6.7: Circadian rhythms Flashcards Preview

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Flashcards in 6.7: Circadian rhythms Deck (28)
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1
Q

Biological rhythms

A

Biological rhythms are distinct patterns of changes in body activity that conform to cyclical time periods

2
Q

Biological rhythms are distinct patterns of changes in body activity that conform to cyclical time periods.
What are biological rhythms influenced by?

A

Biological rhythms are influenced by internal body clocks (endogenous pacemakers) as well as external changes in the environment (exogenous zeitgebers)

3
Q

Circadian rhythm

A

A circadian rhythm is a type of biological rhythm, subject to a 24 hour cycle, which regulates a number of body processes such as the sleep/wake cycle and changes in core body temperature

4
Q

All living organisms - plants, animals and humans - are subject to biological rhythms and these exert an important influence on the way in which body systems behave.
All biological rhythms are governed by two things: The body’s internal biological ‘clocks,’ which are called endogenous pacemakers and external changes in the environment known as exogenous zeitgebers.
Some of these rhythms occur many times during the day (what)?

A

Some of these rhythms occur many times during the day (ultradian rhythms)

5
Q

All living organisms - plants, animals and humans - are subject to biological rhythms and these exert an important influence on the way in which body systems behave.
All biological rhythms are governed by two things: The body’s internal biological ‘clocks,’ which are called endogenous pacemakers and external changes in the environment known as exogenous zeitgebers.
Some of these rhythms occur many times during the day (ultradian rhythms).
Others take longer than a day to complete (what)?

A

Others take longer than a day to complete (infradian rhythms)

6
Q

All living organisms - plants, animals and humans - are subject to biological rhythms and these exert an important influence on the way in which body systems behave.
All biological rhythms are governed by two things: The body’s internal biological ‘clocks,’ which are called endogenous pacemakers and external changes in the environment known as exogenous zeitgebers.
Some of these rhythms occur many times during the day (ultradian rhythms).
Others take longer than a day to complete (infradian rhythms) and in some cases much longer (what)?

A

Others take longer than a day to complete (infradian rhythms) and in some cases much longer (circannual rhythms)

7
Q

Circadian rhythms last for around 24 hours.

What does ‘circa’ mean?

A

‘Circa’ means about

8
Q

Circadian rhythms last for around 24 hours.

‘Circa’ means about and what does ‘diem’ mean?

A

‘Circa’ means about and ‘diem’ means day

9
Q

What does the fact that we feel drowsy when it’s night-time and alert during the day demonstrate?

A

The fact that we feel drowsy when it’s night-time and alert during the day demonstrates the effect of daylight, an important exogenous zeitgeber, on our sleep/wake cycle

10
Q

The fact that we feel drowsy when it’s night-time and alert during the day demonstrates the effect of daylight, an important exogenous zeitgeber, on our sleep/wake cycle.
What does free-running mean?

A

Free-running means that the biological clock is left without the influence of external stimuli like light

11
Q

The fact that we feel drowsy when it’s night-time and alert during the day demonstrates the effect of daylight, an important exogenous zeitgeber, on our sleep/wake cycle.
Free-running means that the biological clock is left without the influence of external stimuli like light.
If we had no idea whether it was night or day, would we still fall asleep and wake up at regular times?
What have several studies tried to do?

A

Several studies have tried to answer this question

12
Q

Aschoff and Wever convinced a group of participants to spend four weeks in a WW2 bunker, deprived of natural light.
All but one of the participants (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25 hours.
Both Siffre’s experience and the bunker study suggest that the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours, but that it is entrained by exogenous zeitgebers associated with our 24 hour day (such as the number of daylight hours, typical mealtimes, ect).
Despite this, we should not overestimate the influence of environmental cues on our internal biological clock.

Folkard et al. studied a group of 12 people who agreed to live in a dark cave for 3 weeks, going to bed when the clock said 11:45am and waking up when it said 7:45am.
Over the course of the study, the researchers gradually sped up the clock (unbeknown to the participants), so an apparent 24 hour day eventually lasted only 22 hours.
It was revealed that not one of the participants was able to comfortably adjust to the new regime.
This would suggest the existence of a strong free-running circadian rhythm that cannot easily be overridden by changes in the external environment

