Circadian Rhythms Flashcards
Biological Rhythms
All living organisms are subject to biological rhythms - which exert an important influence on the way our body systems behave.
All biological rhythms are governed by 2 thing:
The body’s internal ‘clocks’ (endogenous pacemakers)
External changes in the environment (exogenous zeitgebers)
Some of these rhythms occur many times during the day (ultradian rhythms)
Some take a day to complete (infradian rhythms)
In some cases, much longer (circannual rhythms)
Circadian rhythms are rhythms which last for around 24 hours (circa=about)
2 examples of circadian rhythms are the sleep/ wake cycle and core body temperature
sleep wake cycle
feeling drowsy at night and alert during the day shows the effect of daylight (an important exogenous zeitgeber on our sleep wake cycle)
The sleep /wake cycle is also demonstrated by the internal (endogenous) pacemaker -biological ‘clock’ - suprachiasmatic nucleus - SCN.
The SCN lies just above the optic chiasm which provides information from the eye about light.
Exogenous zeitgebers (light) can reset the SCN.
Siffre’s cave study
- Siffre is a self styled caveman - he spent an extended period of time underground studying the effects of his own biological rhythms
- deprived from natural light and noises
- resurfaced in mid September 1962 after 2 months believing it to be mid august
- he then repeated this again a decade later for 6 months
- in each cases, his free running biological rhythms settled down to one just beyond 24 hours (around 25)
he did continue to fall asleep / wake on a regular schedule
Aschoff and Wever study WW2 bunker
convinced a group of participants to spend 4 weeks in WW2 bunker deprived of natural light
All but one of the participants (whose sleep/wake cycle extended 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, etc
The influence of exogenous zeitgebers on our internal biological clock is powerful.
Strength - shift work
Strength of research into circadian rhythms - it provides an understanding of the adverse consequences when they are disrupted (desynchronisation)
E.g. night workers engaged in shift work experience a period of reduced concentration around 6 in the morning (a circadian trough) - mistakes and accidents are more likely (Boivin)
Research has also pointed to a relationship between shift work and poor health - shift workers are 3 times more likely to develop heart disease than people who work more typical work patterns (Knutsson)
This shows that research into the sleep/wake cycle may have real-world economic implications in terms of how best to manage worker productivity
Folkard study - cave and chnaging times
Folkard studied a group of 12 people who agreed to live in a dark cave for three weeks, retiring to a bed when the clock said 11:45 pm and rising when it said 7:45 am
Over the course of the study, the researchers gradually speeded up the clock (unbeknown to the participants) so an apparent 24-hour day eventually lasted only 22 hours.
Only one of the participants was able to comfortably adjust to the new regime
This suggested the existence of a strong free-running circadian rhythm which can’t be easily overridden by exogenous zeitgebers
Counterpoint to shift work strength
Studies investigating the effects of shift work tend to use correlational methods
This means that its difficult to establish whether desynchronisation of the sleep/wake cycle is actually a cause of negative effects
Solomon concluded that high divorce rates in shift workers might be due to the strain of deprived sleep and other influences such as missing out on important family events.
This suggests that it may not be biological factors that create the adverse consequences associated with shift work
strength - medical treatment
Research into circadian rhythms - used to improve medical treatments
Circadian rhythms coordinate a number of the body’s basic processes such as heart rate, digestion and hormone levels. These rise and fall during the day which has led to the field of chronotherapeutics - how medical treatment can be administered in a way that corresponds to a person’s biological rhythms
E.g. aspirin reduces blood platelet activity and this can reduce the risk of heart attack,
Heart attacks are most likely to occur early in the morning, so the timing of taking aspirin matterns
Research has supported this (Bonten). This shows that circadian rhythm research can help increase the effectiveness of drug treatments.
Limitation - individual differences
Limitation of research into circadian rhythms is that generalisations are difficult to make
Studies (Aschoff, Wever and Siffre) are based on very small samples of participants.
It seems that sleep/wake cycles may vary widely from person to person. Research by Czeisler found individual differences in sleep/ wake cycles varying from 13 to 65 hours.
A study by Duffy revealed that some people have a natural preference for going to bed early and rising early whereas others prefer the opposite.
Siffre, in a later study observed that his own sleep/wake cycle had slowed down since he was a young man
This means that it is difficult to use the research data to discuss anything more than averaged which may be meaningless
