Understand Your Sleep Cycles

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so sleep is made up of stages and cycles
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and each stage occurs one after the
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other in a similar loop to the figure
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that you see above my head here and once
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each of those stages is complete they
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then repeat in what's called a cycle now
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each one of these sleep cycles takes
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about 90 minutes to complete and there
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are about four to six cycles per sleep
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interval as we go to bed and wake up
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there's about four to six of
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these and Sleep can be thought of as
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breaking down into two different types
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which we will talk about here moving
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forward in this lecture these types are
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considered to be NRM or what's called
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nonrapid eye movement sleep or rapid eye
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movement sleep and I'll explain a bit
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here about what that actually means so
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we'll start by talking about the various
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stages of sleep and the first stage that
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we'll talk about is what's called stage
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one sleep so stage one sleep is light
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sleep it lasts anywhere from about 1 to
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5 minutes and it's during this stage
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that we start to experience drops in
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heart rate relaxation of the musculature
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and also a reduction in our breathing
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rate it's also during this stage of
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sleep that we experience a hypnic jerk
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now a hypnic jerk is a feeling that
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we're falling and we jerk awake and it's
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considered to be a miscommunication
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between the brain and the body where the
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brain perceives that the body is falling
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simply because the body's relaxing and
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this may wake up your partner or those
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around you but typically people are able
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to fall back into stage one sleep right
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after they wake up now following stage
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one sleep we reach what's called NRM
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stage two sleep and this stage of sleep
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lasts anywhere from about 20 to 25
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minutes and it's during this stage of
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sleep that we start to see a decrease in
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our body temperature and this decrease
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in body temperature is essential for our
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progression into the later stages of
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sleep and this is why some individuals
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actually reduce the temperature in the
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room prior to going to sleep they set
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their thermostats to something like 68
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or 69 degrees and this really
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facilitates a cooling of the body so
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that you can progress and rest more
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effectively it's also during this stage
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of sleep that we experience what's
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called a sleep spindle and this is a
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burst of brain activity that is
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considered to be a function where we are
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blocking out noises in our external
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environment and it's almost said to be
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the brain's do not disturb mode that's
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getting turned on so that we can
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progress into deeper stages of sleep so
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moving next into some of the deeper
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stages of sleep and starting first with
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NRM stage three sleep or what's actually
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called deep sleep now this stage of
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sleep lasts anywhere from about 20 to 40
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minutes and it is during this stage of
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sleep where we begin to see improvements
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in our body's ability to heal itself we
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see improvements in muscle recovery and
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improvements in other organ systems and
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part of the reason for this is that
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growth hormone which is a hormone that
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helps our body recover overall is
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beginning to elevate during this time
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period additionally our brain waves are
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beginning to slow down during this
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period of time which facilitates a drop
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in energy expenditure in our body and
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it's also quite difficult to wake up
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during this period now for instance if
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your alarm clock goes off when you're in
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one of these stages of sleep stage three
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or stage four which we'll talk about
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next you feel quite groggy waking up and
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it's it's quite difficult to wake up in
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this stage versus let's say NRM stage
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one or NRM stage two which we had talked
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about
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previously so following this NRAM stage
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three phase of sleep we move next into
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sleep now sleep is also about 20 to 40
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minutes and it's during this period of
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time where that growth hormone that
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facilitates recovery is at its greatest
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we also see that dreams are occurring
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during this stage and our muscles are
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essentially paralyzed we're really not
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moving our body at all during this stage
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and it's considered that this stage of
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sleep is essential for memory
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consolidation and our ability to focus
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cognitively as we move through our day
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it's an important stage as well for
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consolidation of emotional effects
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emotional experiences that we've had
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through the day and it's generally
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considered to be the most robustly
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helpful stage of sleep for processing
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our mental state and really these are
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the the four essential stages of sleep
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and it can be quite difficult to
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distinguish between all four of them but
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primarily these last two stage three and
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stage four which are often grouped
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together and can be difficult to uh to
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tell apart