Detailed Notes on Sleep Stages

Stages of Sleep Monitored by EEG Patterns

Stage W (Wakefulness)

  • Definition: The state of being awake.
  • EEG Patterns:
    • Beta Waves:
    • High frequency, low amplitude.
    • Reflect concentration and alertness.
    • More desynchronous compared to other brain waves due to varied sensory input.
    • Alpha Waves:
    • Present when relaxed but awake, indicating drowsiness or meditation.
    • Slower in frequency and higher in amplitude compared to beta waves, more synchronous pattern.

Stage N1 (Non-REM Sleep 1)

  • Definition: The first stage of non-REM sleep; the transition from wakefulness to sleep.
  • Characteristics:
    • Drowsy sleep with sudden muscle movements (myoclonic or hypnic jerks).
    • EEG Patterns:
    • Theta Waves:
      • Slower frequency, greater amplitude than alpha waves.
      • Transitioning gradually from relaxed state to sleep.

Stage N2 (Non-REM Sleep 2)

  • Definition: Light sleep stage following N1.
  • Characteristics:
    • Decreased muscle activity, less awareness of environment.
    • EEG Patterns:
    • Continued presence of theta waves.
    • Sleep Spindles:
      • Sudden bursts of high-frequency waves, characteristic of N2 sleep.
    • Sleep felt as less significant if awakened at this stage.

Stage N3 (Non-REM Sleep 3)

  • Definition: The deepest stage of sleep; slow wave sleep.
  • Characteristics:
    • Characterized by delta waves, which are the slowest and highest amplitude brain waves.
    • Important for restorative functions; bedwetting, sleepwalking, and sleep talking may occur here.
    • Individuals are often confused and disoriented if awakened.

Stage R (REM Sleep)

  • Definition: Rapid eye movement sleep; an active stage of sleep where dreaming occurs.
  • Characteristics:
    • Fast EEG waves similar to those of relaxed wakefulness.
    • Eyeballs move rapidly; dreams are more vivid and emotionally charged.
    • Reports of dreaming occur more frequently compared to non-REM sleep and are generally longer and less relevant to waking life experiences.

Sleep Cycle

  • Duration: Each sleep cycle lasts about 90 to 100 minutes and repeats several times throughout the night.
  • Distribution:
    • About 60% of sleep in light sleep (N1 and N2), 20% in slow wave sleep (N3), and 20% in REM sleep.
  • Pattern:
    • More deep sleep (N3) occurs in the first half of the night, with REM sleep periods lengthening towards morning.
    • First REM period lasts around 10 minutes while the last can last up to an hour.

Neurotransmitters and Sleep

  • Roles of Neurotransmitters:
    • Serotonin, Norepinephrine, Acetylcholine: Key neurotransmitters involved in sleep regulation.
    • Levels drop as sleep begins, reaching their lowest in N3.
    • REM sleep is activated by an increase in acetylcholine, which stimulates the cerebral cortex while other brain areas are relatively inactive.
    • Sleep cycles may end naturally at the conclusion of REM, following a rise in serotonin and norepinephrine, facilitating a gradual transition to wakefulness.