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13
Q

Evaluation:
Strengths:
1. Practical application to shift work.
Knowledge of circadian rhythms has given researchers a better understanding of the adverse consequences that can occur as a result of their disruption (known as desynchronisation).
For example, night workers engaged in shift work experience a period of reduced concentration around 6am (a circadian trough), meaning that mistakes and accidents are more likely (Boivin et al.).
Boivin et al. (1996) found that night workers experience a ‘circadian trough’ at about 6am, as artificial light did not fully reset their circadian rhythm.
Czeisler et al.’s ‘shift rotation’ study (1982). Given that phase delay needs less adjustment than phase advance, it is better to rotate with the clock than against it. This means that it is better to progress from early shift to day shift to night shift, rather than the other way around, from night shift to day shift to early shift. The system was also changed from rapid rotation to slow rotation where shifts changed every 21 days. Czeisler et al. tested this in a chemical plant where workers reported feeling better and less tired and managers reported increasing productivity and fewer errors.
Czeisler et al. found that shift workers at a chemical plant reported high levels of stress, difficulty sleeping and health problems that affecting productivity. The workers were on a backward shift rotation (nights, then afternoons, then mornings), which was causing their sleep-wake cycles to phase advance (effectively shortening the 24 hour cycle). Czeisler introduced a forward shift rotation (nights, then mornings, then afternoons) to phase delay the sleep-wake cycle and placed workers on each shift stage for 21 days to allow the body clock time to fully adjust. After 9 months, the workers reported less stress, found it easier to sleep and had increased productivity.
Gordon et al. (1986) changed Philadelphia police officers from a backward shift rotation (phase advanced) to a forward shift rotation (phase delayed), finding that the police officers were more alert and had 40% fewer accidents.
Reinberg (1984) found that those who were happiest had circadian rhythms that changed the least. Those that were unhappy were the ones whose rhythm changed with the shifts.
An effective alternative to rotating shift patterns is permanent non-rotating shift work (always working nights or evenings). Philips et al. (1991) found that when this was introduced for Kentucky police officers, the rate of sleeping at work was lower and they also had fewer accidents. Permanent shifts, however, can lead to other problems, as they cause difficulty with social and family life.
Research has also suggested a relationship between shift work and poor health.
Knutsson (1986) found that people who work shifts for more than 15 years were 3 times more likely to develop cardiovascular disease.
Knutsson found that shift workers are 3x more likely to develop heart disease, which may in part be due to the stress of adjusting to different sleep/wake patterns and the lack of poor quality sleep during the day.
Thus, research into the sleep/wake cycle may have economic implications in terms of how best to manage worker productivity.

  1. Practical application to drug treatments.
    Circadian rhythms coordinate a number of the body’s basic processes such as heart rate, digestion and hormone levels.
    This in turn has an effect on pharmacokinetics, the action of drugs on the body and how well they are absorbed and distributed.
    Research into circadian rhythms has revealed that there are certain peak times during the day or night when drugs are likely to be at their most effective.
    This has led to the development of guidelines to do with the timing of drug dosing for a whole range of medications including anticancer, cardiovascular, respiratory, anti-ulcer and anti-epileptic drugs (Baraldo).

Weaknesses:
1. Use of case studies and small samples.
Studies of the sleep/wake cycle tend to involve small groups of participants, as in the experiment by Ascoff and Wever, or studies of single individuals, as in the case of Siffre.
The people involved may not be representative of the wider population and this limits the extent to which meaningful generalisations can be made.
In his most recent cave experience in 1999, Sifree observed, at the age of 60, that his internal clock ticked much more slowly than when he was a young man.
This illustrates the fact that, even when the same person is involved, there are factors that vary which may prevent general conclusions being drawn.

  1. Poor control in studies.
    Although participants in the studies were deprived of natural light, they still had access to artificial light.
    For example, Siffre turned on a lamp every time he woke up which remained on until he went to bed.
    It was assumed by him and others that artificial light, unlike daylight, would have no effect on the free-running biological rhythm.
    However, in tests, Czeisler et al. (1999) were able to adjust participants’ circadian rhythms from 22 to 28 hours using dim lighting.
    As such, the use of a light may be analogous to participants taking a drug that resets their biological clock.
  2. Individual differences.
    One further issue that complicates the generalisation of findings from studies of the sleep/wake cycle is that individual cycles can vary, in some cases from 13 to 65 hours (Czeisler et al).
    As well as this, a study by Duffy et al. revealed that some people display a natural preference for going to bed early and rising early (larks), whereas some people prefer the opposite (owls).
    There are also age differences in sleep/wake cycle patterns.

Core body temperature varies by around two degrees Celsius during the course of a day.
It is at its lowest around 4am (36 degrees Celsius) and peaks around 6pm at 38 degrees Celsius.
Evidence suggests that body temperature may have an effect on our mental abilities - the warmer we are (internally), the better our cognitive performance.
Folkard et al. demonstrated how children who had stories read to them at 3pm showed superior recall and comprehension after a week compared to children who heart the same stories at 9am.
Similarly, Gupta found improved performance on IQ tests when participants were assessed at 7pm as opposed to 2pm and 9am

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14
Q

Circadian rhythms repeat in a cycle of what?

A

Circadian rhythms repeat in a cycle of once every 24 hours

15
Q

Circadian rhythms repeat in a cycle of once every 24 hours.

How many circadian rhythms do mammals possess?

A

Mammals possess about 100 circadian rhythms

16
Q

Circadian rhythms repeat in a cycle of once every 24 hours.
Mammals possess about 100 circadian rhythms.
The 24 hour sleep/wake cycle is a good example of a circadian rhythm, why?

A

The 24 hour sleep/wake cycle is a good example of a circadian rhythm, because it clearly illustrates that circadian rhythms depend on an interaction of physiological and psychological processes

17
Q

Circadian rhythms repeat in a cycle of once every 24 hours.
Mammals possess about 100 circadian rhythms.
The 24 hour sleep/wake cycle is a good example of a circadian rhythm, because it clearly illustrates that circadian rhythms depend on an interaction of physiological and psychological processes.
What does our fairly consistent sleep pattern suggest?

