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Sleep: What Is It? Why Do We Need It? and How Much Is Enough?

Sarah Mellors's picture

All human beings – old, young, sick, healthy – need sleep.  Thus, everyone should have an interest in this natural phenomenon.  However, most people never question what sleep is and why they must get it.  At the ripe age of 18 years, I thought it was high time I understand why I am always craving sleep and why I feel noticeably better when I get a certain amount of it.  This paper will explore what goes on in our bodies when we’re in this ambiguous state called “sleep”, why it is necessary to function, and how much we should be getting.

What is sleep?  Sleep is characterized by a number of things: a reduction in voluntary movement, decreased reaction to external stimuli, an increased rate of anabolism (synthesizing cell structures), a decreased rate of catabolism (breaking down cell structures), a stereotypic posture (lying down), and reversibility (we can wake from sleep) (3).  Sleep can be broken down into two kinds: REM, Rapid Eye Movement, which accounts for 20-25% of sleep, and NREM, non-REM, which constitutes 75-80% of sleep. Interestingly, sleep is cyclical and occurs in 90-minute phases of REM and NREM; on a given night, a person may have between 3 and 6 NREM-REM cycles.  Non-REM sleep consists of four stages of brain activity: stage 1 is the “gateway stage between wake and sleep” where theta brain waves of sleep replace alpha waves of wakefulness, in stage 2 is characterized by sleep spindles and K-complexes and awareness of the environment disappears, stage 3 is characterized by delta brain waves, and stage 4 is true deep sleep (“this is the stage where night terrors, bed wetting, and sleepwalking occur”).  REM sleep is best known that period where we dream (1).  It is interesting to note that the period where we dream is the shortest part of the whole sleep cycle, yet it is the only part we remember in the morning. 

Now that we have a more thorough understanding of what is known about the physiology of sleep, we can explore why sleep is so important and what happens when we do not get enough.  From my research, it has become apparent that while much is known about the brain activity that occurs during sleep, little has been discovered about why we need sleep for survival (3). 

An interesting study I came across discussed the effects of sleep deprivation on rats.  Rats normally live 3-4 years, but those deprived of REM sleep only lived about 5 weeks, and those deprived of all sleep only lived for 3 weeks.  Curiously, the sleep-deprived rats experienced abnormally low body temperature and developed sores on their tails and paws.  This study exemplifies the theory that sleep has restorative properties and may be necessary for the immune system to function, which explains why sores appeared on the rats’ bodies when they did not get enough sleep (3).

Visible signs in everyday life reveal other effects of sleep-deprivation.  Without sleep, we experience drowsiness and difficulty concentrating.  Studies show that people who are sleep-deprived have more trouble performing math calculations, have impaired physical performance, and have more difficulty retaining information.  Many theories exist about the relationship between memory and sleep, but no conclusive data has been found.  Some evidence shows that sleep improves short-term memory; however, scientists so far have not determined if a connection exists between sleep and long-term memory.  Further experimentation with memory and sleep could elucidate this obscure area (1).

Clearly getting enough sleep is crucial, but how much sleep is enough?  According to common knowledge, everyone should get eight hours of sleep a night, but research shows that because of diversity of age and genetic makeup different people need different amounts of sleep.  How much sleep a person needs depends on several factors: inherited genetic need, “sleep hygiene” (controlled activities such as drinking alcohol or coffee, smoking, and exercise), quality of sleep, and circadian rhythm, which is the 24-hour cycle of physiological cycle that exists in all living things (2).  Data reveals that sleep is necessary for growth and proper metabolism; children between the ages of 3 and 5 should be getting 11-13 hours of sleep a night for optimal growth and development.  The National Sleep Foundation maintains that adults need between 7 and 8 hours of sleep a night, but this varies from person to person (1).  People who do not get enough sleep over a long period of time develop a “sleep debt”, which consists of the number of hours of sleep they should have gotten but didn’t get and will need to make up sometime in the future (2). 

After much research and thought, I have concluded that although many studies have been done concerning sleep, much is still yet to be discovered and nothing is ever certain.  Furthermore, genetic diversity and individual characteristics are variables that complicate the quest for conclusive information; what applies to one person may not apply to everyone.  Thus, it is difficult to determine how much sleep each person needs.  However, some consistent general observations have been made, such as: small children need more sleep than adults and sleep is essential for survival, optimal performance, growth, and concentration.  More conclusive data has been obtained about how the brain functions during sleep, but scientists are still unsure exactly why sleep is necessary.

Having researched and written this paper, I now know why I feel so much more aware and able to concentrate after a good night’s sleep.  I am sure everyone in this class can relate and now you know the current story scientists have developed to explain this phenomenon.  Knowing that sleep enhances thought processes and healing power, perhaps I will take this into account when preparing for an exam or when trying to recover from a cold.

World Wide Web Sources

1) A very thorough Wikipedia article on sleep

2 An informative article from the WebMd webpage entitled, “How Much Sleep Do You Really Need?”

3) Part of the University of Wisconsin School of Medicine and Public Health School of Medicine’s Webpage about the science of sleep.




someone you'll never meet's picture

Time Limit

Is there a certain amount of time where people start to die when lacking sleep? One time I was staying up with a friend, and eventually at 3:00 we realized that we hadn't fallen asleep. His mother was going to pick him up around 10:00, and I had a meeting with one of my friends that would last all day. When I was with her, I felt less tired. Also, for some strange reason, I did things alot better whan I was tired. I played guitar hero alot better, especially in the hard solo riffs. So basically, sleep made me more alert. Is this normal? Will it be posssible for me to stay awake for long periods of time without rest? What is the most someone has gone without sleep? Death or life in the case does not matter.

guest bob's picture

Re:Time limit

i have heard that people have stayed up for a week at a time before but they've all been admitted to hospital because of it i would recommend not staying up to see how long you stay awake its very dangerous

Anonymous's picture

I know this comment was

I know this comment was written a very long time ago but hopefully you will still read this message and find it helpful. It is normal for some people to feel more alert when they are tired. However, what these people feel is only a misperception of how they really feel due to lack of sleep. There was a study done where sleep deprived people and non-sleep deprived people took a certain test. After taking the test, they were asked how concentrated they felt during the exam and were asked how concentrated they felt. The non-sleep deprived people felt their performance was averaged to be a 3 out of 5 and concentration averaged out to 3.5 out of 5. Interestingly, those who were sleep deprived on average claimed to have a performance of 4 out of 5 and 4.5 out of five for alertness and concentration. However, the non-deprived students actually performed better than did the deprived. This shows that tiredness can trick some into believing that they are more alert while in actuality, their performance is not at all at their best. It is not possible for someone to actually be more alert while sleep deprived. Its biologically impossible.

Anonymous's picture

Thank you for the useful information.

Thanks, that helps a lot! You're right, that was a while ago, and I totally forgot I wrote that, but it's exciting to hear a response. Thanks again.

Amanda's picture


I'm looking for a piece that was done on 20/20 or dateline or something along those lines where a man died because he lacked REM, basically he never dreamed. I was wondering if anyone has more information on this or knows anything about the piece done on this.