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Sleep definitions

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  • Circadian Rhythm
    Approximately 24-hour cycle regulating sleep and wakefulness, influenced by light and internal cues.
  • Suprachiasmatic Nucleus
    Hypothalamic structure receiving light signals, coordinating timing of sleep and wake cycles.
  • Pineal Gland
    Small endocrine gland releasing melatonin in response to signals from the brain to promote drowsiness.
  • Melatonin
    Hormone increasing drowsiness, released in darkness to help initiate sleep.
  • Sleep Cycle
    Repeated pattern of NREM and REM stages, lasting 90–120 minutes, occurring multiple times nightly.
  • REM Sleep
    Sleep phase with rapid eye movement, vivid dreaming, muscle paralysis, and brain activity resembling wakefulness.
  • NREM Sleep
    Non-rapid eye movement sleep, divided into four stages, featuring progressively deeper sleep and slower brain waves.
  • Electroencephalogram
    Device recording electrical brain activity, used to distinguish sleep stages by wave patterns.
  • Beta Waves
    High-frequency, low-amplitude brain activity seen during wakefulness and REM sleep.
  • Theta Waves
    Lower-frequency brain activity marking light sleep, especially stage 1.
  • Sleep Spindles
    Brief bursts of very high-frequency brain activity, characteristic of stage 2 sleep.
  • K-Complexes
    Sudden, high-amplitude EEG spikes, unique to stage 2 sleep.
  • Delta Waves
    Very high-amplitude, low-frequency brain activity, dominant in deep sleep stages 3 and 4.
  • Amplitude
    Height of EEG waves, indicating strength of brain activity during different sleep stages.
  • Frequency
    Number of EEG wave cycles per second, used to differentiate sleep and wake states.