Circadian Rhythms (bio)

Question 1

What is a biological rhythm?

Answer 1

A change in body processes or behaviour in response to cyclical
changes within the environment e.g. the sleep/wake cycle

Question 2

What causes biological rhythms?

Answer 2

All biological rhythms are governed by two things:
1. The body’s internal biological ‘clocks’, which are called endogenous pacemakers
2. External changes in the environment known as exogenous zeitgebers.

Question 3

What are endogenous pace makers

Answer 3

● Some aspects of our biological rhythms may be genetically determined, eg dopamine levels may affect mood/sleep
● The suprachiasmatic nucleus (SCN) which is part of the hypothalamus may be an internal clock.
● The suprachiasmatic nucleus (SCN) contains neurons that exhibit a circadian pattern of activity and regulate melatonin secretion by the pineal gland in response to the environmental light/dark.

Question 4

What are Exogenous Zietgebers (external influences on the body)

Answer 4

● Light – specifically sunlight is the most influential Zietgeber, triggering the SCN
● Social cues – usually imposed by parents, norms etc.

Question 5

What did Siffre do and find

Answer 5

● Michael Siffre (pronounce ‘Seef’) spent several extended periods underground to study the effects on his own biological rhythms.
● Deprived of exposure to natural light and sound, but with access to adequate food and drink, Siffre re-surfaced in September after two months in the caves of the Southern Alps believing it to be mid-August!
● A decade later, he performed a similar feat but this time for six months in a Texan cave.
● In each case, his ‘free-running’ biological rhythm settled down to one that was just beyond the usual 24 hours (around 25 hours) though he did continue to fall asleep and wake up on a regular schedule.

Question 6

Shift work

Answer 6

● 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).
● Night workers engaged in shift work experience a period of reduced concentration
around 6 in the morning (a circadian trough) meaning mistakes and accidents are
more likely (Boivin et al. 1996).
● Research has also suggested a relationship between shift work and poor health: shift
workers are three times 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, or 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.

Question 7

Jet lag

Answer 7

● Travelling across different time zones can mean that people have to adjust their body clock.
● It can take about a week to adjust to a new time zone
● Less jet lag when travelling East to West, probably because that adds hours to our day.

Question 8

A03 - Case study

Answer 8

1. Studies of the sleep/wake cycle tend to involve small groups of participants, or single individuals, as in the case of Siffre.
2. 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, Siffre observed, at the age of 60, that his internal clock ticked much more slowly than when he was a young man.
3. This illustrates the fact that, even when the same person is involved, there are factors that
   vary which may prevent general conclusions being drawn.
4. This means that the findings of such studies are limited in their generalisations to the wider
   population.

Question 9

A03 - Individual differences

Answer 9

Whilst the sleep/wake cycle is an established theory, it is important to consider the
differences between individuals when it comes to circadian cycles.
2. Duffy et al. (2001) found that ‘morning people’ prefer to rise and go to bed early (about 6
am and 10 pm) whereas ‘evening people’ prefer to wake and go to bed later (about 10 am
and 1 am).
3. This demonstrates that there may be innate individual differences in circadian rhythms,
which suggests that researchers should focus on these differences during investigations.

Question 10

Circadian rhytm

Answer 10

Biological rhythms which last for around 24 hours, e.g. the

sleep/wake cycle and core body temperature