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Psychology (9,573)
PSYB64H3 (197)
Chapter 11

Chapter 11

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University of Toronto Scarborough
Janelle Leboutillier

Sleep and Waking CIRCADIAN RHYTHMS Circadian Rhythms a repeating cycle of about 24 hours Sleep follows the circadian rhythm To establish and maintain these rhythms internal biological clocks interact with stimuli known as zeitgeberslight is the most important zeitgeber external cue for setting biological rhytms for human beings In the absence of light human free running circadian rhythm non synched with environmental cues lasts 242249 hours Exposure to light resets or entrain the internal biological clock to the 24 hour cycle of the earths rotation Blind people and submarine people experience free running cycles that are longer than 24 hours and these result in severe sleep disruptions In addition to light other zeitgebers include physical activity feeding body temperature and sleep related hormones Variations in Sleep PatternsIndividual sleep patterns result from different versions of genes responsible for our internal clocks Morning peopleLarksNight peoplenight owlsmany fall somewhere between the two Nearly everyone acts like an owl during adolescencethis is because melatonin drops dramatically at the onset of puberty and contributes to age related changes in sleep habitsFollowing adolescence many temporary owls will revert to their previous state possibly due to maturation of neural systems that regulate sleepIn one case shifting school start time from 715 to 840 improved attendance and gradesShift Work Jet Lag and Daylight Saving TimeWhen work demands and circadian rhythms dont match shit gets fucked4080 of workers on the 11pm to 730am night shift experience disturbed sleep and a cluster of symptoms known as shift maladaption syndromethey obtained 15 hours less sleep which lead to frequent health personality mood and interpersonal problemsaccident rates in the 3pm1130pm shift are higher than in the traditional night shift and are even higher in the 11pm730am shift night shift workers more likely to develop breast cancerhospital workers more likely to make errors during night shifts than day shiftsConflicts between internal clocks and zeitgebers result in jet lagwhich is fatigue irritability and sleepiness resulting from travel across time zones the travel is not to blame chronic jet lag may have more serious consequences flight attendants who crossed time zones at least once a week for four or more years had reduced reaction times and made 9 more mistakes on memory tasks than local crews Because the freerunning cycle is more than 24 hours long people adjust more readily when travel or changes in shift work require us to stay up later and sleep laterAka its easier to adjust to a phasedelay set clock fartherof our cycle than to a phaseadvanceset clock earlierDaylight saving time offers another opportunity to observe our responses to phase shifts Fall shift is equivalent to westward travel and produces little disruption In contrast spring shift produces symptoms similar to jet lag for a day or twoThe phasedelay shift in fall resulted in a 7 decrease in traffic accidents and the phase advance spring resulted in a 7 INCREASEInternal ClocksThe bodys master clock is the suprachiasmatic nucleus SCN in the hypothalamus the name comes from the structures location above supra the optic chiasm Axons of special retinal ganglion cells known as nonimage forming NIF cells leave the optic nerve and project to the SCN forming the retinohypothalamic pathway Unlike other retinal ganglion cells the NIF cells do not process information about visual images they contain a photopigment known as melanopsinfor lightThe SCN is active only during the day same for nocturnal and diurnal and helps animals distinguish between day and night but other structures dictate whether an animal is nocturnal or diurnal in its behaviour SCN is not dependent on input from other structures to maintain its rhythms isolated SCN tissue cultures continue to show rhythmic fluctuations in activity consistent with the source animals previous daynight cycle Transplants of SCN tissue also support its role as a master internal clockits possible to breed hamsters with short free running cycles of about 20 hours normally 24When SCN tissue from a short period hamster is transplanted in a normal hamster the normal hamster shows short free running cycle and vice versa The SCN acts as a master clock that coordinates activities of other internal peripheral clocks that exist in most body cellscells from the SCN liver lung and muscle of rats were observed following a 6 hour phase shift in the rats lightdark schedules SCN adjusted to the new time after only one or two cycles of light and dark but peripheral clocks were much slower to respond Lung and muscle required 6 cycles and liver required 16 cyclesThe rhythms of SCN are heavily influenced by lightin contrast the peripheral clocks are more easily influenced by daily feeding cycles
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