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The nature of sleep and the role it plays in our lives has long fascinated science and been the focus of many studies and a grea

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问题     The nature of sleep and the role it plays in our lives has long fascinated science and been the focus of many studies and a great deal of research.
    A. The benefit of receiving enough sleep is essential to our inner well-being. Not enough sleep, however, means that we lack the opportunity to restore ourselves physiologically, emotionally and cognitively. It affects our mood and can result in behaviour and performance problems. When we sleep, our bodies rest but our brains are active. Sleep lays the groundwork for a productive day ahead. Although most people benefit the most from eight hours of sleep each night, this is not always what they manage to achieve. Men get slightly less sleep than women during the week (6.7 hours/night vs. 7.0 hours /night), but have fewer sleep problems, according to recent Sleep in America polls conducted annually by the National Sleep Foundation (NSF).
    B. According to current scientific thought, the human body is pre-programmed for sleep. At nightfall, cells in the retina (a light sensitive membrane connected to the eye by the optic nerve) send a sleep signal to a cluster of nerve cells in the brain. These nerve cells are concentrated together in the suprachiasmatic nucleus (SCN) and are located in a part of the brain called the hypothalamus which helps regulate body temperature. The SCN is also known as the circadian clock. This biological "clock" relays the message to other parts of the brain which then signals the body that it is time to sleep. For instance, the pineal gland, also located in the hypothalamus, produces a substance called melatonin, which lowers body temperature, and causes drowsiness.
    C. A great deal of the information we now know about sleep and the physiological changes it causes in the brain can be traced back to the invention of the electroencephalogram in the 1950s. This machine allowed scientists to record the feeble electric currents generated on the brain without opening the skull and to depict them graphically onto a strip of paper. Brain-wave function could be examined and scientists could thereby observe sleep from moment to moment. In the 1970s it became possible for scientists to make assumptions about the role that correct breathing plays during sleep with the development of the technology to measure respiration. It was here that science really began to understand the nature of sleep and the role it plays in people’s lives.
    D. As well as uncovering the physiological changes occurring during sleep, The New England Journal of Medicine reported that sleep concerns were a public health threat as serious as smoking and in the years since, medical researchers have linked sleep disorders with many life-threatening diseases. Even though more than 70 million Americans have a sleeping problem, most cases go undiagnosed and untreated, so the true economic and sociological damage caused by these disorders is unknown although, the economic cost is conservatively estimated to be billions of dollars a year in healthcare costs and lost productivity. Breathing problems during sleep represent by far the greatest proportion of sleep disorders and cause the most concern, with studies showing that between 50% and 80% of stroke and heart failure patients have breathing problems during sleep.
    E. Scientific studies have found that children who are identified as snorers or those who have poor sleeping patterns at around the age of four or five, scored lower than average in Intelligence Quotient (IQ) tests, not only during the sleep deprivation period but subsequent to that. There are also suggestions that ongoing sleep deprivation in adults can cause permanent damage.
    F. Teenagers can have peculiar sleep requirements. It has always been known that adolescents spend more time sleeping than adults, but science has only recently isolated the reasons for this. Research now shows that growth hormones are secreted during slow-wave sleep and teenagers do indeed, need more of this kind of sleep than at any other stage in their lives. Chronic lack of sleep among teenagers means that as a group they are more likely to use stimulants and experience negative mood swings. Statistics also indicate that young drivers are responsible for more than one-half of fall- asleep crashes.
    G. However, it is not just young people who pay the price for lack of proper sleep. Workers are robbing themselves of sleep in order to increase productivity in both their social and working lives. In recent years, however, the identification of driver fatigue as the possible cause of 1/3 of all accidents provides some indication of the price we are paying for such a trade-off. Extensive scientific research indicates that chronic tiredness has been the cause of environmental disasters, nuclear mishaps and several well-documented near misses in the air. Scientists are beginning to argue that the lengthening of the working day is harming workers, their families and society. In the long run, productivity will suffer.
    H. As a reaction against this disturbing trend, there has been increased support for regulation of the number of hours worked by employees in demanding jobs, such as doctors, nurses, pilots, bus drivers and truck drivers. Legislation is being drafted to limit work hours, thus forcing companies to become instrumental in changing work cultures to ensure employees are getting enough rest and leisure time in order to avoid chronic tiredness and its devastating consequences.
Companies have to be more active in preventing accidents caused by human factors. ______
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