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NSC 5404 : Session 3 Circadian Rhythms & Sleep Wake Cycles

NSC 5404 : Session 3 Circadian Rhythms & Sleep Wake Cycles. Leo Renaud, MD PhD Professor, Medicine & Neurology, University of Ottawa Associate Director & Senior Scientist, OHRI.

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NSC 5404 : Session 3 Circadian Rhythms & Sleep Wake Cycles

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  1. NSC 5404 : Session 3Circadian Rhythms & Sleep Wake Cycles Leo Renaud, MD PhD Professor, Medicine & Neurology, University of Ottawa Associate Director & Senior Scientist, OHRI

  2. Body rhythms: biological processes that show cyclical variation over time…range from hours to years…reflect the influence of the earth’s rotation upon us • Circadian rhythms • (circa= approx & diem =day) operate over 24 hrs e.g. sleep-wake cycle, body temp, plasma cortisol levels • Ultradian rhythms • (less than one day) e.g. stages of sleep (REM= Rapid Eye Movement, SWS= Slow Wave Sleep patterns) • Infradian rhythms • (more than one day) e.g. female menstrual cycle • Circannual rhythms • (yearly) e.g. hibernation patterns

  3. Research studies into Ultradian rhythms. • These are rhythmic cycles with a period of less than one day. Examples include levels of alertness throughout the day and the cycle of brain activity during sleep. • NREM and REM: There are four stages (1 & 2) which are shallow into deep sleep/slow wave sleep (3 & 4). These cycles continue throughout the night with (SWS) becoming shorter and REM becoming longer as the night progresses. Cycles last for approx 60 mins in early infancy and 90mins in adolescence. • The use of an electroencephalogram (EEG) can show the electrical activity of the brain. There are different patterns of activity at different times during sleep (Rechtschaffen & Kales, 1968).

  4. Research studies into Ultradian rhythms….

  5. Body rhythms: biological processes that show cyclical variation over time…range from hours to years…reflect the influence of the earth’s rotation upon us • Circadian rhythms • (circa= approx & diem =day) operate over 24 hrs e.g. sleep-wake cycle, body temp, plasma cortisol levels • Ultradian rhythms • (less than one day) e.g. stages of sleep (REM= Rapid Eye Movement, SWS= Slow Wave Sleep patterns) • Infradian rhythms • (more than one day) e.g. female menstrual cycle • Circannual rhythms • (yearly) e.g. hibernation patterns

  6. Circadian rhythms abound in mammals

  7. The role of Endogenous pacemakers & Exogenous Zeitgebers. • The main pacemaker for endogenous (internal) rhythms is the suprachiasmatic nucleus (SCN= above the optic chiasm. SCN receives information directly from the eye and the rhythm can be rest by the amount of light entering the eye…light is a powerful zeitgeber (trigger change in circadian rhythms)

  8. Suprachiasmatic nucleus (SCN)

  9. Circadian rhythms are generated by cells in the hypothalamic suprachiasmatic nucleus (SCN), location of THE biological clock in the mammalian brain

  10. Light-dark cycles and the clockLeft: actograms from intact, Cry-KO and SCN lesioned rodentsRight: Activity in a SNC cell over the day-nite cycles

  11. Circadian rhythms • Lacking zeitgbers (e.g. isolation) ~25 hr cycle • Entrained to solar day (light-dark cycle) • Influenced by environmental clues and endogenous factors (e.g. need to sleep) • Applications to the study of circadian rhythms: alertness (study, work, accidents); chronobiology & chronotherapeutics

  12. Should you get up in the morning?? Well, maybe not…why? Check the facts!

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