Sleep and Dreams

Sleep - short definition

It is a state of rest which affects both body and mind, where we are unconscious. In a healthy person, this follows a circadian rhythm (ie a daily cycle).


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Dreams - short definition

These are the images and emotions created by the unconscious mind during sleep.

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Why do we sleep ?

  • Inactivity theory states that organisms have evolved sleep in order to protect themselves during periods that they would be vulnerable to predators. For example, people tend to sleep during hours of darkness.
  • Energy conservation theory states that organisms sleep in order to cut the amount of energy being used.
  • Restoration theory states that the point of sleep is to allow the body to repair and restore itself. According to Oswald (1966), REM sleep restores the brain and NREM sleep restores the body.
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Non REM sleep - stage 1

  • is the beginning of the sleep cycle
  • is a light stage of sleep
  • is a transition period between wakefulness and sleep
  • the brain produces very slow brain waves, the theta waves
  • it lasts only for a brief time
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Non REM sleep - stage 2

  • it lasts for about 20 min
  • the brain begins to produce rapid, rythmic waves known as sleep spindles
  • body temperature starts to decrease
  • heart rate begins to slow
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Non REM sleep - stage 3


  • brain produces deep, slow waves known as delta waves
  • is a transition period between light sleep and deep sleep
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Non REM sleep - stage 4

  • is a deep sleep
  • it lasts for about 30 min
  • bed-wetting and sleepwalking are most likely to occur at the end of this stage
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REM sleep - Stage 5

  • stage 5 is known as rapid eye movement sleep (REM sleep)
  • there are around 3-5 REM episodes a night (occupies 20-25% of total sleep in adults)
  • most dreaming occurs during this stage of sleep
  • increased respiration rate
  • increaced brain activity
  • muscles become more relaxed
  • is also referred to as paradoxical sleep
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1. Describe REM sleep and Non-REM sleep.

2. After REM sleep is over, what usually happens to theh body?

3. After thinking about the different stages of sleep, what effects might sleep deprivation have on someone?

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