Stages of Sleep
Many people automatically assume that sleep is one continuous stage. You close your eyes, perhaps you dream a bit, then you wake up. However, scientists have discovered that this isn’t really the case! Through numerous studies, they’ve found out that there are several different stages of sleep and that people go through these stages a few times each night. This is called the sleep cycle.
The stages can be categorized into two major groups: REM (which stands for rapid eye movement) sleep and non-REM sleep (which contains stages 1 to 4 of the sleep cycle). Basically, a person progresses from Stage 1, 2, 3, and 4, goes back to Stages 3, 2 and 1, then proceeds to a short period of REM sleep. The cycle begins again at Stage 1 onward, with the sleeper spending less time in Stage 3 and more time in REM sleep as the night goes on. REM sleep lasts from 90 to 120 minutes each night, while non-REM sleep takes up four to seven hours each night.
Stages 1 and 2
But how are these stages different from each other? Well, it all boils down to brain activity. During Stage 1, your eye movements slow down and you might experience a falling sensation as well as some muscle contractions. You sleep lightly during this stage and can be easily roused if someone wakes you up or if there is activity and/or loud noises nearby. During Stage 2, your brain waves slow down but are punctuated by a few rapid waves, and your eye movements completely stop. Your heart rate and body temperature also drop.
Stages 3 and 4
Stages 3 and 4 are characterized by slow brain waves, and together they form the “deep sleep” part of non-REM sleep. During these stages, it would be harder to wake you up and, when you do get roused, you’ll be disoriented for several minutes. The American Academy of Sleep Medicine has combined the two stages and now consider non-REM sleep to have three stages only.
REM sleep, meanwhile, is hallmarked by incredibly fast brain waves. In fact, during this time, your level of brain activity is almost the same as when you’re awake, which has caused scientists to call REM sleep as “paradoxical sleep”. This is when you mostly have your dreams and, when you wake up in the middle of this stage, you’ll find it easy to remember what your dreams were all about.
During REM sleep, your eyes exhibit fast, jerking movements, which give rise to the term “rapid eye movement” that describes this stage. You also exhibit faster and shallower breathing, and your limb muscles experience temporary complete paralysis so your entire body doesn’t move. This is in contrast with non-REM sleep, during which you make limited movements and even change your position on the bed.
Different things happen in your body during the different stages of sleep. During Stages 2 and 3, for example, your brain processes the information it has gathered during the day and consolidates them into your memory. Information processing and memory consolidation also happens to some extent during REM sleep.
Stage 3 is the time when your body heals itself. During this stage, your cells and tissues are repaired while new ones are grown, and your immune system is strengthened. Your body also releases hormones, including growth hormones that are important in the development of your bones and muscle.
With these in mind, it’s easy to see that each stage of sleep is important. Those who don’t get enough sleep, such as people with sleep apnea, will find that missing one or more of these stages can have negative consequences. Missing Stage 3 sleep, for example, means that your body doesn’t get the chance to repair itself and grow new muscles, bones, and other tissues. You’ll also have a weaker immune system and have a higher chance of developing illnesses.
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