PSYB64H3 Quiz: Quiz 2 Notes

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17 Dec 2017
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Circadian rhythm: a repeating cycle of about 24h. Ultraradian cycle: a cycle that occurs several times in a single day: reg cycles of relative activation and quiet occur every 90-120 mins in a 24h day example of an ultraradian cycle. Zeitgeber: an external cue for setting biological rhythms. Light is the most imp zeitgeber for humans. Free-running circadian rhythm: a rhythm that is not synchronized to environmental time cues. Without nat light, human free-running circadian rhythms last about 24. 2- Entrainment: the resetting of internal biological clocks to the 24h cycle of the earth"s rotation. Totally blind people and sailors on submarines experience free-running cycles that are longer than 24h, often resulting in severe sleep disruptions. When food is plentiful, light has the greatest impact on circadian rhythms, but when food is scarce, animals remain awake when food is available regardless of lighting conditions. Rem cycles appear approx. every 90-120 mins during sleep.