biological rhythms Flashcards
what are biological rhythms governed by
- endogenous pacemakers
- exogenous zeitbergs
what are the three types of biological rhythms
- circadian rhythms
- infradian rhythms
- ultradian rhythms
circadian rhythms
a biological rhythm that lasts about 24 hours
what are examples of circadian rhythms
the sleep wake cycle
core body temperature
what does the circadian rhythm control
when were sleeping and when we should be awake
what is the sleep wake cycle controlled by
the suprachiasmatic nucleus in the hypothalamus (EP)
- light and darkness (EZ)
when is sleep drive strongest
between 2-4 am and 1-3pm
when is core body temp at its lowest
at 4:30 am
when is core body temp at its highest
at 6pm
why does body temperature rise during last hours of sleep
promoting a feeling of alertness in the morning
when does core body temp drop slightly
between 2pm-4pm
whats the supporting study for circadian rhythms
siffre
aim of siffres study
To investigate the duration of circadian rhythms - in particular the
sleep/wake cycle
method of siffres study
Siffre isolated himself from all daylight by spending 6 months in a dark
cave, with only artificial light to help him navigate within the cave. He had
no clock or any reference to time however he did have verbal contact with the outside world.
what were the results of siffres study
His internal body clock was allowed to ‘free-run’ and at first it was erratic. However, it eventually
settled into a sleep/wake cycle of 25-30 hours. He continued to fall asleep and wake up on a
regular schedule. However, he lost track of how long he had been in the cave, believing it to be
one month less than he had stayed in.
what was the conclusion of siffres study
This suggests that in the absence of exogenous zeitgebers such as natural light sources, circadian
rhythms are roughly maintained which supports the existence of an internal body clock – that the
sleep/has a wake cycle is 24 hours (endogenous pacemaker). However, it also suggests that
exogenous zeitgebers are vital for keeping an individual to a 24-hour cycle (artificial light, contact
with the outside world) and therefore exogenous zeitgebers and endogenous pacemakers work
together.
case study
Siffre’s research – with himself as the sole participant – suffers from the fact that it is by its
very nature potentially unrepresentative/has low population validity.
E Consequently, we cannot be certain that his findings in relation to the fact that exogenous
zeitgebers and endogenous pacemakers work together are valid as they may apply universally.
E However, there is no reason to believe that Siffre is not, in fact, a normal member of the
human race – and hence it is perfectly possible that his findings do indeed apply to others.
artificial light does effect circadian rhythms
A limitation of Siffre’s research is that he did have access to artificial light which he assumed
would not affect his circadian rhythms
E However, Czeizler et.al. managed to alter participant’s circadian rhythms down to 22 hours and
up to 28 hours using dim artificial light alone.
E This is a limitation of Siffre’s findings because it may have been the artificial light maintaining
his sleep-wake cycle and therefore his conclusion that a ‘free-running’ circadian rhythm of
around 24 hours exists may not be valid.
practical application to shift work
A strength of research into circadian rhythms such as Siffre’s is that it has practical applications
for shift work.
E Research has shown that night workers engaging in shift work experience a period of reduced
concentration at around 6 in the morning meaning that mistakes and accidents are more likely.
Furthermore, research has also suggested a relationship between shift work and poor health
e.g. shift workers are three times more likely to develop heart disease (Knutsson, 2003) which
may be in part due to the stress of adjusting to different sleep/wake patterns and the lack of
poor quality sleep during the day.
E This is a strength because research into the sleep/wake cycle may have economic implications
in terms of how best to manage worker productivity and safety.
individual differences in cycle length
The claim that all humans have the same circadian rhythm that is governed by endogenous
pacemakers has been criticised as some research has demonstrated individual differences in
the sleep/wake cycle.
E For example, Czeisler et al (1999) found that sleep-wake cycles varied in some cases from 13 to
65 hours. Duffy et al (2001) found that some people display a natural preference for going to
bed early and rising early and others are the opposite.
E This is a limitation of some research into circadian rhythms because it suggests that not
everyone’s sleep-wake cycles are the same and therefore it is not possible to claim that all
individuals have the same/similar endogenous pacemakers.
