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Chapter 11

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University of Toronto Scarborough
Janelle Leboutillier

PSYB64Chapter 11 Sleep and WakingCircadian RhythmsThe interplay between sleep and waking cycles follows circadian daily rhythmsTo maintain these biological rhythms internal biological clocks interact with stimuli called zeitgebers o Light is the most important zeitgeber for human beings o In the absence of natural light human free running circadian rhythms last about 242 hours to 249 hours o Exposure to sunlight helps resetor entrain the internal biological clock to the 24hour cycle of the earths rotationTotally blind people and sailors on submarines experience freerunning cycles that are longer than 24 hours often resulting in severe sleep disruptionsOther zeitgebers include physical activity feeding body temperature and sleeprelated hormones Variations in Sleep PatternsPeople who are most alert and productive in the morning have been referred to as larks whereas night people have been referred to as night owlsNearly everyone acts like an owl during adolescenceMelatonin one of the neurochemicals involved in sleep regulation drops dramatically at the onset of puberty contributing to agerelated changes in sleep habitsFollowing adolescence many temporary owls will revert to their previous state possibly due to the maturation of neural systems that regulate sleepShifting from a 715am start time to an 840am start time improved attendance and student grades at Minnesota high schoolsShift Work Jet Lag and Daylight Saving TimeBetween 4080 workers on the 1100pm to 730am night shift experience disturbed sleep and a cluster of symptoms called shift maladaptation syndrome which can lead to frequent health personality mood and interpersonal problems Accident rates in the 300pm to 1130pm shift are higher than in the traditional day shift and higher still during the 1100pm to 730am Night shift workers are more likely than other workers to develop breast cancerHospital workers such as nurses are more likely to make significant errors during the evening or night shifts than during day shiftsConflicts between internal clocks and external zeitgebers also result in the unsettling experience of jet lagAirline flight attendants who crossed the time zones at least once a week for 4 years or more had reduced reaction times and made 9 more mistakes on memory tasks than local crews who didnt cross time zones Because the human free running 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 latero It is easier to adjust to a phase delay of our cycle setting the clock to a later point than to a phaseadvance setting the clock to an earlier point Internal ClocksThe bodys internal master clock is the suprachiasmatic nucleus SCN in the hypothalamusAxons of special retinal ganglion cells nonimagine forming cells NIF contain a pigment called melanopsinThe SCN is active only during the day regardless of whether a species is diurnal or nocturnal The SCN helps animals distinguish between day and night but other structures dictate whether an animal is nocturnal or diurnal in its behaviorThe SCN is not dependent on input from other structures to maintain its rhythmso Isolated SCN tissue cultures continued to show rhythmic fluctuations in activity consistent with the source of animals previous daynight cycleWhen SCN tissue from a shortperiod hamster is transplanted into a normal hamster the normal hamster shows the short freerunning cycle o When SCN tissue from a normal hamster is transplanted into a shortperiod hamster the hamster shows normal 24hour cycleso In both cases the behavior of the transplant recipient matches the behavior of the donorThe SCN acts as a master clock that coordinates the activities of other internal peripheral clocks that exist in most body cellsThe rhythms of the SCN are heavily influenced by the presence of lightThe peripheral clocks are more easily influenced by daily feeding cyclesAbrupt changes in feeding patterns during the day only can reset the animals circadian rhythms by influencing these peripheral clocks Many travelers attempt to compensate for jet lag by immediately adjusting their mealtimes to their current time zonesThe Cellular Basis for Circadian RhythmsThe SCN can tell time due to the oscillation of protein production and degradation within a cellResearch with fruit flies allowed researchers to identify 3 separate genes and their protein products that are involved with their cellular circadian rhythmso Per period o Tim timeless o Clock circadian locomotor output cycles kaputPer and tim proteins inhibit the clock protein whereas clock protein promotes the production of more per and tim proteinsAs levels of per and tim proteins increase inhibition of clock protein ensures that no further per and tim proteins will be produced o As levels of per and tim proteins drop over time the reduced inhibition of the clock protein results in increased production of more per and tim proteinsBiochemistry and Circadian RhythmsThe SCN both regulates and responds to melatonin an indolamine secreted by the pineal glandMelatonin levels are very low during the day begin to rise in the hours before sleep and usually peek at about 400am when everyone feels really sleepyTotally blind people experience a melatonin peak at different times each day leading to sleep difficultiesPeople with pineal gland tumors or other medical conditions affecting melatonin report sleeping problems
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