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PSYCH 261 - Week 8 Textbook Notes (Modules 9.1-9.3)

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Daniel Smilek

Module 91 Rhythms of Waking and SleepingEndogenous CyclesAn animals readiness for a change in seasons depends on a combination of current stimuli and internal mechanismsEndogenous circanual rhythms last about a year o ex Bird preparing for flightEndogenous circadian rhythms last about a day o ex Urge to sleep depends partly on time of day not just how long youve been awake o Depending on the individual and the details of the procedure the selfgenerated cycle may be slightly longer or shorter than 24 hoursCircadian rhythms affect more than just the sleepwake cycle o Involved in eating drinking urination hormone secretion sensitivity to drugs body temperature moodCircadian rhythms generate a period close to 24 hoursZeitgeber timegiver the stimulus that resets the circadian rhythm o ex Light exercise arousal meals temperature of environment o Social stimuli are weak zeitbergers unless they induce vigorous activityBlind people need to reset circadian rhythms by zeitbergers other than light o Those who are not sufficiently sensitive to secondary zeitbergers produce circadian rhythms slightly longer than 24 hours which may lead to insomnia at night and sleepiness during the dayJet lag a disruption of circadian rhythms due to crossing time zones o Mismatch between internal circadian clock and external time o Going west we phasedelay our circadian rhythms going east we phaseadvance our circadian rhythms o Jet lag is often stressful increasing cortisol levels which may damage hippocampal neuronsWorking at night does not change circadian rhythm since artificial lighting is only moderately effective in resetting itMechanisms of the Biological ClockCurt Richter reported that the body generates its own rhythms and is insensitive to most forms of interference o Blinddeaf animals generate circadian rhythms but they are often out of phase with external worldDepends on suprachiasmatic nucleus SCNo Part of hypothalamus located above optic chiasm o Provides main control of circadian rhythms for sleep and body temperature o If SCN neurons are removed from the bodydisconnected from the brain they continue to produce circadian rhythm of action potentials o Interactions among cells sharpen accuracy of rhythm o In transplants rhythm follows pace of donors not recipients showing that they come from SCN itselfAxons from retinohypothalmic path of optic nerve alter SCN settings o Most input does not come from normal retinal receptors o Retinal ganglion cells with their own photopigment melanopsin respond directly to lightLocated near periphery not evenly throughout retinaRespond to light slowly and turn off slowly when light stopsRespond to overall average amount of light not to instantaneous changes
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