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Although it’s common to think of sleep as a time of “shutting down,” it is actually an active physiological process. While our metabolism generally slows down during sleep, all major organs and regulating systems continue to function normally.
REM and Non-REM
Sleep can be categorized into two distinct types: Rapid Eye Movement (REM) sleep and non-REM (NREM) sleep. During non-REM sleep there is a reduction in some physiological activity. As sleep gets deeper, brain waves get slower, breathing and heart rate slow down and blood pressure drops.
Once asleep, about every 90 minutes we pass through a cycle of five distinct sleep stages. The non-REM phase consists of the first four stages. Non-REM sleep is usually dream-free 90 percent of the time.
Stage One
Stage 1 is a time of drowsiness or the transition from being awake to falling asleep. The heart rate drops further, your muscles relax and breathing becomes more irregular. During stage 1 sleep, some people experience an occasional muscle jerk, often accompanied by a falling sensation. Hence the term “falling asleep.” This muscle jerk is similar to a jump when we are startled. The muscle contraction is called hypnic myoclonia or hypnic jerk. People awakened at this time might say they weren’t sleeping.
Stage Two
Stage 2 is a period of fairly light sleep. Eye movements stop. Brain waves become slower, with occasional bursts of rapid waves called brain spindles, coupled with muscle contraction and relaxation. The heart rate and body temperature decrease. Most people would say they were asleep if awakened.
Stages Three and Four
We refer to Stages 3 and 4 as slow wave sleep. New brain waves appear called delta waves. These waves are very large and slow, and indicate a further loss of consciousness with no eye movement, and a move to deeper sleep as the body becomes immobile. It is most difficult to be awakened during these two stages of sleep, and people who are awakened may feel groggy or disoriented for several minutes. It is during these sleep stages that children experience bed wetting, night terrors or sleepwalking.
Stage Five
The 5th stage is the REM sleep stage. During this stage, intense brain activity occurs. Brain waves are fast and desynchronized, similar to those in a waking state. Breathing becomes quicker, irregular and shallow, eyes move rapidly in various directions and limb muscles can become temporarily paralyzed. Heart rate increases and blood pressure rises. This is also the stage where most dreams take place.
Dream Sleep
REM sleep is a time of high emotion and both males and females appear to be sexually aroused. When people awaken during REM sleep they often describe strange and illogical stories or dreams. (See dreams).
The first REM sleep period occurs about 70 to 90 minutes after we fall asleep. A complete sleep cycle of all 5 stages takes 90 to 110 minutes on average. A good night’s sleep will have 4 to 6 complete sleep cycles. The first sleep cycles each night contain relatively brief REM periods and longer periods of deep sleep. As the night progresses, REM sleep periods become longer while deep sleep periods become shorter. By morning, we spend nearly all our sleep in stages 1,2 and REM.
Insomnia Causes
Since sleep and being awake are influenced by different neurotransmitter signals in our brain, food and drugs that change the balance of these signals affect whether we feel alert or drowsy, and how well we sleep. Caffeinated drinks such as coffee, colas and energy drinks and drugs such as diet pills and decongestants stimulate parts of the brain that can cause insomnia. Heavy smokers often sleep very lightly and have shorter periods of REM sleep. Smokers also tend to wake up after only 3 to 4 hours of sleep due to nicotine withdrawal. Many people who suffer from insomnia try to relieve the problem with alcohol – the so called “nightcap.” While alcohol does help people fall asleep, it also robs them of REM and deep restorative sleep. Instead, it holds them in the lighter stages of sleep.
Playing Catch-Up
Abnormally hot or cold temperatures can also disrupt our REM sleep. If our REM sleep is disrupted one night our bodies don’t follow the normal sleep cycles the following night. Instead we often slip directly into REM sleep for extended periods until we catch up. Then we return to our normal sleep cycles.
This report is not a diagnosis. We hope this information can guide you toward improving your life.
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