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3.4 Sleep patterns. Sleep patterns change during an individual’s life. In fact, age affects sleep more than any other natural factor. Newborns sleep an average of 16 to 18 hours per day. By the time a child is three to five years old, total sleep time averages 10 to 12 hours, and then it further decreases to 7 to 8 hours per night by adulthood. One of the most prominent age-related changes in sleep is a reduction in the time spent in the deepest stages of NREM (Stages 3 and 4) from childhood through adulthood. In fact, this change is prominent during adolescence, when about 40 percent of this activity is lost and replaced by Stage 2 NREM sleep. In addition to these changes, the percentage of time spent in REM sleep also changes during development. Newborns may spend about 50 percent of their total sleep time in REM sleep. In fact, unlike older children and adults, infants fall asleep directly into REM sleep. Infant sleep cycles generally last only 50 to 60 minutes. By two years of age, REM sleep accounts for 20 to 25 percent of total sleep time, which remains relatively constant throughout the remainder of life. 15 Young children have a high arousal threshold, which means they can sleep through loud noises, especially in the early part of the night. For example, one study showed that 10-year-olds were undisturbed by a noise as loud as the sound of a jet airplane taking off nearby. Although most humans maintain REM sleep throughout life, brain disorders like Alzheimer’s and Parkinson’s are characterized by decreasing amounts of REM sleep as the diseases progress. Also, elderly individuals exhibit more variation in the duration and quality of sleep than do younger adults. Elderly people may also exhibit increased sleep fragmentation (arousals from sleep that occur as either short or more extended awakenings). Figure 6 depicts these developmental changes in sleep patterns. Teenagers, on average, require about nine or more hours of sleep per night to be as alert as possible when awake. Several issues are important to consider. First, individual sleep needs vary. For instance, eight hours of sleep per night appears to be optimal for most adults, although some may need more or less. Teenagers, on average, require about nine or more hours of sleep per night to be as alert as possible when awake. If sleep needs are not met, a Figure 6. Average sleep need (left graph) and percentage of REM sleep (right graph) at different ages. 25 Information about Sleep
Sleep, Sleep Disorders, and Biological Rhythms Biological rhythms are of two general types. Exogenous rhythms are directly produced by an external influence, such as an environmental cue. They are not generated internally by the organism itself, and if the environmental cues are removed, the rhythm ceases. Endogenous rhythms, by contrast, are driven by an internal, self-sustaining bioprogressive sleep debt occurs and eventually the body requires that the debt be paid. It does not appear that we are able to adapt to getting less sleep than our bodies require. Not getting enough sleep, while still allowing us to function in a seemingly normal manner, does impair motor and cognitive functions. Caffeine and other stimulants cannot substitute for sleep, but they do help to counteract some of the effects of sleep deprivation. 3.5 Biological clock. An internal biological clock regulates the timing for sleep in humans. The activity of this clock makes us sleepy at night and awake during the day. Our clock cycles with an approximately 24-hour period and is called a circadian clock (from the Latin roots circa = about and diem = day). In humans, this clock is located in the suprachiasmatic nucleus (SCN) of the hypothalamus in the brain (see Figure 7). 21 The SCN is actually a very small structure consisting of a pair of pinhead-size regions, each containing only about 10,000 neurons out of the brain’s estimated 100 billion neurons. Biological clocks are genetically programmed physiological systems that allow organisms to live in harmony with natural rhythms, such as day/night cycles and the changing of seasons. The most important function of a biological clock is to regulate overt biological rhythms like the sleep/wake cycle. The biological clock is also involved in controlling seasonal reproductive cycles in some animals through its ability to track information about the changing lengths of daylight and darkness during a year. Figure 7. The biological clock is located within the suprachiasmatic nucleus in the brain. 26
Page 1 and 2: Sleep, Sleep Disorders, and Biologi
Page 3 and 4: BSCS Development Team Rodger Bybee,
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Page 8: About the National Institutes of He
Page 12 and 13: Introduction to Sleep, Sleep Disord
Page 14 and 15: Implementing the Module The six les
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Sleep, Sleep Disorders, and Biologi
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Sleep Medicine Reference Manual SLE
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Sleepiness Scale Graph Template Nam
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Evaluating Sleep Disorders Lesson 4
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Key aspects of case studies and ans
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3. How would you suggest that this
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Snoring—Believe It or Not! A burg
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Sleep Disorders Reference Manual In
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Reconvene the class and have each s
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Newspaper Articles The Gotham Daily
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Appendix III More About the Nationa
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