Biopsychology 4

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  • Biopsychology
    • Biological rhythms
      • Circadian rhythms- variations of 24 hours. Green- mammals have 100 bio circadian rhythms e.g. body temp, hormones production, sleep/wake cycle
        • Sleep wake cycle-endogenous pacemakers(internal factors0, exogenous zeitgebers (external timekeepers)
          • Free flowing bio clock studies (human ps)- spend time away from external zeitgebers e.g. light and circadian rhythms studied.Siffre-spent 6 months in cave alone away from natural light/dark cycles. Cycle first erratic, settled after 25 hours
          • Bio clock in hypothalamus, SCN, neurons have inbuilt circadian rhythmic firing pattern
        • Morgan- removed SCN from hamsters, sleep/wake cycled disappeared, restablished with SCN transplant, supported by Silver et al
        • Evaluation - Siffre indicates presence of endogenous pacemakers+highlights importance of exogenous zeitgebers in 24 hour cycle
          • Miles et al- man blind from birth, strong 24.9 circadian rhythm, had to use stimulants to keep 24 hour cycles- shows how useful light is in 24 hour patterns (light dominant zeitgeber)
          • Luce and Segall- light cues disregarded in place like artic circle, sleep 7 hours despite during summer sun doesn’t set
      • Infradian rhythms-longer than 24 hours e.g. menstruation
        • Endogenous pacemaker in pituitary gland, releases FSH and LH
        • Reinberg- woman lived i n mine for 9 months with lamp, menstrual cycle reduced from 28 to 25.7 days, took 18 months to go normal- exogenous zeitgebers
          • Menarche more likely to occur in winter, younger in girls in north or blind (inconsistencies- Lin et al- light shortens menstrual cycle)
        • Exogenous factors- McClintock- women who live/spend a lot of time together can synchronise menstrual cycles
          • External zeigebers- pheromones-like hormones by released into the air, not consciously detectable
          • Russell et al- wore pads under arms for 24 hours, rubber on upper lip of recipient women, repeated for 5 months, period dates recorded, after 5 months 4/5 women synchronise with donor
      • Ultradian rhythms- less than 24 hours e.g. slow wave/REM rhythms during sleep
    • Role of endogenous pacemakers and exogenous zeigebers
      • 1)Suprachiasmatic nucleus- small cluster of cells in hypothalamus, have inbuilt circadian rhythm
        • Rhythms adjusted by exogenous zeigebers LIGHT. SCN have info on light from optic nerve even when eyes shut.
          • Light penetrates eyelids, special photoreceptors in eyes pick up light signals, carried to SCN
          • If endogenous clock running slow, morning light automaticallyshifts clock ahead, puts rhythm in step with world outside
      • 2) pineal gland and melatonin
        • Pineal gland- coverts neurotransmitter serotonin into melatonin, induces sleep by inhibiting brain mechanisms,promotes wakefulness
        • Pineal- contains light sensitive cells, when level of light falls melatonin produced to make us sleepy. When light levels high- production of melatonin is inhibited and we wake up
      • Exogenous zeigebeter - light regulates sleep/wake cycle by altering melatonin in the body


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