While sleep is still something of a mystery, researchers have determined that there are distinct stages of sleep that a person goes through if they get a full night's rest. The exact function behind each is still being studied, but scientists have come up with at least a few reasons behind the stages. When you sleep, your brain goes through 5 different stages of sleep.
Usually sleepers pass through five stages: 1 - 4 Non-REM sleep and REM (rapid eye movement) sleep. These stages progress cyclically from 1 through REM then begin again with stage 1. Each stage of sleep exhibits a different brain wave activity and each serves a different purpose.
Non-REM sleep. The brain is quiet, but the body may move around. Hormones are released into the bloodstream and our body repairs itself after the wear and tear of the day.
There are 4 stages of non-REM sleep:
Pre-sleep - the muscles relax, the heart beats slower and body temperature falls.
This state has many names such as day dreaming, zoning out and many others. It is the first step of falling asleep. In this stage, a person is still somewhat aware. Sounds may be enhanced and the awareness is being shifted inwards. During stage 1, sleepers may suddenly feel out of balance as if they were falling, or make jerky movements with their whole body.
This is also the most effective stage of sleep when taking a nap. It allows the brain to rest and replenish without shutting down the body. Most people who sleep normally stay in this stage for five minutes or less, but someone with insomnia might stay for much longer.
Light sleep - we can still be woken easily without feeling confused.
Stage 2 is categorized by sudden bursts of brain activity. This is the period when the body is shutting down. It may be accompanied by random arm and leg movements. The on-off transition into deeper sleep ensures that the body is in a safe and secure position before completely shuts off.
In this stage the heartbeat and respiration slow and become very regular. The body relaxes more deeply. Sleepers can still be aroused, but not so easily as when they're in stage 1. Most people spend about 30 minutes in stage 2. Stage 2 accounts for about 50% of all sleep time.
Slow wave sleep - our blood pressure falls, we may talk in our sleep or sleep walk.
This is known as deep sleep and is very hard to rise from. During deep sleep, blood pressure, breathing, and heart rate are at their lowest of the day. Blood vessels are fully dilated and blood is allowed to flow to areas that are normally turned off. Muscles are able to be nourished and repaired.
Deep "slow wave" sleep - we become very hard to wake.
Stage 4 is categorized by the deepest, most restorative sleep and if awoken from may result in grogginess. This is when the body has completely shut down and is rejuvenating.
During a normal night, sleep stage 4 which is for really deep replenishment of the body, is only reached during the first few cycles of sleep. It may even never be reached if the body is kept inactive.
Rapid Eye Movement (REM) sleep. It comes and goes throughout the night, and makes up about one fifth of our sleep time. During REM sleep, our brain is very active, our muscles are very relaxed, our eyes move quickly from side to side and we dream.
During REM sleep, your eyes move rapidly back and forth under closed eyelids. Here, person is temporarily paralyzed, apparently Mother Nature's safeguard to prevent the physical acting out of dreams.
REM sleep accounts for about 20-25% of total sleep time in a normal adult.
During sleep, the brain cycles from sleep stage 1 to sleep stage 5 numerous times. Each sleep cycle lasts about 90 minutes.
Early in the night, the brain spends more time in sleep cycles 3 & 4 and proceeds to spend more and more time in REM sleep.
In order for our sleep to be effective we must have enough time to allow for several cycles of Non-REM and REM sleep. If we miss out on any of these stages of sleep then our sleep is less restful. When considering how to get a good night sleep it is important to look at lifestyle, diet, exercise and other factors that affect our sleep.