NREM stages

• NREM Stage one


  We drift in and out of a true sleep state - we lose awareness of ourselves and surroundings (can sometimes be aware of faint sounds in the background)
• Physiological changes in NREM Stage one

  • Lower level of body arousal - decrease in heart rate, respiration, body temperature and muscle tension
• Hypnic jerk


  A jerky sensation experienced as muscles are relaxing
• EEG pattern in NREM Stage one

  Decrease in alpha wave production as they are replaced by theta waves
• Duration of NREM Stage one

  • Typically lasts for 5-10 minutes, can be as little as thirty seconds or up to ten minutes
• If people are woken up during NREM Stage one they may feel as if they had not slept at all
• NREM Stage two


  A light stage of sleep where the person is truly asleep
• NREM Stage two


  • Less easily disturbed than stage one
  • Can still be aroused from sleep
• NREM Stage two

  1. Lasts for about 10-20 minutes

  2. Body movements lessen

  3. Breathing becomes more regular

  4. Blood pressure lowers

  5. Body tempo falls

  6. Heart rate is slower
• Brain waves in NREM Stage two

  • Mainly theta waves
  • Slightly lower in frequency and higher in amplitude than stage one
• Sleep spindles


  Bursts of high frequency brain wave activity that last for about one second and indicate the person is truly asleep
• The brain in NREM Stage two

  Still responds to external and internal stimuli (e.g. knock on the door, muscle tension)
• EEG pattern in NREM Stage two

  • Burst of low frequency and slightly higher amplitude waves called k complexes in response to arousing stimuli, showing sleep has become much deeper
• In comparison to stage 3 and 4, stage 2 is still considered to be light sleep
• If someone is woken during NREM Stage two, they would say they were not asleep, just dozing
• NREM Stage three

  Start of the deepest period of sleep
• NREM Stage three

  • Lasts for about 10 minutes
  • Known as moderately deep sleep
  • Heart rate, blood pressure and body temperature continue to drop
  • Breathing rate continues to be slow and steady
  • Individual is extremely relaxed and becomes less responsive to the outside world
  • Difficult to arouse, and when woken are groggy and disorientated
• EEG in NREM Stage three

  1. Brain's electrical activity is reduced

  2. Delta waves begin to appear

  3. Delta waves make up 20-50% of the brain waves recorded

  4. Delta waves are slow, large and regular

  5. Delta waves are lower in frequency and higher in amplitude than alphas and thetas
• Slow wave sleep (SWS)


  Begins within an hour of falling asleep<|>Lasts for about 30 minutes
• NREM Stage four

  When more than 50% of the brain activity consists of delta waves on an EEG then the person has entered in to stage 4 which is the deepest sleep and they will be extremely difficult to rouse
• Very deep sleep


  The sleep in NREM stage 4
• Psychological signs of NREM stage 4

  • Muscles are completely relaxed and we barely move
• Delta waves in NREM stage 4

  Dominate the EEG pattern, but they are even slower and larger than in stage 3
• Waking up from NREM stage 4

  • Takes up to 10 minutes to orient themselves, and they have poor memory of sleep events - referred to as sleep drunkenness - or better known to psychologists as sleep inertia
• Duration of NREM stage 4 sleep

  In the first sleep cycle, a person may spend 20 minutes in stage 4, however, as the night progresses, less and less time is spent in stages 3 and 4. In sleep cycles close to the morning, there may be no stage 3 or 4 sleep at all.
• Sleep before midnight is the best sleep because it may be the most rejuvenating and beneficial sleep
• People deprived of stage 4 sleep often complain about muscle aches and tension
• It is during the very deep sleep stages 3 and 4 that sleep phenomena such as sleep walking, sleep talking, night terrors and bed wetting occur
• REM sleep

  REM is a period of rapid eye movement sleep during which the eyeballs rapidly move beneath closed eyelids, darting back and forth and up and down in a jerky movement

  The brainwave pattern associated with REM sleep is irregular, consisting of low amplitude, relatively high - frequency beta waves, like those produces in alert wakefulness.

  The body’s internal functioning is more active during this sleep compared to NREM sleep, the heart rate is faster and more irregular blood pressure rises, breathing is quicker and more irregular, however, the sleeper is totally relaxed.
• Approximately 80% of our sleep time is spent in NREM
• Typically the first half of the night has more NREM sleep than the second half of the night
• NREM sleep

  Consists of 4 stages in which the sleeper progresses from a stable of light sleep to the stage of deepest sleep and back again through one or more stages to light sleep
• During NREM the brain is active, but not as active as during REM sleep
• Stages of sleep

  • Each stage is dominated by a particular identifiable brain wave pattern/rhythm that is different from that of the other stages
  • Each brain wave can be distinguished in terms of two characteristics: the number of brain waves and the intensity of the brain waves
• Frequency


  Describes the number of brain waves
• Amplitude

  Describes the intensity of the brain waves (estimated by the size of the brain waves - peaks and troughs)
• When we first close our eyes and begin to relax before going to sleep we have a burst of alpha waves
• Alpha waves

  Associated with relaxation and drowsiness - the pattern is relatively high frequency and medium amplitude waves
• Hypnagogic state

  The transition period from being awake to being asleep characterised by slow, rolling eye movements for a minute or two
• Some people experience flashes of light or colour, feelings of floating and weightlessness, dreamlike images, jerky movements or a sense of falling or slipping during the hypnagogic state