Sleep Occurs in Four Stages
During the sleep, homeostasis will fluctuate because sleep occurs on four stages (Davidmann 1998). The individual goes from awake to Stage 1, then to 2, 3 and finally 4. After spending about twenty minutes in Stage 4, individuals return to Stage 1 and progress back to Stage 4. The individual will continue to make these cycles throughout their sleep. Most individuals will experience about 4 to 5 cycles a night (Davidmann, 1998). During Stage 1 the individual will experience what has been named REM (Rapid Eye Movement). During REM the body will show more signs of consciousness by spontaneous muscle contractions, flagellate excretion, and oculomotor coordination (eye movement). The body will experience these tensions and reactions because this is the active time of sleep in the average human (Davidmann, 1998). REM is the time in which the individual will have their dreams. Nathaniel Kleitman discovered it in 1953. It always occurs in the lightest stage of sleep, Stage 1. It has been given its name because of the muscle contractions in the eye motor receptors. These electrical impulses originate from the brain stem and then travel to the eyes to produce imagery. The catalysts for these impulses are triggered by the subconscious mind and the emotions within it (Davidmann, 1998). The REM will usually begin ninety minutes after sleep is initiated and will last roughly ten to fifteen minutes. The REM will end and the individual will slip into deeper sleeps, until the forth stage is reached. Once this occurs the mind begins to come out of the deeper sleep stages until it reaches REM once again. The interesting factor is that each time the sleeper enters the REM phase of sleep the REM phase will increase in length. This repeats four to five times in the average sleep. The reason the dreams occur in the REM or the lightest stage is because this is the only stage in which the conscious mind can interpret the imagery of the subconscious. This is not to say the subconscious doesn t remain active in the deeper sleep stages but the conscious mind isn t alert enough to decipher the imagery the subconscious creates in deep sleep. REM is also interesting because if a person does not experience it they will suffer from various sleeping disorders because the body requires it. People who experience exaggerated REM will suffer from fatigue and sleep depravation while they are awake. Usually, a full-grown person has about 4 to 5 cycles of REM sleep, consisting of about 25% of a night s sleep. A newborn child s sleep can consist of as high as 50% REM type sleep (Davidmann, 1998).
+ Stage 1 is the lightest of sleep. There is often visual imagery involved. Images appear in the form of wandering or dream like thought, which can be controlled unlike a full dream state. Someone can be awakened by low volume sounds or slight touch. It often appears as a transitional state of sleep following arousal during the night. When stage one does reappear during sleep it only lasts thirty seconds to a minute (Carskadon 5-6). Young adults spend ten to fifteen minutes a night in Stage 1 sleep (Carskadon 6).
+ Stage 2 sleep may have some of the slower eye movement of Stage 1 and will but in general Stage 2 sleep is free of any eye movement. Another feature of Stage 2 is arousal. Since Stage 2 is a deeper than Stage 1 it will take more arousal to awaken a person from this stage of sleep (Carskadon 9).
+ Stage 3 sleep as well as Stage 4 is usually referred to as a slow wave sleep. There are no visible eye movements in this stage (Carskadon 10). It takes even more arousal than Stage 2 sleep to awaken a person from this stage of sleep. Most of the dreams remembered occur during Stage 3 sleep (Carskadon 11-12)
+ Stage 4 sleep is the deepest of sleep. This is where the body and mind gets the most rest. In this stage of sleep people begin their dreams. When a person is dreaming you can visually tell by the movement of the eyes. Scientists and theorists measure deep sleep by REM (Rapid Eye Movement). What they measure is the amount of time your eyes moves in Stage 4 sleep and also brain activity along with frequency. Once again much more arousal is needed to awaken a Stage 4 sleeper (Carskadon 14-19).
Carskadon, Mary. Stages of Sleep . Encyclopedia of Sleep. 1993 Ed.