Ultradian rhythms AO1

• Stages of sleep

  Psychologists have identified 5 DISTINCT stages of sleep that altogether span approximately 90-100 minutes (average 5 a night depending on how many hours sleep) throughout the night with different stages having different durations.

  Most of what we know about these stages comes from EEG recordings that show distinct patterns of brain activity at different sleep stages.
• Stage 1 - Alpha waves


  Hypnogogic state (experience of the transitional state from wakefulness to sleep). Light sleep, easily woken, muscle activity slows down, occasional muscle twitching.

  Brainwaves become more slower and more rhythmic – start with alpha waves and progress to theta waves.  NON REM
• Stage 2 - Theta waves

  Breathing and heart rate slows. Eye movement stops and brain waves become slower with only occasional bursts of rapid brain waves (called sleep spindles). EEG shows brain activity gets slower. NON REM
• Stage 3 and 4 - Delta waves

  Difficult to wake someone up in these stages. Muscles are totally relaxed (stage where you experience bed wetting and sleep walking). Stage 4 is the deepest (slow wave sleep) – heart rate and blood pressure are at their lowest. NON REM
• REM sleep

  REM – Rapid Eye Movement, brain waves mimic activity during the waking state. Most (but not all) dreaming occurs here, body is paralysed (to stop the person acting out in their dreams).
• Endogenous pacemakers and sleep cycle

  •EP controlling REM appears to be the locus coeruleus (LC) – patch of cells located in a brain structure called the pons) produces noradrenaline and acetylcholine

  •Destruction of LC causes REM to disappear

  •If neurons in a different part of the pons are restroyed REM remains but muscle paralysis in REM disappears – results in a cat moving around although its completely asleep

  •This may lie behind behavioural sleep disorder where human sleepers may act out their dreams
• Basic rest activity cycle (BRAC)

  A biological rhythm of waxing and waning alertness with a period of approximately 90 minutes in humans. Periods of alertness and periods of fatigue
• Patterns alter as we age

  •New-born - 16 hours’ sleep, 50% REM (patterns of REM are observed in foetuses).

  •3-year-old - 12 hours’ sleep, 25% REM.

  •Adult - 8 hours’ sleep, 22% REM.

  •70+- 6 hours’ sleep, 14% REM.

  •This changing pattern of REM has led researchers to believe one function of REM is the growth and repair of the brain - needed a lot when young and less as we age.