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PSYC388 BIOLOGICAL RHYTHMS AND SLEEP > MODULE 3: ENTRAINMENT BY LIGHT > Flashcards

MODULE 3: ENTRAINMENT BY LIGHT Flashcards

1
Q

what 3 words can describe the mechanisms responsible for circadian rhythms?

A

oscillator
pacemaker
clock

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2
Q

why is it important to know the subtle distinctions between the words oscillator, pacemaker, and clock?

A

multicellular organisms have circadian time systems with many, different, and sometimes hierarchical roles

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3
Q

define an oscillator

A

any device that produces a rhythm

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4
Q

why can oscillators be categorized along the range of slave to master?

A

they may be incapable of keeping a rhythm alone and or depend on signals from a pacemaker

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5
Q

what are secondary/local oscillators?

A

the position of the oscillator in a complex multi-oscillator system

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6
Q

where might someone find a seocndary/local oscillator?

A

a specific body tissue/organ or brain region

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7
Q

what is the role of a secondary oscillator?

A

inducing circadian rhythms on a particular region

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8
Q

if someone were to remove a secondary oscillator, what would happen?

A

the rhythmicity of the organ/tissue or region would be affected

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9
Q

what is a pacemaker?

A

the master oscillator that controls the other timing of other oscillators and direct processes

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10
Q

if a pacemaker is to be removed, what would happen?

A

the whole oragnism’s rhythms would be affected

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11
Q

true or false: removing a pacemaker would only result in local oscillators to stop

why?

A

false: they may continue but would desynchronize

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12
Q

what do pacemakers use to coordinate rhythms?

A

cycles of nature

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13
Q

what happens when an oscillator is synchronized to the external world?

A

a specific phase of the oscillator corresponds to a particular time of day

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14
Q

define a clock

A

a device that allows us to know the time of day even without knowing the sun’s position

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15
Q

what is an interval timer?

A

device that can time one cycle, stops and needs to be reset

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16
Q

what are 2 examples of interval timers?

A

hour glass and stopwatch

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17
Q

what are the 3 defining characteristics of circadian clocks?

A
  1. they are self-sustaining and persist with a 24 hour periodicity in constant conditions
  2. they are temperature compensated
  3. they are entrainable by environmental stimuli
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18
Q

circadian clocks ___ behaviour and physiology with predictable daily events in the real world

A

coordinate

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19
Q

when a circadian clock triggers a behaviour or physiological process with predictable events in the real world, they are analogous to what?

A

alarm clocks

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20
Q

when circadian clocks are being consulted continuously to allow memory/recognition each phase of their internal clock, what are they analogous to?

A

wrist watches

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21
Q

what are circadian clocks measuring when they permit species to organize their behavior/physiological processes into annual rhythms?

A

day length or photoperiodism

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22
Q

using circadian clocks to measure photoperiodism requires what?

A

a stable relationship with the solar day

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23
Q

what would happen if a clock is not synchronized with the light/dark cycle?

A

a particular phase would not be predictive of the local environment time

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24
Q

what 2 problems does entrainment need to solve?

A
  1. circadian clocks cycle with a periodicity that only approximates 24hrs
  2. must ensure that organisms do the right thing at the right time of day
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25
Q

describe how entrainment would address the approximation of 24hrs problem

A

must adjust the clock on a regular basis so it does not drift out of synchrony with the outside world

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26
Q

describe how entrainment would address the problem of matching an organism’s actions to a time of day

A

synchronizing to the outside world allowing for sleep and waking states to occur at the appropriate time

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27
Q

in diurnal animals, what is their dominant sense that helps with entrainment?

A

vision

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28
Q

what is the objective of entrainment?

A

control both period and phase of the circadian clock to align it with the environment

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29
Q

define zeitgeber

A

an external stimulus that can entrain a circadian clock

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30
Q

what is masking?

