9. biorhythms- circadian

what are biological rhythms?

cyclical changes in the way biological systems (humans, animals, plants) behave.

3 types of biological rhythms

• circadian rhythms

• infradian rhythms

• ultradian rhythms

how long do circadian rhythms last and example?

cycles that generally occur once every 24hrs (e.g. sleep-wake cycle)

how long do infradian rhythms last?

cycles that last longer than 24hr and can be weekly, monthly or annualy (e.g. menstrual cycle)

how long do ultradian rhythms last?

last less than 24hrs (e.g. patterns of sleep)

what regulates the timing of biological rhythms?

factors both inside (endogenous pacemakers) and outside (exogenous zeitgebers) the body

what is the sleep-wake cycle?

24hr rhythmic cycle where there are differing levels of consiciousness. People sleep for a certain time every 24hrs and conduct other activities during wakefulness

how is the circadian rhythm regulated?

1. light (exogenous zeitgeber)

2. detected by eyes

3. travels along optic nerve

4. suprachiasmatic nucleus (SCN), endogenous pacemaker, located in the hypothalamus

5. pineal gland inhibits melatonin

6. feel awake

7. sunset- lack of light (exogenous zeitgeber)

8. detected by eyes

9. travels along optic nerve

10. SCN in hypothalamus

11. pineal gland releases melatonin

12. feel sleepy

what did Siffre do in his cave sudy into circadian rhythms and why?

Siffre went into a cave for 2 months and was completely isolated (no exogenous zeitgebers)

He wanted to study the effects on his circadian rhythm from no natural light, clocks, calendar, sound

He slept and ate only when his body told him to- the only influence was internal body clock (endogenous pacemakers)

what did Siffre find?

his circadian rhythm lengthened slightly to around 25hrs. His lack of external cues made him feel like a day was longer than it actually was. He came out in mid-september but thought it was mid-august

what can we conclude from Siffre’s findings?

• exogenous zeitgebers are necessary to entrain endogenous pacemakers

• suprachiasmatic nucleus will do its job without light

• light is needed to keep both zeitgebers and exogenous pacemakers interacting together

what did Aschoff and Weaver do in their study?

• participants spent 4 weeks in a WW2 bunker

• they had no natural light but could turn artificial light on or off

what did Aschoff and Weaver find?

circadian rhythm of 25hrs, with one p’s extending to 29hrs

Both studies showed cycles settling at just over 24hrs suggesting we use natural light to entrain our pacemakers, associated with the 24hr clock

AO3- small sample sizes and generalisation

p- the research may lack generalisability

e- tends to involve small group of ps, in the case of Siffre, one individual, the people involved may not be representative

e- limits the degree to which meaningful generalisations can be made and applied to the wider population

AO3- confounding variables

p- confounding variables may have skewed results

e- although the ps in Aschoff and Wever’s study had no access to natural light, they still had access to artificial light. Siffre would turn on a light when he woke up which would stay on until he went to bed. They assumed that artificial light what have no effect on free-running circadian rhythm.

e- HOWEVER Cziesler’s research suggested that artificial light can have an influence

l- use of artificial light could have been a confouding variable and affected the validity of the result

AO3- individual differences

p- individual differences may decrease generalisability

e- individual cycles can vary, some people have a natural preference for going to bed early and getting up early, whereas others prefer the opposite

e- There are also age differences in sleep wake patterns

l- individuals seem to have innate differences in their cycle length and onset- these individual differences can further complicate generalisation

AO3- practical applications to shift work

p- research into circadian rhythms has useful applications

e- research has provided a better understanding of the consequences of disrupted circadian rhythms (i.e. shift work).night workers can experience reduced concentration around 6am, making mistakes and accidents more likely

e- actions: longer rests after shifts (suggested at least 24hrs and longer if have worked consecutive nights), longer rotation period (it takes about 7 days to adjust to changes in sleep-wake cycle)

L- highlights economic implications and how changes in shift work patterns could help workers stay healthy and manage productivity