14.4 - Circadian Sleep Cycles Flashcards Preview

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Flashcards in 14.4 - Circadian Sleep Cycles Deck (42)
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1
Q

Is the sleep-wake cycle the only example of a circadian rhythm?

A

No, most physiological, biochemical and behavioural process is at least a little circadian

2
Q

what is the primary thing that our bodies are adjusting to in terms of our circadian rhythm?

A

the light and dark cycle

3
Q

what do we call environmental factors that influence circadian rhythms?

A

Zeitgebers, which entrain or control the timing go circadian rhythms

4
Q

can we alter circadian cycles by manipulating zeitgebers?

A

yes, in lab settings we can change circadian cycles to a 23 hour day by alternating 11.5 periods of dark and light

5
Q

Do we develop circadian cycles in the absence of the light-dark cycle?

A

Yes, we can, for instance hamsters living in perpetual darkness or light can be entrained by daily bouts of social interaction, boarding, eating or exercise.

6
Q

why do we use hamsters to study circadian rhythms so often?

A

bc their rhythms are extreme.y clear

7
Q

What happens to circadian rhythms in the complete absence of any zeitgebers?
- what do we call these?

A

humans and other animals maintain all their circadian rhythms, which are called free running rhythms in this context, their durationg being termed a free running period

8
Q

what are the primary features of free running periods? (4)

A
  1. vary in length between indiviauls
  2. stable within individuals
  3. usually longer than 24 hours (around 24.2)
  4. extremely regular
9
Q

what did the study of free running rhythms cause us to suspect

A

that there is some internal biological clock that habitually runs a little slow unless entrained by time related cues in the environemtn

10
Q

what does the regularity of free running sleep wake cycles suggest?

A

that circadian rights are the primary regulators of sleep, not recuperation or cognitive/physiological expenditure

11
Q

Are free running circadian cycles learned?

A

No, even rats born and raised in unchanging lab environments display regular free running sleep wake cycles that are slightly longer than 24 hrs

12
Q

Describe internal desynchronization

A
  1. some species display body temp circadian rythhims (temp falls and night and rises in the morning)
  2. if housed in constant lab environments, sleep wake and body temp cycles can break away from one another
13
Q

give a human example of internal desynchronization

A

human volunteer with initial free running sleep wake and body temp rhythms of 25.7 hours

  • increase of sleep wake to 33.4 Horus
  • decrease in BT to 25.1 hours
14
Q

what does intneral desynchronization suggest? (2)

A
  1. there may be more than one circadian thing mechanism,

2. sleep is not causally related to the decreases in body temp normally associated with it

15
Q

what do instances of free running volunteers staying awake longer show us?

A

that recuperation theories cannot be true, bc they still tend to wake at the same time, getting less sleep but remaining consistent
(more wakefulness per cycle, less time for sleep)

16
Q

what are the two disruptors of circadian rhythmicity in modern societies?

A
  1. jet lag

2. shift work

17
Q

explain jet lag in terms of zeitgebers

A
  • zeitgebers controlling phases of various circadian rhythms are accelerated during east bound flights (phase advances)
  • decelerated during west bound flights (phase delays)
18
Q

explain shift work in terms of zeitgebers

A

they remain the same, but workers must adjust her sleep wake cycles in order to meet the demands of the work schedule

19
Q

what do both jet lag and shift work produce in terms of symptoms

A
  1. sleep disturbances
  2. fatigue
  3. genreal malaise
  4. physical ad cognitive dysfunction
20
Q

How long do the effects of phase advances tend to take?

A

upwards of 10 days to adjust to 10 hour phase advances

21
Q

What two behavioural approaches have been proposed to reduce the effects of jet lag?

A
  1. gradually shifting the sleep-wake cycle in the days prior to the flight
  2. administering treatments after the flight that promote the shift in circadian rhythm, for instance melatonin
22
Q

what have companies implying shift workers done to improve productivity?

A
  1. schedule phase delays rather than advances as much as possible (easier to stay awake longer and get up later than it is to go to bed earlier and get up earlier)
23
Q

what is the circadian clock?

A

the bodies’ internal timing mechanism

24
Q

what was the first large breakthrough in the search for the neural basis of the circadian clock?

A

The discovery that large medial hypothalamic lesions disrupt circadian cycles of eating, drinking and activity in rats

25
Q

Specific lesions to what area of the medial hypothalamus were shown to disrupt various circadian cycles, including sleep wake cycles?