A

the direct effect of an environmental stimulus on a behavioural state

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31
Q

in diurnal animals ___ promotes alertness and ___ promotes sleep

A

light; dark

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32
Q

why do chronobiologists say the direct effect of light is considered masking?

A

light can mask the true phase of the circadian clock

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33
Q

what is negative masking?

A

when the environmental stimulus suppresses a behaviour that would normally be present during that time of day

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34
Q

what is positive masking?

A

when an environmental stimulus stimulates behaviour that would normally be absent during that time of day

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35
Q

what is the consequence of direct effect of light/dark on an animal’s behaviour who has no functional circadian clock?

A

a light-dark cycle could induce a daily rest-activity rhythm

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36
Q

what might be a reason that an animal may appear to be entrained by light/dark despite lacking any internal clock susceptible to entrainment?

A

a brain lesion or gene mutation

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37
Q

how can someone determine if an observed synchrony of a rest-activity cycle with light/dark is due to entrainment, masking, or both?

A

looking at how fast the rhythm synchronizes with the light/dark cycle

38
Q

if the synchronization to the LD cycle is instantaneous, what is it mostly likely due to?

A

masking

39
Q

how might someone investigate if a synchronization is due to masking or entrainment?

A

replace the light dark cycle with a constant condition and compare the timing of the activity onset between the first day of constant conditions and the last day of LD cycle

40
Q

what is the hypothesis that supports the mechanism of entrainment?

A

if 24hr LD cycles can entrain circadian rhythms that differ from 24hrs, the light and dark must shift or reset the that circadian clock to correct its phase each day or adjust the periodicity to make it equal to 24hrs

41
Q

what happens when light is introduced to a nocturnal animal during early subjective night?

A

cycle would be delayed and activity would begin later the next day in constant dark

42
Q

what happens when light is introduced to a nocturnal animal during late subjective night?

A

cycle would advance and begin earlier the next day in constant dark

43
Q

describe the difference between a phase response curve and dose-response curve

A

the x-axis plots the circadian phase at which the stimulus was administrated

44
Q

what is a point phase?

A

when the light is being presented at a particular point in the organism’s circadian cycle

45
Q

what is a phase shift?

A

when a phase of a circadian cycle is shifted after being introduced to a light pulse

46
Q

true or false: a light pulse shifts only one phase in a cycle

A

false: shifts all of the phases in a cycle together

47
Q

circadian hours are ___/24th of a full circadian cycle

A

1

48
Q

if an organism’s tau is 25 hours, what is one circadian hour for that organism?

A

25/24 = 1.04

49
Q

when studying nocturnal animals the beginning of subjective night is ____ and subjective day is ___

A

CT12

CT0

50
Q

a light pulse in early half of subjective night causes a ___?

A

phase delay shift

51
Q

a light pulse in the later half of the subjective night causes a___?

A

phase advance shift

52
Q

true or false: general features of PRC shape are universal to circadian clocks in all creatures

A

true

53
Q

describe how the PRC to light pulses suggests that entrainment to a daily light/dark cycle can be achieved by what?

A

adjusting the circadian clock phase each day in response to light at dawn or dusk

54
Q

what is a phase in a circadian cycle?

A

position of the oscillator within its cycle

55
Q

what is a parameter of a circadian cycle?

A

period or amplitude that can be set to a particular value which then defines a rhythm

56
Q

can a phase be a parameter?

A

no, it cannot be set to a permanent value

57
Q

what is the non-parametric model of entrainment?

A

hypothesis that entrainment can be achieved by small daily phase adjustments

58
Q

why is it called a non-parametric model?

A

the thing being adjusted is not a parameter of the clock

59
Q

what is the discrete entrainment mofdel?

A

light has a discrete/time-limited action on the clock as opposed to the continuous action of light

60
Q

what are the 3 properties of entrainment to LD cycles that can be predicted when one knows tau of a circadian clock and the shape of the phase response curve to light pulses

A
  1. limits to entrainment
  2. phase of entrainment
  3. gradual re-entrainment
61
Q

what are limits to entrainment?

