A Healthy Sleep-Wake Cycle

Sleeping girl

Importance of Sleep

Sleep is something we do quite often, but do we really understand how critical it is to our health and wellbeing? The sleep-wake cycle is a fundamental process in our lives. It has been equated with several functions, including physical restoration, the optimization of waking neurocognitive and emotional functioning, and the overall promotion of health and survival.


Sleep and the Body’s Rhythms

Like most physiological and psychological functions that we humans depend on, our sleep demonstrates a rhythm. Each of our body’s rhythms is unique in terms of the time it takes to complete one cycle. For example, we have some very short rhythms (like our cardiac rhythm), and other very long ones (like the menstrual cycle). Sleep follows a circadian rhythm, which means that the cycle has an approximate length of 24 hours. An interesting fact is that circadian rhythms, which are intrinsic to humans, are not necessarily dependent on the presence of a light-dark cycle in our environment. Granted, we tend to synchronize the two, but circadian rhythms are expressed even when we humans are isolated from any temporal or environmental cues (Hales, Yudofsky & Gabbard, 2008).


Types of Sleep

It is easy for us to distinguish when someone is awake or asleep, but did you know that we have different kinds of sleep, and that while we are asleep we alternate between sleep types every 90 to 100 minutes?  The two primary states of sleep are (1) rapid eye movement (REM) sleep, and (2) non-rapid eye movement (NREM) sleep.


REM sleep: In the average young adult, REM sleep represents approximately 25% of time slept. REM sleep is characterized by rapid and random eye movements, as well as by low muscle tone (which actually paralyzes our bodies in order to prevent us from acting out our dreams) and by rapid but low–voltage brain waves that are very similar to those observed when we are awake. REM sleep is also the sleep stage in which dreaming primarily occurs. The REM stage gets progressively longer and more intense as the night progresses.


NREM sleep: The NREM sleep state is further divided into four stages that range from high arousability to low arousability.


o        Stage 1: In the average young adult, Stage 1 NREM sleep occupies only about 5% of sleep time. This stage is seen only during sleep onset and following the brief awakenings that occur throughout the sleep period.

o        Stage 2: In the average young adult, Stage 2 NREM sleep occupies about 50% of sleep time. During this sleep stage, we are no longer conscious or aware of our environment.

o        Stages 3 and 4: These NREM sleep stages are also known as ‘slow wave sleep.’ In the average young adult, these stages occupy about 20% of sleep time. They are characterized by presenting the slowest of brain waves (delta waves). These stages of sleep tend to occur early on in sleep, and diminish in length and intensity as the night progresses. The average person will have few indications of these two sleep stages during the second half of their sleep time.


Effects of Sleep Deprivation

The need for sleep in all of its stages is compelling. However, in today’s busy world, people are rarely getting the sleep they need. We must remain aware of the many negative effects that continuous sleep deprivation has, including changes in our emotions, behaviors, and mental processes, as well as negative biological effects (Moorcroft, 2003).



Do you feel you are sleep deprived sometimes or perhaps all the time? If so, what sort of effects do you think it has on your physical and emotional wellbeing? Based on the information about types and stages of sleep provided herein, of what kinds of sleep do you believe you get a sufficient amount? Is there a particular sleep type or stage in which you feel you are experiencing deprivation? What changes can you make in your life that might help you to get more of this kind of sleep? Or simply to get more sleep in general?





Hales, R.E., Yudofsky, S.C., & Gabbard, G.O. (2008). Textbook of Psychiatry, 5th ed. American Psychiatric Publishing: Arlington, VA.


Moorcroft, W.H. (2003). Understanding Sleep and Dreaming. Kluwer Academic-Plenum Publishers: New York, NY.



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