Sleep cycle refers to the stages of sleep a person under go while sleeping. There are 4 stages of sleep that every person undergoes. On average, each cycle is consist of 90 to 110 minutes. Each person undergoes 4 to 6 cycles per night.
There are four stages of sleep:-
- NREM stage 1 (Non-rapid eye movement sleep)
- NREM stage 2
- NREM stage 3
- REM sleep
NREM Stage 1
Non rapid eye movement is the first stage of cycle. In this stage, person moves from awake stage to asleep stage. When a person enter in this stage, his brain activity, breathing, eye moment becomes slow and calm.
In this stage, person can feel hypnic jerk as sudden involuntary movement of legs, hands or any dreams that wake you up suddenly.
NREM Stage 2
Stage 2 is a stage where a person spend most of their sleep time. It count for 50 percent for your daily sleep. For the first sleep cycle, this stage is remain for 10 to 25 minutes, but in later stages the time for this stage increases.
This stage is protected by spindles and k complexes strike in the brain. See there are chances of getting wake up due to noise outside.
Sleep spindles is the fast brain activity that is produced to signal brain to avoid external noise. It helps to not allow external noise to enter into the conscious mind so as to person remains in sleep for more time. This spindles deals with low noise things only.
K-complexes is a more louder and stronger brain activity that prevents person from waking up even in the noise. During this sparks, brain assess the noise if it does not harmful then it decide to remain in the sleep. So, it is deciding phase if the noise is high than person can wake up. This k complex is also supports in the memmory consilidation, like building new memmories.
When a person take a nap in day, for 20 to 30 minutes he usually achieve this second stage of NREM sleep. As this stage ends, the person wake up as refresh and feels better with feeling of better memmory functions.
NREM stage 3
This is also called as deep sleep. This stage last for 20 to 40 minutes.
This stage is the deepest state of sleep. In this state a person is difficult to wake up. It is a phase of restoration where body repairs muscles, memmory and immune system restores.
In this phase,body release human growth hormone (HGH) for tissue growth, muscle recovery and cellular repair. Cytokines is release a protein that targets the inflammation and infetion. So, if one avoids the deep sleep it leads to weaken the immune system.
This sleep is very deep, as it causes low blood pressure, heart rate, brain activity is at lowest. If you wake up suddenly then it may cause a lost, unconsciouss feeling for first few minutes after wake up.
The consciouss mind is completely off in this stage, sometimes involuntary motor activity occurs, causing sleepwalking, sleep talking and night terrors.
REM Sleep
Rapid eye movement, starts after dreaming stage. In initial cycle it last for 5 to 10 minutes later increases to an hour as morning occurs.
This is called rapid eye movement because eyes move quickly in different directions in eyelids. This phase is highly active in the brain that you actively seeks into the vivid dreams, heart rate increases, blood pressure and eye movment increases. Body’s voluntary muscles are paralyzed to prevent taking any action from dreams. Dreams are more like emotional, detailed and memmorable that usually comes out from your subconsciuss mind.
After REM sleep, person again goes into the new sleep cycle.
How much sleep is recommended to a person?
For an normal adult 7 to 9 hours of sleep is enough. Small babies need more sleep. School children need sleep for 9 to 11 hours. Older adult should sleep for 7 to 8 hours.