the effect of endogenous pacemakers and exogeneous zeitbergs on the sleep wake cycle Flashcards
endogenous pacemakers
internal body clocks that regulate our biological rhythms eg suprachiasmatic nucleus on the sleep wake cycle
exogenous zeitbergs
external factors in the environment such as light that reset our biological clocks through entrainment
sleep/wake cycle
daily cycle of biological activity based on 24 hours period thats influenced by regular variations in the environment such as alteration in night and day
what is the suprachiasmatic nucleus
a bundle of nerve cells located in the hypothalamus in the brain
what is the suprachiasmatic nucleus used for
maintaining sleep wake cycle by processing information about light
- as nerve fibres are connected to eyes
how is the biological clock kept in time with changing patterns of daylight
light can penetrate through eyelids allowing biological clock to adjust
what are the 2 studies demonstrating influence on SCN on sleep wake cycle
- decoursey
- morgan
outline decourseys study
DeCoursey et al destroyed the SCN connections in the brains of 30 chipmunks.
* The chipmunks were then returned to their natural environment and observed for 80 days.
* The observations taken showed that the sleep-wake cycle of the chipmunks had disappeared.
* In addition, by the end of the study a significant proportion of the chipmunks had been killed by
predators – probably because they were awake and vulnerable when they should have been
asleep.
outline morgans study
Morgan et al bred a strain of hamsters so that they had abnormal circadian rhythms of 20 hours
instead of 24 hours.
* SCN neurons from these abnormal hamsters were then transplanted into the brains of normal
hamsters.
* These normal hamsters then displayed the same abnormal circadian rhythm of 20 hours, showing
that the transplanted SCN had imposed its pattern onto the recipients’ brains.
* Furthermore, in a reverse experiment, when implanting SCN neurons from a normal hamster into
the brain of an abnormal hamster, the recipient hamster’s circadian rhythm changed to 24 hours.
issues of extrapolation with the studies
As always with animal studies, there are issues associated with the extrapolation of findings to
humans.
E For example, in the case of Morgan’s research, it is not certain that transplanting SCN neurons into
human brains would have the same affect since human brains are far more sophisticated than those
of hamsters.
E This means that any conclusions drawn from this research in relation to the significance of
endogenous pacemakers in maintaining circadian rhythms must be treated with caution.
E+ However, although hamsters are less sophisticated than humans, they are neverthless sufficiently
similar to argue that it is likely that the SCN also plays a significant role in maintaining the circadian
rhythms of humans.
pineal gland
endogenous pacemaker in brain
what does pineal gland do
receives information about day length and light from SCN
and secretes melatonin in accordance to this
- secreted at night, inhibited during the day
endogenous pacemakers are hard to study
Endogenous pacemakers are essentially impossible to study in isolation from other factors which
may affect the sleep/wake cycle such as light or social cues.
E Even Siffre used artificial light in his cave study – which may have reset his biological clock.
E This means it is very difficult to prove the significance of the role played by endogenous pacemakers
in the sleep/wake cycle particularly since, in ‘real life’, endogenous pacemakers and exogenous
zeitgebers interact.
what are the 2 exogenous zeitbergs
- light
- social cues
what does light influence
the sleep wake cycle and can reset the SCN
how do social cues affect the sleep wake cycle
the sleep wake cycle of new born babies is essential random
- at 6 weeks circadian rhythms begin and by 16 weeks they have been entrained by schedules imposed by their parents
entrainment
an individuals physical and mental adaptation to the time zone they live in
inconsistent environmental effect
Exogenous zeitgebers do not have the same effect in all environments.
E For example, the Inuits of the Arctic Circle, who spend six months of the year in near total darkness,
nevertheless have the same sleep/wake cycle all year long.
E This suggests that endogenous pacemakers are far more important in regulating the sleep/wake
cycle than exogenous zeitgebers such as light.
case study evidence against
A number of case studies suggest that the effect of exogenous zeitgebers on the sleep-wake cycle
has been exaggerated.
E For example, a case study conducted by Miles et. al. (1977) found that a young man blind from birth
had an abnormal circadian rhythm of 24.9 hours despite exposure to social cues such as regular
mealtimes.
E This suggests that social cues alone are insufficient to determine the sleep/wake cycle and that
other factors must, therefore, be involved.