A

the suprachiasmatic nuclei of the medial hyp thal

26
Q

what exactly do suphrachiasmatic nuclei lesions induce?

A

abolish the circadian periodicity of sleep cycles, not the amount of time animals sleep

27
Q

what is the non-experimental support for the role of the suprachiasmatic nuclei in circadian rhythms?

A

Nuclei display circadian cycles of electrical, metabolic, and biochemical activity that can be entrained by the light-dark cycle

28
Q

Explain the Ralph and colleagues 1990 study on the SCN and its implications

A
  1. removed the SCN from the fetuses of a strain of mutant hamsters with short free running sleep wake cycles
  2. implanted these SCN into normal adult hamsters whose typical free running sleep wake cycle was abolished by SCN lesions
  3. Transplanted SCN restored the free running sleep wale cycles of the recipients to the 20 hour (short) cycle of the mutant hamsters.
    - transplant in the other direction and the opposite effect
    - Proves conclusively that the SCN is the locus of most circadian rythms
29
Q

what three lines of evidence indicate that the SCN is not the only circadian clock in mammals?

A
  1. bilateral SCN lesions have been shown to leave some circadian rhythms in tact what abolishing others
  2. bilateral SCN lesions dont eliminate the ability of all environmental stimuli to entrain circadian rhythms
  3. similar to SCN neurons, cells from other body parts often display free running circadian cycles of activity when maintained in tissue culture
30
Q

what is an example of the fact that bilateral SCN lesions dont eliminate the ability of all environmental stimuli to entrain circadian rhythms

A

SCN lesions do block entrainment by light, but not by regular food or water availability

31
Q

How do the SCN control circadian rhythms?

A

The timing mechanisms of the SCN depend on the firing patterns of SCN neurons, which tend to inactive at night, begin to fire at dawn, and fire at a slow and steady pace all day.

32
Q

What was the first place that researchers looked to study how light-dark cycles entrained sleep-wake cycles?

A

The eye, trying to identify and track the specific neurons that left the eyes and carried the info about light and dark tha entrained the biological clock

33
Q

what effect did cutting the optic nerve before it reached the optic chiasm have on light entrainment?

A

eliminated its ability to entrain circadian rhythms

34
Q

what effect did cutting the optic tracts after they left the optic chasm have on light entrainment

A

no effect

35
Q

what do the findings surrounding the location of optic nerve lesions and their influence on light entrainment imply?

A

that visual axons critical for the entrainment of circadian rhythms branch off from the optic nerve in the vicinity of the optic chiasm

36
Q

what did the finding that visual axons critical for the entrainment of circadian rhythms branch off from the optic nerve in the vicinity of the optic chiasm lead to?

A

the discovery of the retinohypthalamic tracts, which leave the optic chimes and project to the SCN

37
Q

what is surprising about the influence of light dark cyc/les on the retinohypothalmic tracts and circadian rhythms

A

rods and cones are uneccesary - rather, photoreceptors have been found on retinal ganglion neurons that have unique functional properties

38
Q

what are the unique functional properties of retinal ganglion cells? explain their evolutionary history

A

evolution cased these photoreceptors to loose the ability to respond quickly and briefly to rapid changes in light in favour of the ability to response consistently to slowly changing levels of background illumination

39
Q

what is the photopigment of retinal ganglion photoreceptors?

A

melanopsin

40
Q

what was the important breakthrough that led to the study of the genetics of circadian rythms?

A

some hamsters had abnormally short 20 hour free running circadian rhythms p experiments showed the abnormality was a result of a genetic mutation and the mutated gene was named tau

41
Q

what was the first circadian gene tohave its molecular structure characterized?

A

‘clock’ which was discovered in mice

42
Q

what three discoveries followed from the discovery of circadian genes?

A
  1. same or similar circ. genes have been found in many species of different evolutionary ages, so these genes must have evolved early in evolutionary history and been conserved.
  2. key mechanism of circ. genes is gene expression, or the transcription of proteins by the circadian genes displays a circadian cycle
  3. proved to be a more direct method of exploring the circadian timing capacities of parts of the body other than the SCN - molecular circadian timing mechanisms similar to these in the SCN exist in most cells ot the body. Most cellular clocks are regulated by neural and hormonal signals from the SCN.