A

circadian rhythms will only entrain to to LD cycles that have a period relatively close to 24 hours

62
Q

if a clock can only be shifted by 1/2 hours at most in a cycle then what happens when an LD cycle requiring a daily phase shift larger than that?

A

it won’t entrain

63
Q

what is the phase of entrainment?

A

the period of the clock should determine the timing of circadian rhythms when they are stably entrained to the LD

64
Q

what is gradual re–entrainment?

A

when a LD cycle is shifted, the circadian clock should re-train gradually over several days instead of instantly

65
Q

what is relative coordination/entrainment?

A

light affecting the clock by alternately delaying or advancing it but not enough to offset the difference between T and tau

66
Q

what are T-cycle experiments?

A

when the period of Zeitgeber is being manipulated

67
Q

what does the phase of entrainment depend on?

A

the difference between the period of the circadian clock and of the LD cycle

68
Q

what is the aftereffect of entrainment?

A

an indicator that the circadian clock has the capacity to adapt to the outside world even though they are genetically determined

69
Q

does a shift in the LD cycle result in a gradual or immediate re-entrainment?

A

gradual

70
Q

what indicates that the circadian clock can shift by only a certain amount in one cycle?

A

the light pulse in a phase-response curve

71
Q

what are the 4 main factors that determine the length of time it takes to fully shift to a new time zone?

A
  1. magnitude if the shift
  2. direction of travel
  3. timing of light exposure
  4. parameters of light stimulus
72
Q

in regards to the magnitude of a LD cycle shift: if it is a large shift that is required, will it take longer or shorter to re-entrain?

A

longer

73
Q

which way would someone fly to be able to re-entrain rapidly?

A

west

74
Q

which way would someone fly to be able to re-entrain more slowly?

A

east

75
Q

what would accelerate re-entrainment?

A

the right timing of light exposure

76
Q

what are the complementary factors of light exposure timing?

A

travel direction

the shift being delayed or advanced

77
Q

what are the 2 parameters of light stimulus?

A

amplitude and wavelength

78
Q

the brighter the light, the ___ the shift

A

greater

79
Q

which colour light is the most effective kind of stimulus?

A

blue light

80
Q

at what 2 times to nocturnal animals need light exposure to exhibit stable synchrony?

A

dawn and dusk

81
Q

what can induce phase shifts without altering the wavelength/amplitude but will alter the period?

A

light pulses

82
Q

what is the parametric entrainment model?

A

hypothesizes that light entrains circadian rhythms by altering both the phase and the period of the clock

83
Q

is the period of a clock a parameter?

A

yes

84
Q

what are the 3 experiments that observed parametric effects of light?

A
  1. tau in constant light/dark
  2. tau changing after light pulses
  3. aftereffects of entrainment on tau
85
Q

what was observed in tau in constant conditions for nocturnal and diurnal animals?

A

nocturnal: constant light slows/increases cycle length
diurnal: light exposure can lengthen or shorten the cycle to help it match the LD period

86
Q

what was observed of tau after light pulse application? (2)

A
  1. light pulses cause a change in phase shift and tau

2. light pulses that delay a clock lengthen a cycle and light pulses that advance a clock shorten a cycle

87
Q

what is an aftereffect of entrainment on tau?

A

LD cycle can alter the rate at which the clock oscillates (closer to frequency of the entraining LD cycle)

88
Q

when is entrainment most stable?

A

when light affects both phase and period

89
Q

what is entrainment in nature most likely due to?

A

both non-parametric and parametric effects

90
Q

why is studying entrainment difficult?

A

one must track both the activity rhythms and the actual light exposure to animal habitats

91
Q

what is biotelemetry?

A

the use of miniature activity and light sensors that can be attached to a collar or jacket and monitored remotely

PSYC388 BIOLOGICAL RHYTHMS AND SLEEP (5 decks)

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