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  2. Ultradian rhythm - Wikipedia

    en.wikipedia.org/wiki/Ultradian_rhythm

    In contrast, circadian rhythms complete one cycle daily, while infradian rhythms such as the menstrual cycle have periods longer than a day. The Oxford English Dictionary's definition of Ultradian specifies that it refers to cycles with a period shorter than a day but longer than an hour. [1]

  3. Basic rest–activity cycle - Wikipedia

    en.wikipedia.org/wiki/Basic_rest–activity_cycle

    Empirically, it is an ultradian rhythm of approximately 90 minutes (80–120 minutes [2]) characterized by different levels of excitement and rest. The cycle is mediated by the human biological clock .

  4. Sleep cycle - Wikipedia

    en.wikipedia.org/wiki/Sleep_cycle

    Kleitman and others following have referred to this rhythm as the basic rest–activity cycle, of which the "sleep cycle" would be a manifestation. [ 14 ] [ 19 ] A difficulty for this theory is the fact that a long non-REM phase almost always precedes REM, regardless of when in the cycle a person falls asleep.

  5. What is a siesta? The history of the afternoon nap and its ...

    www.aol.com/lifestyle/siesta-history-afternoon...

    "The word 'siesta' comes from the Latin 'sexta,' meaning the sixth hour after someone wakes up," says Dr ... but a siesta is particularly effective because it aligns with natural circadian rhythms ...

  6. Zeitgeber - Wikipedia

    en.wikipedia.org/wiki/Zeitgeber

    A zeitgeber (/ ˈ (t) s aɪ t ɡ eɪ b ər, ˈ z aɪ t-/ (T)SYTE-gay-bər, ZYTE-, German: [ˈtsaɪtˌɡeːbɐ]) is any external or environmental cue that entrains or synchronizes an organism's biological rhythms, usually naturally occurring and serving to entrain to the Earth's 24-hour light/dark and 12-month cycles.

  7. Chronobiology - Wikipedia

    en.wikipedia.org/wiki/Chronobiology

    The best studied rhythm in chronobiology is the circadian rhythm, a roughly 24-hour cycle shown by physiological processes in all these organisms. The term circadian comes from the Latin circa, meaning "around" and dies, "day", meaning "approximately a day." It is regulated by circadian clocks.

  8. Human brain - Wikipedia

    en.wikipedia.org/wiki/Human_brain

    The circadian rhythm is controlled by two main cell groups in the hypothalamus. The anterior hypothalamus includes the suprachiasmatic nucleus and the ventrolateral preoptic nucleus which through gene expression cycles, generates a roughly 24 hour circadian clock. In the circadian day an ultradian rhythm takes control of the sleeping pattern.

  9. Biological rhythm - Wikipedia

    en.wikipedia.org/wiki/Biological_rhythm

    Ultradian rhythms, which are cycles shorter than 24 hours, such as the 90-minute REM cycle, the 4-hour nasal cycle, or the 3-hour cycle of growth hormone production. Tidal rhythms, commonly observed in marine life, which follow the roughly 12.4-hour transition from high to low tide and back. Lunar rhythms, which follow the lunar month (29.5 ...