The Human Brain- 2

Stages of Sleep

After having reconciled and facing a tireless day, the most relaxing and essential phase of sleep is exorbitant. Regardless of the complete day cycle; we often misunderstand the phase of ‘sleep’ to be a long stretch complete one cycle. But how is it that we fall asleep? What changes does our brain undergo while falling asleep? Well here is an interesting fact that’s going to completely redefine ‘Sleep and stages of sleep’.

During the early 1950’s, with the help of an electroencephalograph; a young scientist named Eugene Aserinsky was able to demonstrate the different phases of sleep by the diversity and changes in brain waves. Accordingly, after further studies sleep can be defined under two categories namely:

  1. REM (Rapid eye movement also known as active sleep or paradoxical sleep)
  2. NREM (Non – rapid eye movement also known as quiet sleep).

Earlier the scientists divided the stages of sleep into ‘5 stages’; but after recent advancement, stages 3 and 4 were combined to form one stage and hence now the sleep is defined under 4 stages of sleep’.Regardless of the categories; the processes through sleep progresses is as follows:

The Beginning of sleep:

Initially, when we try to relax that is the state where we are relatively quite awake; our brain starts producing ‘Beta Waves’ that are short and fast. The more and more we get relaxed, the brain later then produce ‘Alpha Waves’. This phase when we are not quite asleep, we may feel certain strange illusion known as ‘hypnagogic hallucinations’. For instance, sometimes you may feel suddenly that you are being called by your name etc. defines this phenomenon. Also, sometimes suddenly you may feel startled; this phenomenon of facing ‘myoclonic jerks’ is also quite common in this phase.

Source: ishareimage

Source: ishareimage

STAGE 1 – This is relatively light stage of sleep and also can be termed to be the transition of a person from wakefulness and sleep. It is during this phase that the brain produces high magnitude ‘Theta waves’ that are short waves while attempting to relax. This phase may last for 5 – 15 minutes. This phase is a light phase and hence even when waken up; it is obvious that we weren’t quite asleep.

STAGE 2 – During this stage the brain starts producing slow, rhythmic ‘sleep spindles’. This phase lasts up to 20 minutes. It is during this phase that the heart beat slows down and the body temperature is found to decrease slowly.

STAGE 3 – This stage is also termed as ‘delta sleep’ since brain starts emitting slow brain waves that are called as ‘delta waves’. This stage marks the transition between light sleep and deep sleep. Earlier this stage was been divided into stage 3 and stage 4. During this stage, we become less responsive towards the environment and nearby activities. Sleepwalking is most likely a phenomenon resulting during this stage.

STAGE 4 – This stage is termed under REM. This stage is characterized under rapid movement of eye and increased brain activity. During this stage, there is increase in the brain activity but at the same time; muscle relaxation takes place. It is during this stage that we tend to dream and hence this stage is also known as ‘paradoxical sleep’ since even though the brain activities increase but at the same time the voluntary muscles also get paralyzed.

Even though the sleep is defined under these 4 stages, but the sleep doesn’t proceed in a sequential manner that is Sleep begins in stage 1 and progresses into stages 2, and 3. After stage 3 sleep, stage 2 sleep is repeated before entering REM sleep. Once REM sleep is over, the body usually returns to stage 2 sleep. Sleep cycles through these stages approximately four or five times throughout the night. On average, we enter the REM stage approximately 90 minutes after falling asleep. The first cycle of REM sleep might last only a short amount of time, but each cycle becomes longer. REM sleep can last up to an hour as sleep progresses.

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