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Lecture 21 - Circadian Rhythms & Learning

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Michelle French

L21 Nov 02 11Circadian RhythmsLearningCircadian RhythmsGoverned by neuronal oscillator w near24 h periodentrained to exact daynight cycle by retinal input from ganglion cells w melanopsinretinal projection to 1 suprachiasmatic nucleus in hypothal or to 2 pretectal area pupilary light reflex sym efferentssup cervical ganglionpineal bodyCircadian ModulationHormone synthesissecretionfluctuation ex Steroids triggered by ATCH production w stress axismaximal production when wake uposcillator made up of transcriptiontranslation body templowest in morning when asleepprocessesautonomic bhvrs eg feedingcertain prots made in daylight others at nightmoodinput of melanopsin from retinasync w alertnessdaynight cyclesleepwake cycle but oscillator takes 24hrs anyway so dont need retinal for 24hr oscillationPineal Bodyactivated via sym system in darkness cf pupillary light reflexsecretes melatonin right into bloodstream blocked by even small amts of light esp bluegreentarget neurons ex In superchiasmic nmelatonin involved in sleep induction enhances to deeper sleep not actually necessary but promotesmaximal secretion at about 2 amperiod of deep sleepmaster clock regulating circadian rhythms in higher secretion in summer much shorter superchiasmic n in hypothal on top of optic nights so compensates w more melatonin chiasm short distance for melanopsin to project than winterrdon either side of 3 ventricletrue in mammals who operate on traditional most active during day when melanopsin daylight hours but not for humans since maximally responds to lighthave artificial lightproduction of melatonin for uniform over the yearconseq 24hr oscillatormaybe harder to adapt seasonally to changesBased on gene transcriptiontranslation genesprot product interactions form ve feedback loop takes a long time almost 24hrs internal metabolic movementproduces oscillation regardless of retinal inputmechanism located in suprachiasmatic n of hypothal master circadian clockmodulated by 1 retinal input keeps in sync 2 pineal input eg adjust for seasonal variations more longterm 3 reticular activating systems serotonin
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