Amazing artwork from whisperfall.
What happens when we sleep?
Imagine you get a healthy 8-9 hours of sleep without waking up constantly in the night (hah, I wish). What would happen in these 8-9 hours?
When we sleep we go through a reoccuring cycle that repeats itself approx every 90-110 minutes. During this cycle we experience NREM (non-rapid eye movement) and REM (rapid eye movement) sleep. NREM is split into four stages and occurs 75% of the night, whilst REM only occurs 25% of the night.
NREM occurs when we begin to fall asleep. We enter stage 1 when we are between falling asleep and being awake. Stage 1 is considered “light sleep”. Our muscle activity slows down and twitching is normal. It is very easy to wake someone who is in stage 1 of NREM.
We enter stage 2 of NREM after around 10 minutes of light sleep (stage 1). Stage 2 lasts around 20 minutes and accounts for the largest part of human sleep. Breathing and heart rate start to slow down, body temperature drops and we become disengaged from surroundings.
After 20 minutes of stage 2, we enter stage 3. The brain begins to produce delta waves, which is a type of wave that has a high amplitude and low frequency. Breathing and heart rate are at their lowest levels during this stage.
Stage 3 and 4 are known as deep sleep. If we are awakened during deep sleep we will often feel disorientated and some of us grumpy/annoyed. It is normal for children to experience bed-wetting, night terrors or sleepwalking during stage 4. A lot happens during stage 3 and 4; muscles are relaxed, blood pressure drops, breathing becomes slower, blood supply to muscles increases, tissue growth and repair occurs, energy is restored and hormones are released (such as growth hormone which is essential for growth and development).
In my previous post about sleep, I mentioned the following:
Sleep loss may increase the risk of obesity because the chemicals and hormones that control appetite and weight gain are released during sleep.
The release of these hormones occurs in stage 4.
After NREM we experience the first REM period (usually begins about 70-90 minutes after we fall asleep). We are not conscious during this but the brain is still very active. The REM period is when most dreams occur and our eyes dart around (rapid eye movement). Breathing rate and blood pressure rise and our bodies are effectively paralysed. The paralysation of our bodies could be nature’s way of preventing us from acting out our dreams.
After REM sleep, the whole 90-110 cycle begins again and we start with stage 1 of NREM sleep! Unless, of course, are disturbed by annoying relatives or cats.
More on sleep: