表频率的数字，迅速将查找内容定位在About every 90 minutes the brain stem sends electrical im pulses throughout the brain，in no particular order or fashion处。这样，答案就显而易见了。一般出题的顺序与查找内容在原文的顺序是一
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