When you see someone sleeping, it usually looks like their bodies and brains are doing very little. They just lie there and breathe and it seems as if there isn’t much else going on. In fact, until the 1950’s, scientists believe that the body simply entered into a phase of shutting down during sleep, assuming that nothing was happening.
As it turns out, sleep is much more complicated than it originally seemed. Scientists have now learned that, underneath the surface, all kinds of things are going on. These processes that your brain goes through during sleep provide the rest and reboot that the body and brain need in order to function properly the next day.
While you are sleeping, your body and brain are going through a repeated cycle of activity that is made up of four different stages, including REM. Most people have heard of the REM sleep stage, which refers to Rapid Eye Movement. But did you know that there are three critical other stages of sleep that you pass through several times throughout a typical night?
Let’s take a look at what the different stages of sleep are and how they function.
What are the Stages of Sleep?
Sleep cycles through these three different stages of Non-REM Sleep, plus REM:
The first stage of sleep is very light. You tend to drift in and out of sleep very easily and it’s easy to be brought back into awareness from this stage. Your brain is producing alpha and theta waves while in Stage 1. During the stage, the muscle activity is slower and the eyes tend to move very slowly. Some people find that this stage of sleep brings with it that familiar sensation of falling that causes sudden muscle contractions. This is the stage entered into when people refer to taking a “catnap”.
During this stage the sleep cycle deepens, brain waves increase and then slow down, producing what is known as sleep spindles. Eye movement stops altogether during this phase of sleep. The brain will have only occasional bursts of rapid activity while the heart rate slows down and the body temperature begins to drop. If you’re taking what many people refer to as a “power nap”, you’ll want to wake up after this stage of sleep to feel energized for the rest of the day. This is usually at about 20 minutes into the sleeping cycle.
While there used to be both stages 3 and 4, the two have now been combined into this one stage. Delta waves begin to appear in the brain during this stage, which is characterized by extremely slow brain wave movement with smaller, quicker waves interspersed throughout. This is when sleep occurs and it is difficult to wake someone while they are in this stage of sleep and the body is less responsive to stimuli from the outside world.
This time is when parasomnias happen, such as sleep walking, talking, bedwetting or night terrors. When someone is awoken from sleep in this stage, a sense of disorientation is often experienced before complete wakefulness occurs.
During the Rapid Eye Movement (REM) stage of sleep, brain waves are similar to those found during wakefulness. The eyes are closed but moving about significantly, and the body is still—almost paralyzed. Breathing becomes more rapid during this stage, heart rate and blood pressure increase, and the body is less able to regulate its temperature during this stage of sleep.
REM sleep is when the most vivid of dreams tend to occur. If a person wakes up just after an REM sleep cycle, they may remember their dreams the next day. But most often, people don’t remember the dreams that they have during the REM sleep stage.
What Are Sleep Cycles Like?
For most people, a complete cycle of sleep typically lasts between 90 and 110 minutes until full completion. Each stage within that cycle lasts somewhere between 5 and 15 minutes. Sleep cycles can change in the night, with the REM stages of sleep lasting for shorter periods of time earlier in the night and longer REM stages as the night progresses.
The four stage of sleep are not necessarily cycled through in order from 1-4. The order can change a bit, but a typical sleep cycle might look like this:
Stage 1—Stage 2—Stage 3—Stage 2—Stage 1—REM Sleep
A person will typically go through approximately 4 or 5 cycles of sleep per night with the first lasting only around 90 minutes and the following taking between 100 and 120 minutes for each cycle to complete. As the night progresses, the stages of deep sleep that include very slow brain waves might last longer.
Stage 3 is the deepest part of the sleep cycle and provides the most restoration to a person while reducing the need for sleep. If a person cannot achieve a satisfactory amount of deep sleep in the night, then they will not feel well-rested the next day. Even if a person gets the proper number of hours of sleep at night, they will still feel tired the next day because their Stage 3 sleep has been hijacked.
It is during the deeper stages of sleep that Human Growth Hormone is released, which repairs muscles and tissues while restoring energy to the body. Children who are chronically sleep deprived may not be small in stature and not grow up to their full potential due to a lack of growth hormone. The immune system is also given a boost during this stage, making it critically important for maintaining health.
How Age Affects Sleep Cycles
As people get older, they may find that their sleep cycles change because their bodies have different needs. Everyone knows that babies spend a large amount of their time sleeping, and about half of that sleep is spent in the REM stage. Adults spend about half of their time sleeping in Stage 2, and 20% in REM sleep. As adults grow in age, they tend to spend less and less time in REM sleep, and they usually need less sleep in general.
Getting the right amount of all of the sleep stages at night is critical to being able to live your life well during the day! Practicing healthy sleep hygiene, sleeping on a comfortable mattress, and checking with your doctor if you have sleep troubles will all work to improve your sleep—making you a happier, healthier, more productive human during all of your waking hours.