How Do You Fall Asleep|Sleep Cycle.
When you fall asleep, the pattern of sleep is not uniform throughout. There are variations in the sleep patterns and these variations constitute the sleep cycle. These sleep variations also form the different stages of sleep and define how you fall asleep.
Each stage of sleep is different from each other in terms of what happens in the brain and body. Each part of the sleep has a different function to perform in preparing you for the next day and it is important that you spend appropriate sleeping hours in each stage of sleep.
Stages of Sleep.
EEG of sleep is not uniform throughout your sleep and it changes over the course of the night. It is these changes which help to chart out the various stages of sleep. Studies to know what happens when you fall asleep were conducted using the electroencephalogram and instruments which measured eye and muscle movements were used which revealed that there were two main stages of sleep. These stages were defined by the electric patterns in the brain and the presence and absence of eyeball movements. The two types of sleep are:
1) Non rapid eye movement (NREM) sleep is also called the quite sleep. This stage of sleep consists of four stages each being deeper than the previous one. N1, N2, N3 and the 4th stage of NREM sleep which is also known as the delta sleep or slow wave sleep. In NREM sleep, as the stages of sleep progress the brain waves become slower and more synchronized. These stages are described in detail in NREM sleep.
2) Rapid Eye Movement (REM) sleep is also called the active sleep or paradoxical sleep. This is the part of sleep when you actively dream and the eye balls move back and forth, which is why it is called rapid eye movement sleep. REM sleep is described in detail in REM sleep.
Picture showing stages of sleep.
Click on image to enlarge
Sleep Cycle.
The sleep cycle consists of the four stages of NREM sleep and the REM sleep. Each sleep cycle typically lasts for 90 to 110 minutes and then begins again. About four to six cycles are repeated over the night’s sleep. When you fall asleep, the sequence of the sleep stages in a sleep cycle are not in order and are explained below.
What Happens When You Fall Asleep.
Sleep does not occur in the sequence mentioned above. Sleep begins with stage one (N1) and progresses to stage N2, N3 and then to the stage of delta sleep. After this stage, N3 and then stage N2 (of 5 to 10 minutes) are repeated before onset of REM stage. After REM stage, the body returns to stage N2 sleep.
Scientists are not sure but speculate that this specific sequence of NREM sleep and REM sleep occurs to optimize the mental and physical recuperation and certain aspects of memory consolidation. The image below shows stage-wise what happens when you fall asleep.
Picture showing sleep cycle sequence.
Changing Sleep Patterns in Sleep Cycle.
Various factors influence shifting sleep patterns. They are
- Age.
- Amount of recent sleep or wakefulness.
- Other factors before sleep such as stress, exercise.
- Environmental conditions such as climate and light.
In an infant, sleep often begins with REM sleep and the sleep cycle is much shorter at 50 to 60 minutes.
Sleep history of an individual also can shift sleeping patterns. Missing of a night’s sleep, irregular sleeping routines and frequent disturbance of sleep patterns can alter the sequence of the sleep cycle.
Drugs too can alter the sleep cycle events. Alcohol taken before sleep tends to suppress the REM sleep early in the night. After it is metabolized late in the night, REM sleep tends to rebound.
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