I’ve heard about sleep cycles. How does sleep work and how do its cycles affect me?

28 May, 2011

“The bed is a bundle of paradoxes: we go to it with reluctance, yet we quit it with regret; we make up our minds every night to leave it early, but we make up our bodies every morning to keep it late.”  Charles Caleb Colton

Far from being a time when the brain shuts down, sleep is actually a pretty active period for the brain, and it affects both our physical and mental health.

While our bodies rest and recharge, we go through five main stages of sleep divided into rapid eye movement (REM) sleep in which most dreaming occurs, and non-rapid eye movement (non-REM or NREM) sleep during which one doesn’t dream as much.

REM sleep is called that literally because our eyes tend to move rapidly from left to right under our eyelids during that stage, becoming more relaxed during non-REM sleep.

The first four stages of sleep are non-REM, with the final one, stage 5, being REM.  These stages repeat throughout the night with a cycle of about 90 to 110 minutes (60 minutes in infants).  The cycle repeats between 4 and 6 times a night, and if interrupted will affect the quality of sleep.

Stage 1

During stage 1 or “drowsy” sleep, we are in a very light stage of sleep in which we can wake easily.  Our body temperature drops slightly, the muscles relax and our breathing slows.  In most people, this stage lasts from a few seconds to about ten minutes.  If we wake up during this period, we often don’t even know that we have been asleep.

Stage 2

Stage 2 of the non-REM sleep is also light.  Muscles continue to relax, heart rate and breathing slow further and the body temperature continues to drop.  During stage 2, the body starts the repair process.

Stage 3 and 4

During Stage 3 and 4, muscle activity stops almost completely, and the body’s repair mechanisms really get to work.  It is very difficult to awaken someone in this stage.

People with sleep disorders tend not to spend as much time in these particularly restful stages as good sleepers do, which may explain why sufferers don’t feel as well rested even after a reasonable night’s sleep.

Stages 3 and 4 are also known as Delta sleep because of the shape of the brain waves when tracked by an EEG (electroencephalogram), a recording of the brain’s electrical activity.

Stage 5

Finally, the brain enters REM sleep in Stage 5.  Sleep researchers consider this stage to be vital for mental filing and restoration and it will typically account for between 20-25% of total sleep time in most adults.

The length of REM sleep tends to increase in each cycle from about 5 minutes at the beginning of the night to as much as 30 minutes or more by the end of the night.  During REM sleep, our breathing can be irregular, our heart rate and blood pressure rise and our muscles are relaxed to the point of complete inertia.

REM sleep appears to be particularly important for the development of the brain.  Babies in particular spend much of their sleeping time in REM sleep.

As you can imagine, this cycle is extremely delicate and complex, and can easily be disturbed.  All sorts of outside stimuli and other factors can affect the architecture of the sleep cycle, with each having its impact on different stages.

Alcohol, tranquilizers and sleeping pills can affect your deep Delta sleep in stages 3 and 4 when much physical repair work is going on.  If sleep is interrupted in this stage, one can wake feeling out of sorts, with a general sense of being unwell.

Other drugs, such as marijuana, may impair REM sleep (stage 5), possibly affecting memory and learning.

External noise, discomfort, indigestion, excess light, even electromagnetic waves can all disturb various stages of sleep and leave us below par the following day.

Did you know? Elephants sleep lying down during REM sleep but standing up during NREM sleep!

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