By now we know what happens if we do not sleep, but little is known about what happens when we are asleep? Sleep occurs in recurring cycles of 90 to 110 minutes divided into two categories
1.Non REM (Rapid Eye Movement) Sleep
2.REM Sleep
The Non REM is sub divided into 4 stages
Step one Light sleep
At this stage we can be awakened by the slightest of noise, and the muscle activity slows down. We are partially awake and partially asleep.
Step two True sleep
This stage lasts for around 20 minutes and we enter this stage within 10 minutes of light sleep. The heart rate and the pace of breathing slow down making us more stable. True sleep accounts for the maximum part of human sleep.
Step three and four Deep sleep
Breathing and heart rate are at their lowest level as the brain starts sending delta waves.
At step four muscle activity is reduced considerably characterized by continuous rhythmic breathing. This is the deep sleep mode, if awakened at this stage we tend to be groggy and grumpy.
REM
The body is sleeping and numb but the brain is very active and this is the time when most of the dreams occur. Our blood pressure is on the rise and breathing becomes faster and heavier. We have around 4- 5 REM episodes at night.
After REM the sleep cycle restarts.
Pic courtesy Alzwww on www.flickr.com
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