Sleep is defined as a regularly recurring condition of body and mind in which the nervous system is inactive. During sleep, a body will undergo five stages of sleep, of which four is NREM (Non-Rapid Eye Movement) and one is REM (Rapid Eye-Movement) [Schenck (2007 4)].

Theoretical frame

5 Stages of Sleep [(Green, Muir, James, Gradwell, & Green (1996 3)]
The five stages of sleep follow a predictable pattern of REM and NREM but the duration and proportion are not equal and are dependant on many factors. The deeper the sleep and length of time in deep sleep, the more the body and mind are getting to rest.

The stages of sleep can be determined from the patterns of Electroencephalogram (EEG) {which comprises of electrodes that are glued to the human head in a particular position}, Electrooculogram (EOG) { electrodes position to the outer layer of the human eyes region}, and Electromyogram (EMG) {which comprises of two electrodes attached to the human skin under the chin area which provides information about muscle tension or relaxation} [(Green, Muir, James, Gradwell, & Green (1996 3)]

When a person is awake, the EEG will display two patterns consisting of Alpha and Beta activities. Alpha activity is mostly observed when resting with eyes closed. Beta activity on the other hand are often aroused or takes over Alpha activity. This can happen with effects such as solving a problem or distractions of noise etc.

This is the start of the sleeping process which alpha activity recorded as small, rapid and irregular waves with EOG demostrating slow rolling eye movements. It is a transition stage between being awake and sleeping. EEG will increase as sleep progresses which contain low frequency of voltage activity also known as Delta activity [(Green, Muir, James, Gradwell, & Green (1996 3)]. A typical sleep cycle will be about 10minutes for this stage.If one was to be awake from stage one sleep, one may feel as if he or she has not slept at all. Body temperature begins to decline and the alpha waves prior to sleep begin to change to theta waves. Brief muscle contractions before sleep, known as hypnic jerks, generally occur in stage one sleep [Schenck (2007 4)].

At the second stage, this will occur for about 10 to 25 minutes with delta activity increasing. It had been stated that 50% of sleep occurs at this stage. One will be disengaged to their environment and respiration rate, heart rate, body temperature and muscle tension will decline. Stage two sleep simply meant that body is preparing to go to deep sleep.

The deeper stage of sleep in which delta activities will increase with slow waves of sleep. During deep sleep energy is regained and growth hormones are excreted while respiration rate, heart rate, body temperature and muscle tension will continue to decline. One will remain in stage four sleep on average for 30 minutes before the cycle repeats itself in a backwards fashion. Stage 3 last for an approximate period of 15minutes prior to entering Stage 4 which will last approximately 90minutes. Most of the Stage 4 sleep cycle is acomplished early in the night. Stage four is the last stage of NREM before REM occurs, when the cycle returns back to stage one, one will enter the fifth stage of sleep known as the REM [(Green, Muir, James, Gradwell, & Green (1996 3)].

This Stage is known as the Rapid Eye Movement (REM) sleep as well as irregular breathing and pulse rate with the body immobilised and extremely relaxed. REM sleep is also strongly associated with ones dream as this is the stage where most dreams occur [(Weiten (2004 6)]. Scientist suggests the reason for the extremely relaxed muscular activities is so one will not act out the dream physically. REM is important to daytime performance and may contribute to memory consolidation. EEG becomes desynchronized while EOG results stated that eye movement at this period will be darting back and forth, while muscles recordings from EMG demostrates relaxation reflexes. This stage has been said to be 'paradoxical' of sleep where EEG recordings are similiar towards a person being awake. Each of the sleeping cycle contains a number of REM sleep cycles [(Green, Muir, James, Gradwell, & Green (1996 3)].

At a typical 8hour sleep, each person will encounter about 4 to 5 bouts of REM sleep process. The sleep cycle will repeat about four times during a single good quality restful sleep, at which the REM will become gradually longer, from the initial 10 minutes to the final one which may last up to 90 minutes. NREM stages will progressively become shorter and stage 3 and 4 sleep will be omitted in the later cycles of sleep. For a young adult, REM will account for 25% of the total sleep time while slow wave sleep will account for 45% of the total sleep time. The ratio of REM and NREM sleep is dependant on age, where an infant may spend up to 50% in REM sleep, an adult is likely to only spend up to 20% in REM sleep. The sleep cycle of an individual depends on their own circadian rhythms and will differ between people. The amount of sleep needed, and the restorative quality of sleep is also different for each individual [(Weiten (2004 6)].

Supporting evidence

A research carried out by Dorrian, Lamond, van den Heuvel, Pincombe, Roger and Dawson (2006 [2]) showed that irregular sleep or sleeplessness by Australian nurses had a great impact on their performance. Government reported 31 deaths or serious harm to patients and 452 "very risky" incidents. And another study previously condusted showed a annual fugure of 2,324 serious medical events out of which half as preventable. Howver, researchers noted that nurses work long and irregular hours with inadequate breaks and rests. The research involves observation of regular and actual work hours, sleep hours and quality, fatigue and sleepiness of 23 full-time nurses working in urban hospitals for 644 days (377 shifts). Results showed that nurses struggle to keep awake during 36 per cent of shifts. Medium to high lelvels of stress was reported on 23 per cent shift and above modertate levels of metal exhaustion and tiredness were reported on 36 and 40 per cent of shifts, respectively. Nurses complained of difficulty having adequate sleep on 26.8 per cent of days. The final conclusion of the study was that "Australian nurses experience sleepiness and related physical symptioms at work and during their trip home…" and consiquently this lead to the "increased likelihood of making errors and decreased likelihood of catching some else'e errors" (p.1149).

In another research conducted by Baranski, Thompson, Lichacz, McCann, Gil, Pasto, & Pigeau (2007 [1]) the congnitive performance of team having sleep loss was studied. Sixteen teams each with 4 members were involved in decision-making process. All members were with 30 hours of sleep loss. It was found that sleep loss had a significant effec on decision-making accuracy and decison time. It was also found that the individual fatigue factor was mediated by being a part of group. Thus, sleep deficiency has a great impact on cognitive performance. However, while sleepy individuals are motivated more in teams than working individually.

Refuting evidence

Way forward (to do list)

1. Baranski, J. V., Thompson, M. M., Lichacz, F. M. J., McCann, C., Gil, V., Pasto, L., & Pigeau, R. A. (2007). Effects of sleep loss on team decision making: Motivation loss or motivation gain?. Human Factors, 49, 4, 646-660.
2. Dorrian, J., Lamond, N., van den Heuvel, C., Pincombe, J., Roger, A. E., & Dawson, D. (2006). A pilot study of the safety implications of Australian nurses' sleep and work hours. Chronobiology International, 23, 6, 1149-1163.
3. Green, R. G. Muir, H. James, M. Gradwell, D. & Green, R. L. (1996). Human Factors for Pilots (2nd Ed). U.K: Ashgate.
4. Schenck Carlos (2007). Sleep: The Mysteries, the Problems, and the Solutions. Avery. (NY, USA). 2007.
5. Richard Reinhart (1996). Basic Flight Physiology: Second Edition. McGraw-Hill Company. (NY, USA). 1996.
6. Wayne Weiten (2004). Psychology Themes & Variations. Thomson Learning Inc. (OH, USA). 2004.

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BBC Science - Sleep
More information about sleep, including tests to assess your level of tiredness.

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