What Is "Sleep?"
For most of human history, "sleep" was considered to be little more than "not awake".
It was simply a period of time that you were not conscious and mostly happened during the night.
Now, thanks to pioneering research done over the last few decades, sleep is recognized as a critical component of human health and has several parts, or stages, that were not previously known.
In fact, sleep occurs in very distinct stages that continually cycle throughout the sleeping period.
The amount of rest that you get is a function of both total time spent in sleep AND the amount of each of the various stages as well.
Far from being unaware or unconscious, the human brain remains active throughout the sleeping period and each of the different stages of sleep is measured by a unique pattern of brain waves.
At its most basic, sleep is comprised of two basic parts known as Rapid Eye Movement (REM) sleep and non-REM sleep which is sub-divided into four additional stages.
Most frequently we begin sleeping in what is known as "stage 1 non-REM" sleep.
During this part of the sleep cycle, sleep is not deep and you are easily awakened by disturbances.
Physically, while in this stage, eye movements are very slow and there is very little muscular activity.
Next, you enter "stage 2 non-REM' sleep.
In stage 2, eye movements stop completely and your brain waves slow with intermittent flare ups of more rapid waves.
Now you enter "stage 3 non-REM" sleep.
This stage is marked by even slower brain wave activity, but still with very occasional spates of heightened activity.
By the time "stage 4 non-REM" sleep arrives the brain is developing even slower brain waves almost exclusively.
Stages 3 and 4 are considered to be "deep" sleep and it is difficult to be woken up.
It is this part of the sleep cycle that is thought to be the most restorative overall and most necessary to be well rested and energetic during the next day.
In "REM" sleep, the eyes move rapidly behind closed eyelids and breathing is more shallow, and fast.
Also, the heart rate and blood pressure increase and your extremities are paralyzed temporarily to prevent acting out the dreaming that is most prevalent during the REM stage.
The first REM stage occurs about 90 minutes after falling asleep and this cycle of REM and non-REM repeat continuously through the night.
As the night wears on REM stages become longer and stages 3 and 4 of non-REM sleep become correspondingly shorter so that, in the morning, you will have spent most of your sleep time in stages 1 and 2 non-REM sleep and in REM sleep as well.
In terms of percentages, stages 1 and 2 non-REM sleep make up almost 50% of sleep time, stages 3 and 4 and REM sleep are about 25% each.
It was simply a period of time that you were not conscious and mostly happened during the night.
Now, thanks to pioneering research done over the last few decades, sleep is recognized as a critical component of human health and has several parts, or stages, that were not previously known.
In fact, sleep occurs in very distinct stages that continually cycle throughout the sleeping period.
The amount of rest that you get is a function of both total time spent in sleep AND the amount of each of the various stages as well.
Far from being unaware or unconscious, the human brain remains active throughout the sleeping period and each of the different stages of sleep is measured by a unique pattern of brain waves.
At its most basic, sleep is comprised of two basic parts known as Rapid Eye Movement (REM) sleep and non-REM sleep which is sub-divided into four additional stages.
Most frequently we begin sleeping in what is known as "stage 1 non-REM" sleep.
During this part of the sleep cycle, sleep is not deep and you are easily awakened by disturbances.
Physically, while in this stage, eye movements are very slow and there is very little muscular activity.
Next, you enter "stage 2 non-REM' sleep.
In stage 2, eye movements stop completely and your brain waves slow with intermittent flare ups of more rapid waves.
Now you enter "stage 3 non-REM" sleep.
This stage is marked by even slower brain wave activity, but still with very occasional spates of heightened activity.
By the time "stage 4 non-REM" sleep arrives the brain is developing even slower brain waves almost exclusively.
Stages 3 and 4 are considered to be "deep" sleep and it is difficult to be woken up.
It is this part of the sleep cycle that is thought to be the most restorative overall and most necessary to be well rested and energetic during the next day.
In "REM" sleep, the eyes move rapidly behind closed eyelids and breathing is more shallow, and fast.
Also, the heart rate and blood pressure increase and your extremities are paralyzed temporarily to prevent acting out the dreaming that is most prevalent during the REM stage.
The first REM stage occurs about 90 minutes after falling asleep and this cycle of REM and non-REM repeat continuously through the night.
As the night wears on REM stages become longer and stages 3 and 4 of non-REM sleep become correspondingly shorter so that, in the morning, you will have spent most of your sleep time in stages 1 and 2 non-REM sleep and in REM sleep as well.
In terms of percentages, stages 1 and 2 non-REM sleep make up almost 50% of sleep time, stages 3 and 4 and REM sleep are about 25% each.
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