A

Our fairly consistent sleep pattern suggests an internal or endogenous pacemaker mechanism - the biological clock

18
Q

Circadian rhythms repeat in a cycle of once every 24 hours.
Mammals possess about 100 circadian rhythms.
The 24 hour sleep/wake cycle is a good example of a circadian rhythm, because it clearly illustrates that circadian rhythms depend on an interaction of physiological and psychological processes.
Our fairly consistent sleep pattern suggests an internal or endogenous pacemaker mechanism - the biological clock.
However, what can this be overridden by?

A

However, this can be overridden by psychological factors

19
Q

Circadian rhythms repeat in a cycle of once every 24 hours.
Mammals possess about 100 circadian rhythms.
The 24 hour sleep/wake cycle is a good example of a circadian rhythm, because it clearly illustrates that circadian rhythms depend on an interaction of physiological and psychological processes.
Our fairly consistent sleep pattern suggests an internal or endogenous pacemaker mechanism - the biological clock.
However, this can be overridden by psychological factors, such as what?

A

However, this can be overridden by psychological factors, such as anxiety or light - exogenous zeitgebers

20
Q

What is the sleep/wake cycle usually measured by?

A

The sleep/wake cycle is usually measured by reading the time and regular events like when we eat and go to sleep

21
Q

The sleep/wake cycle is usually measured by reading the time and regular events like when we eat and go to sleep.
What is our body clock regulated by?

A

Our body clock is regulated by an internal system including factors such as the release of hormones like melatonin, metabolic rate and body temperature

22
Q

Monk and Folkard’s ‘types of shift work’ study (1983). Monk and Folkard identified two major types of shift work – Rapid rotation where the worker changes shifts approximately every 3rd shift and slow rotation, where the worker changes shifts every week or month. Changing every week often means that workers move back one shift every time, which has the same effect of flying West to East

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23
Q

One strength of research into circadian rhythms

A

One strength of research into circadian rhythms is that it has real world application and helps our understanding of desynchronisation and its economic implications due to its impact on workers

24
Q

One strength of research into circadian rhythms is that it has real world application and helps our understanding of desynchronisation and its economic implications due to its impact on workers.
Example

A

For example, Boivin (1996) found that shift workers are most likely to have accidents at 6am when concentration levels dip and Knuttson (2003) found that shift workers are more likely to have poor health, such as heart disease, caused by the stress of adjusting to different sleep/wake patterns

25
Q

One strength of research into circadian rhythms is that it has real world application and helps our understanding of desynchronisation and its economic implications due to its impact on workers.
For example, Boivin (1996) found that shift workers are most likely to have accidents at 6am when concentration levels dip and Knuttson (2003) found that shift workers are more likely to have poor health, such as heart disease, caused by the stress of adjusting to different sleep/wake patterns.
In addition,

A

In addition, we have a better understanding of when to take medication for it to have the biggest impact (pharmacokinetics)

26
Q

One strength of research into circadian rhythms is that it has real world application and helps our understanding of desynchronisation and its economic implications due to its impact on workers.
For example, Boivin (1996) found that shift workers are most likely to have accidents at 6am when concentration levels dip and Knuttson (2003) found that shift workers are more likely to have poor health, such as heart disease, caused by the stress of adjusting to different sleep/wake patterns.
In addition, we have a better understanding of when to take medication for it to have the biggest impact (pharmacokinetics).

One limitation of research into circadian rhythms

A

One limitation of research into circadian rhythms is that the research didn’t control for the impact of artificial light

27
Q

One strength of research into circadian rhythms is that it has real world application and helps our understanding of desynchronisation and its economic implications due to its impact on workers.
For example, Boivin (1996) found that shift workers are most likely to have accidents at 6am when concentration levels dip and Knuttson (2003) found that shift workers are more likely to have poor health, such as heart disease, caused by the stress of adjusting to different sleep/wake patterns.
In addition, we have a better understanding of when to take medication for it to have the biggest impact (pharmacokinetics).

One limitation of research into circadian rhythms is that the research didn’t control for the impact of artificial light.
Example

A

For example, Siffre had a head lamp and Czeisler found that rhythms could be shifted by 3 hours using artificial light

28
Q

One strength of research into circadian rhythms is that it has real world application and helps our understanding of desynchronisation and its economic implications due to its impact on workers.
For example, Boivin (1996) found that shift workers are most likely to have accidents at 6am when concentration levels dip and Knuttson (2003) found that shift workers are more likely to have poor health, such as heart disease, caused by the stress of adjusting to different sleep/wake patterns.
In addition, we have a better understanding of when to take medication for it to have the biggest impact (pharmacokinetics).

One limitation of research into circadian rhythms is that the research didn’t control for the impact of artificial light.
For example, Siffre had a head lamp and Czeisler found that rhythms could be shifted by 3 hours using artificial light.
Why does this matter?

A

This matters because we can’t identify the true nature of a free running clock as it has been altered in the experimental conditions

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