考研优美英语作文的背诵049
</p><p> <span word="Sleep">Sleep</span></p><p> <span word="Sleep">Sleep</span> is part of a persons daily activity cycle. There are severaldifferent stages of sleep, and they too occur in cycles. If you are anaverage sleeper, your sleep cycle is as follows. When you first drift off intoslumber, your eyes will roll about a bit, your temperature will dropslightly, your muscles will relax, and your breathing well slow andbecome quite regular. Your brain waves slow down a bit too, with thealpha rhythm of rather fast waves predominating for the first few minutes.This is called stage 1 sleep. For the next half hour or so, as you relaxmore and more, you will drift down through stage 2 and stage 3 sleep. The loweryour stage of sleep, the slower your brain waves will be. Then about 40 to 60minutes after you lose consciousness you will have reached the deepest sleep ofall. Your brain waves will show the large slow waves that are known as the deltarhythm. This is stage 4 sleep.You do not remain at this deep fourth stageall night long, but instead about 80 minutes after you fall into slumber,your brain activity level will increase again slightly. The delta rhythm willdisappear, to be replaced by the activity pattern of brainwaves. Your eyes will begin to dart around under your closed eyelids asif you were looking at something occurring in front of you. This period ofrapid eye movement lasts for some 8 to 15 minutes and is called REM sleep.It is during REM sleep period, your body will soon relax again, your breathingwill grow slow and regular once more, and you will slip gently back fromstage 1 to stage 4 sleep - only to rise once again to the surface of nearconsciousness some 80 minutes later.</p>
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