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What is Sleep?
Sleep is a resting state, both physical and mental, when a person becomes relatively inactive and unaware of their environment. Basically, at sleep, a person is partially detached from the world and most external factors are blocked from the senses.
During normal sleep, there will usually be a general decrease in body temperature, blood pressure, breathing rate and most other bodily functions. The human brain, however, never decreases inactivity. The brain has been shown to be as active during sleep as it is when awake. During an eight-hour sleep cycle, a normal adult alternates between two very different states, non-REM and REM (Rapid Eye Movement) sleep.
Sleep Cycles – what are they?
Sleep is characterized by two distinct states, non-REM sleep and REM sleep. Non-REM and REM sleep alternate in 90- to 110-minute cycles. A normal sleep pattern has 4-5 cycles.
The five-step sleep cycle repeats itself throughout a night of sleeping, a little like a roller coaster. When a person drifts off to sleep, Stage 1 begins. After a few minutes, the EEG detects sleep. It may take anywhere from 30 – 40 minutes to cycle through Stage 2 through 4. Now, an individual backtracks through Stage 3, then Stage 2, and finally into REM sleep. This occurs 4 - 5 times per night.
NON REM Sleep
Non-REM sleep occurs in four stages that range from light dozing to deep sleep. Throughout this state of sleep, muscles are still functioning, breathing has slowed considerably and brain activity is minimal. Approximately 75% of the sleep cycle is spent in non-REM sleep. Simple thought processes may be reported if a person is awakened in any stage of non-REM sleep; however, he or she will not usually remember specific dreams.
Wakefulness - This is a state of awareness in which an individual is conscious of his or her surrounding environment and is able to interact with it. In the period before sleep, wakefulness is described as quiet wakefulness, where the individual is resting in a relaxed condition with his or her eyes closed. This stage is characterized by alpha and beta waves activity.
What Determines When We Sleep?
One of the main reasons why people sleep is the circadian rhythms, also known as the biological clock. A CIRCADIANA cycle lasts 24 hours. Some functions that are called circadian include body temperature and certain hormone secretions. So too, humans have a natural cycle of approximately the length of one day.
Small structures in the brain regulate circadian rhythms. Sleep and wakefulness alternate, usually between night and day, respectively. For most people, sleepy peaks occur every 12 hours, at night, and around mid-afternoon. Through a complex process of hormonal and neurological changes, daylight naturally triggers periods of wakefulness.
The greater time a person remains awake, the more sleep he or she requires; therefore, the need to sleep grows throughout periods of wakefulness.
Normal peaks of alertness occur during daylight hours. The mid-afternoon dip, called a postprandial dip (after lunch), is caused by a natural decrease in body temperature. When our body temperature begins to drop, we are sleepier than when it begins to rise.
Why Do We Need Sleep?
Some believe that sleep is a waste of time. This is not the case. Sleep is vital for a number of theoretical reasons:
It is restorative – it enables the body and mind to rejuvenate, reenergize, and restore. When a person sleeps, it is thought that the brain performs vital housekeeping tasks, such as organizing long-term memory, integrating new information, and repairing and renewing tissue, nerve cells and other biochemical's. Sleep allows the body to rest and the mind to sort out past, present, and future activities and feelings.
Adaptive - Sleep may have evolved as a protective adaptation-finding food in the daytime and hiding at night is easier. Nearly every animal sleeps to some degree. Therefore, it makes sense that predators sleep more than animals that are prey. For humans, the amount and quality of sleep achieved is directly proportional to the amount and quality of the next day's productivity.
What are the Consequences of Sleep Depravation?
Current lifestyles mean that today's society is often sleep deprived. People need to understand how prevalent sleep deprivation is.
It is estimated that nearly 50% of the adult population is sleep deprived. This may be because of longer work hours and increased commute times. It could be argues that the price of the boost in productivity is a reduction in sleep.
So, what is happening to all of these exhausted individuals? Many tragedies that have been linked to human error were due to exhaustion. Some historic examples of severe sleep deprivation include the Exxon Valdez oil spill, the NASA Challenger shuttle explosion, and the Chernobyl nuclear accident. Unfortunately, accidents can easily happen as the result of any amount of lost sleep.
The most common consequence of lost sleep has become a public health issue - sleeping behind the wheel. One third of all drivers will fall asleep while driving at least once in their lifetime. The monetary cost is estimated at more than $30 billion annually and the human cost is roughly 100,000 crashes, 71,000 injuries, and 1,500 fatalities each year. These figures are probably very conservative due to inaccurate statistics. Moreover, this estimate does not account for other operators "behind a wheel", such as airline pilots, boat captains, and railway conductors.
How Much Sleep Do We Need?
Research indicates that the average person requires six to eight hours sleep per day. That's about one-third of a lifetime! As a population, we sleep about 1 to 1.5 hours less than we did 100 years ago.
Sleep requirements vary from person to person-some people are naturally short or long sleepers. Some experts suggest that the best way to determine personal sleep requirements is by waking up without an alarm clock. The amount of time spent sleeping would be the personal requirement. Other experts suggest that an ideal amount of sleep is the amount needed to feel refreshed and well rested in the morning and alert all day.
Contrary to popular belief, the amount of sleep a person needs does not decrease with age. The reality is that sleep patterns and circadian rhythms change as one ages. Infants spend 50% of their sleep time in non-REM sleep and 50% in REM sleep; it has been shown that deep sleep coincides with the release of growth hormones, necessary for growing children. Adults spend approximately 20% in REM sleep, while elderly people may spend only 15% in REM sleep. Older adults tend to spend most of their sleep time in Stage 1 of non-REM sleep. Consequently, they have less REM sleep and report frequent awakenings
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