What are the Different Stages of Sleep?
Did you know that there are stages of sleep? What and how? Read on.
While science-fiction books and movies often tout the now cliché line that ‘space is the final frontier’, in actuality, we don’t have to look that far to find a realm that is still full of new frontiers, in which the mysteries far outweigh the facts. Much of this territory still remains unexplored and the answers we find often lead to even more intriguing questions. That realm is a place most of us go for at least a few hours every 24-hour cycle. It’s the process known as sleep.
In simple terms, sleep is a period of absent consciousness that gives the body time to rejuvenate and refresh itself. However, such a simple explanation belies the complexities of sleep, which hint at the mysteries that lie underneath its surface. Many of these mysteries scientists have yet to fully understand, for they have as much to do with the brain, a still largely uncharted territory, as sleep itself.
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Despite the decreased ability of a sleeper to react to outside stimuli, the brain itself never sleeps, and there’s even a point during REM sleep in which the brain patterns match those of a person wide awake. Even so, sleep does affect the brain, for the stages of sleep are marked by either increased or decreased brain wave activity.
In actual fact, there are five stages of sleep that can be divided into two broad categories: non-REM sleep (or non-rapid eye movement sleep) and REM sleep (or rapid eye movement sleep). The first four stages of sleep are part of the first category and stage 5 is simply REM sleep.
The five stages of sleep are as follows:
Stage 1: This is a stage of light sleep, a transition period between waking and sleeping whereby the brain waves change from alpha waves, or being awake, to theta waves, which are very slow brain waves. If a person is awoken from stage 1 sleep, they may not have realized they were ever asleep. Some muscular activity and awareness of the external environment diminishes. In addition, hypnagogic hallucinations, such as hearing someone call your name or feeling like you are falling, may also occur in this state. It normally lasts about five to ten minutes.
Stage 2: This stage of sleep is characterized by rapid, rhythmic brain wave activity known as sleep spindles. Not surprisingly, it is not abnormal for a sleeper to be suddenly startled awake for no apparent reason during stage 2 sleep. As the stage progresses, heart rate decreases and body temperature drops. The diminishing of muscular activity and awareness of the external environment that began in stage 1 completes itself in stage 2, both gradually disappearing. This stage lasts for twenty minutes at a time, but actually makes up about forty-five to fifty-five percent of an adult’s sleep time, or the majority of a good night’s sleep.
Stage 3: This is the beginning of Delta sleep as Delta brain waves, or extremely deep and slow brain waves, begin to appear. For this reason, stage 3 is the transition between light and deep sleep.
Stage 4: Stage 4 sleep is known as Delta sleep because it is characterized by Delta waves. Consequently, it is the deep phase of the five stages of sleep and lasts approximately thirty minutes. Furthermore, it is also the stage where parasomnias; such as sleepwalking, sleep talking, bedwetting, and night terrors; can occur.
Stage 5: While the previous four stages of sleep are often said to be ‘quiet sleep’, stage 5 is characterized as ‘active sleep’. Increased brain activity and respiration rate occur during this phase, though it is most noted for rapid eye movement beneath the closed lids. For this reason, it’s also known as REM sleep. Somewhat of a contradiction, the brain and other body functions speed up while the muscles relax. This may be due, in part, to a bodily defense, as dreams occur most during REM sleep because of increased brain activity. However, in order to keep the sleeper from acting out such dreams and possibly hurting themselves in the process, the body paralyzes itself during this stage of sleep.
The stages of sleep can complete more than 1 cycle a night
Though the body may enter each stage in sequence to begin with, it does not necessarily follow that order throughout the night. Normally, one cycle goes through the following sequence; stage 1, stage 2, stage 3, stage 4, stage 5, stage 4, stage 3, stage 2, and stage 5; and the body can complete four or five cycles a night. As each cycle passes, stage 5 (REM sleep) increases in duration, only lasting about ten minutes at first, and lengthening as much as ninety minutes as the night progresses.
Not surprisingly, scientists have yet to understand how all these stages of sleep affect the brain. In our limited understanding, we may liken it to a computer that takes in information all day and then when night comes goes into an alternate state of consciousness where it downloads the material and files it into various slots for easy access later on. However, sleeps does more than just help the brain. It is also a heightened anabolic state that augments the growth of the immune, nervous, skeletal, and muscular systems. Like an auto-pilot janitor system that automatically turns on after the lights go out, it cleans, rejuvenates, checks, repairs, and tests all bodily organs and functions. Far from being a waste of time, it is a function that normal, healthy human beings need in good supply. If the demands of sleep are not met a cumulative effect known as sleep debt will occur that results in mental and physical fatigue, which will adversely affect the performance of the body throughout the day.
Not surprisingly, the body relies on sleep so much that if it does not get it, it will try to compensate by sending the consciousness into little cat naps throughout the day that the person has little control over. Subsequently, a good night’s sleep is imperative if one wishes to wake up refreshed and rested and ready to start the day with all mental and physical capabilities at hand. Another thing we’ve learned here is that these five stages of sleep are very important for us to experience as it will definitely have influence with our body and brain – one way or another.