Biological rhythms: Circadian rhythms Flashcards
CAU Feb 3 (no 16)
Biological rhythms governed by 2 things.
Biological rhythms are periodic activity, governed by:
____________
____________
Some of these rhythms occur many times a day (ultradian rhythms).
Others take more than a day to complete (infradian rhythms).
AO1: Circadian rhythms (~1 cycle/24 hours)
- Internal biological ‘clocks’ (endogenous pacemakers)
- External changes in the environment (exogenous zeitgebers)
The circadian rhythm lasts for about 24 hours.
Circa meaning ____ and diem meaning ____.
What are there are several of?
AO1: Circadian rhythms (~1 cycle/24 hours)
‘about’
‘day’
There are several important types of circadian rhythms, e.g. sleep/wake cycle.
Sleep/wake cycle governed by internal and external mechanisms.
Exogenous zeitgebers; how is the effect of daylight shown?
AO1: Circadian rhythms (~1 cycle/24 hours)
We feel drowsy when it’s night-time and alert during the day.
Sleep/wake cycle governed by internal and external mechanisms.
Endogenous pacemakers; what is meant by the term ‘free-running’?
AO1: Circadian rhythms (~1 cycle/24 hours)
A biological clock left to its own devices’ without the influence of external stimuli (e.g. light).
Sleep/wake cycle governed by internal and external mechanisms.
The basic rhythm is governed by the ____. It lies just above the ____ which provides information from the eyes about light.
What can reset what governs the basic rhythm?
AO1: Circadian rhythms (~1 cycle/24 hours)
‘suprachiasmatic nucleus (SCN)’
‘optic chiasm’
Exogenous zeitgebers (light) can reset the SCN.
Siffre demonstrated a free-running circadian rhythm of about 25 hours.
Siffre spent long periods in dark caves to ____;
* ____
* ____
AO1: Circadian rhythms (~1 cycle/24 hours)
‘examine the effects of free-running biological rhythms’
- 2 months in the Southern Alps (1962) and
- 6 months in Texan caves (1970s).
Siffre demonstrated a free-running circadian rhythm of about 25 hours.
What did Siffre find in each case study?
Importantly?
AO1: Circadian rhythms (~1 cycle/24 hours)
In each case study, Siffre’s free-running circadian rhythm settled down to about 25 hours.
Importantly, he did have a regular sleep/wake cycle.
Aschoff and Wever also found a similar circadian rhythm.
Aschoff and Wever (1976) had a group of participants spend four weeks in a World War 2 bunker deprived of natural light.
What did they find?
AO1: Circadian rhythms (~1 cycle/24 hours)
All but one (whose sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25 hours.
Aschoff and Wever also found a similar circadian rhythm.
What does Siffre’s experience and the bunker study suggest?
AO1: Circadian rhythms (~1 cycle/24 hours)
That the ‘natural’ sleep/wake cycle may be slightly longer than 24 hours but is entrained by exogenous zeitgebers associated with our 24-hour day (eg. daylight hours, mealtimes, etc.).
Endogenous pacemakers are stronger than exogenous zeitbegers.
Folkard et al. (1985) studied a group of 12 people who lived in a dark cave for three weeks, going to bed when the clock said 11.45pm and waking when it said 7.45am.
What did the researchers do?
AO1: Circadian rhythms (~1 cycle/24 hours)
The researchers gradually speeded up the clock (unbeknown to the participants) to a 22-hour day.
Endogenous pacemakers are stronger than exogenous zeitbegers.
What did Folkard et al. find in their study?
AO1: Circadian rhythms (~1 cycle/24 hours)
Only one participant comfortably adjusted to the new regime. This suggests the existence of a strong free-running circadian rhythm not controlled by exogenous zeitgebers.
One strength of circadian rhythm research is application to shift work.
Shift work creates desynchronisation of biological rhythms.
What did Boivin et al. find?
AO3
Boivin et al. (1996) found shift workers experience a lapse of concentration around 6am (a circadian trough) so accidents are more likely.
One strength of circadian rhythm research is application to shift work.
Research also suggests a link between shift work and poor health.
What did Knutsson find in shift workers?
Thus?
Shift workers 3 times more likely to develop heart disease (Knutsson 2003).
Thus, research into the sleep/wake cycle may have economic implications in terms of how best to manage shift work.
Counterpoint to CR research in its application to shift work.
The research is correlational, therefore desynchronisation may not be the cause of observed difficulties.
For example, Solomon (1993) concluded that ____
Suggesting?
AO3
‘high divorce rates in shift workers might be due to missing out on important family events’.
This suggests that it may not be biological factors that create the adverse consequences associated with shiftwork.
Another strength is real-world application to medical treatment.
Circadian rhythms co-ordinate the body’s basic processes (e.g. heart rate, hormone levels) with implications for chronotherapeutics (timing medication to maximise effects on the body).
How and when is aspirin effective?
AO3
Aspirin reduces heart attacks, which are most likely in the morning. Bonten et al. (2015) found taking aspirin is most effective last thing at night.
This shows that circadian rhythm research can help increase the effectiveness of drug treatments.
One limitation is that generalisations are difficult to make.
Studies of the sleep/wake cycle often use small groups of participants (e.g. Aschoff and Wever), or even single individuals (e.g. Siffre).
Participants may ____
Siffre observed that his internal clock ticked more slowly at 60 than when he was younger.
AO3
‘not be representative of the wider population and this limits making meaningful generalisations’.
This suggests that, even when the same person is involved, there are factors that may prevent general conclusions being drawn.
Evaluation extra: Shifting the school day.
Research shows benefits for teenagers’ academics and behavioural performace when lessons start later in the day (Adolescent Sleep Working Group 2014).
However?
AO3
However, a later start is disruptive for parents and teachers, and teenagers may simply stay up later and still be exhausted.
This suggests changing the school day may not be practical even though it may be desirable.
