Biological Rhythms

what is a rhythm?

something that is repeated regularly

what is a bio-rhythm and who has it?

• all living organisms have some kind of bio-rhythm

• something that is repeated over different intervals (daily, monthly...)

what are the two things that bio-rhythms are governed by?

endogenous pacemakers and exogenous zeitgebers

what is an endogenous pacemaker?

our internal body clock (suprachiasmatic nucleus)

what is an exogenous zeitgeber?

external clock (e.g. sunlight)

what are the four types of bio-rhythms?

• ultradian

• circadian

• infradian

• circannual

what is an ultradian rhythm?

• occur more than once a day

• occur most in mammals

• an example is sleep as it is divided into several stages

what is a circadian rhythm?

• occurs daily (every 24 hours)

• sleep/wake cycle or body temperature cycle are examples

what is an infradian rhythm?

• occurs less than daily but more often than yearly (e.g. monthly)

• example is the menstrual cycle

• control mechanisms of the menstrual cycle range from influence of pheromones and influence of day/night cycle

what bio-rhythm is the sleep/wake cycle?

a circadian rhythm

what are the two theories to why the sleep/wake cycle is 24 hours long?

1. controlled by an endogenous pacemaker: maintains an internal 24-hour repeating cycle

2. synchronised by an exogenous zeitgeber: such as day/night cycle - each dawn is roughly 24 hours after the last

what does siffre's study show?

• proves internal control he fell asleep without external influence

• show that we need external synchronisation because his day extended to 25 hours (because he fell asleep) - proves endogenous pacemakers control us

what is a summary of siffre's study?

• in 1972 siffre spent 6 months in a texas cave

• no light entered the cave

• he attached electrodes to his head when he slept (measuring sleep cycles)

• his days extended so that his cycle 151 was actually the 179th day

what is an evaluation of siffre's study?

• only one male in the experiment (should be repeated with men and women of all ages)

• the time of year may affect data collected

• it is a case study so specific to siffre

what is wever's study? (supports siffre's argument)

• a group of participants spent 4 weeks in a WW2 bunker without natural light

• all but one of the participants displayed a circadian rhythm between 24-25 hours (the one displayed 29 hours)

• siffre said it is natural if sleep/wake cycles are longer than 24 hours but it is entrained by exogenous zeitgebers associated with out 24 hour day

evaluation of sleep/wake cycle theory: practical application to shift work (strength)

• provides understanding of consequences that occur when they're disrupted

• night workers who do night shifts experience reduced concentration around 6 am meaning mistakes are more likely to happen

• shift work links with poor health

evaluation of sleep/wake cycle theory: practical application to shift work (counterpoint)

• studies investigating shift work often use correlation methods (harder to establish whether desynchronisation of the sleep/wake cycle is a cause of the negative effects

• could be other factors: solomon discovered that high divorce rates in shift workers are due to sleep deprivation and the loss of family time

evaluation of sleep/wake cycle theory: medical treatment (strength)

• circadian rhythms coordinate a number of bodily processes

• chromotheraputics are common (how medical treatment can be administered in a way that corresponds with someone's biological rhythms (people take aspirin at night for heart attacks as they occur most in the morning)

evaluation of sleep/wake cycle theory: individual differences (limitation)

• difficult to generalise (circadian rhythms)

• research is based on a small sample of people (sleep/wake cycles vary)

• charles czeisler found individual differences between sleep/wake cycles varying from 13 to 65 hours

• jeanne duffy found that some have a natural preference for going to bed early/late

evaluation of sleep/wake cycle theory: teenage circadian rhythms (wolfson and carskadon)

• they said schools should start late to fit teenagers chronotype

• hormonal shufts in teenage body mean sleeping is harder and they tend to be sleepy at the start of the day

• research shows late starts benefit academic and behavioural performance

• however, its disruptive for teachers, parents and after school activities

• critics don't believe it reduces sleep deprivation