biopsychology: endogenous pacemakers and exogenous zeitgebers Flashcards
(19 cards)
What are endogenous pacemakers?
Internal body clocks that regulate biological rhythms
* eg: influence of SCN on the sleep-wake cycle
What role does the SCN play in the body?
It generates the body’s circadian rhythm and acts as a master clock > it has links to other brain regions that control sleep and arousal
What are exogenous zeitgebers?
External cues that affect or entrain biological rhythms
* eg: light influencing the sleep/wake cycle
Where is the SCN located?
In the hypothalamus in each hemisphere of the brain > it is a tiny bundle of nerve cells
How does the SCN respond to light?
It sends signals throughout the body in response to light and dark
It also needs resetting when external light levels change
What information does the SCN receive?
Information about light levels via the optic nerve > This occurs even when eyes are closed because light penetrates the eyelids
What hormone does the SCN regulate?
the manufacture and secretion melatonin in the pineal gland > the SCN directs the release from the pineal gland at night
What is the function of melatonin?
Induces sleep by inhibiting brain mechanisms that promote wakefulness
melatonin levels increase at night and decrease as light levels rise
What is the relationship between the pineal gland and the SCN?
They function jointly as endogenous pacemakers in the brain
Fill in the blank: The SCN sends signals to the pineal gland to _______ melatonin at night.
[increase]
Fill in the blank: The SCN sends signals to the pineal gland to _______ melatonin as light levels increase.
[decrease]
state 2 types of exogenous zeitgebers
- light
- social cues
explain how light works as an exogenous zeitgeber
It can reset the body’s main endogenous pacemaker, the SCN and thus plays a role in the maintenance of the sleep-wake cycle.
Light also has an indirect influence on key processes in the body that control such functions as hormone secretion and blood circulation.
explain how social cues work as exogenous zeitgebers
- All infants begin with a random sleep/ wake cycle, it isn’t until about 16 weeks that most babies circadian rhythms become entrained. Entrainment is the interaction between internal and external factors that determine our sleep/ wake cycle. Schedules are usually imposed by adults including adult determined meal times and bedtimes.
- Another social cue is jetlag going to another country where there are different local times for eating and sleeping. We are able to entrain this influence by changing our eating patterns and sleeping patterns to that of the culture (rather than based on hunger and fatigue).
AO3: research to support > animal studies
There is support of the role of SCN from animal studies
DeCoursey et al (2000) destroyed the SCN connections in the brains of chipmunks who were then returned to their natural habitat and observed for 80 days. The sleep wake cycle of the chipmunks disappeared and by the end of the study a significant proportion of them had been killed by predators. This suggests that the SCN plays an important role in the sleep wake cycle, as without an SCN the cycle is non-existent. We can generalise the findings of animal studies of the sleep wake cycle to humans as there are similar mechanisms such as the SCN and pineal gland. So generalisations about the role of the SCN apply to humans.
Counter: However, the study from DeCoursey et al was extremely unethical as the animals were exposed to harm and risk when they returned back to their natural habitat. So the issue is whether the importance of such findings outweighs the aversive procedure.
AO3: SCN may obscure other body clocks
One weakness of SCN research is that it may obscure other body clocks
Research has revealed that there are numerous circadian rhythms in many organs and cells in the body. These peripheral oscillators are found in the organs including the lungs, pancreas and skin. They are influenced by the actions of the SCN, but also act independently. It has been demonstrated how changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours, whilst leaving the rhythm of the SCN unaffected.
WEAKNESS as this suggests that there may be many other complex influences on the sleep-wake cycle, aside from the SCN.
AO3: research to support > exogenous zeitgebers
There is research to support the influence of exogenous zeitgebers on the sleep wake cycle.
Campbell and Murphy (1998) demonstrated that light may be detected by skin receptor sites. 15 participants were woken at different times and light shone on the back of their knees. They managed to produce a deviation in the participants usual sleep/wake cycle of up to 3 hours in some cases.
STRENGTH as this suggests that light is a powerful zeitgeber that need not necessarily rely on the eyes.
AO3: research to go against > exogenous zeitgebers
One limitation is that exogenous zeitgebers do not have the same effect in all environments
For example, people who live within the Artic circle have similar sleep patterns all year round despite spending around six months in almost total darkness
WEAKNESS as this suggests that the sleep-wake cycle is primarily controlled by endogenous pacemakers that can override environmental
changes in light
AO3: exogenous zeitgebers may be overstated
A weakness is that the influence of exogenous zeitgebers may be overstated
Miles studied a young man, blind from birth who had an abnormal circadian rhythm of 24.9 hours. Despite exposure to social cues such as regular meal times, his sleep/wake cycle could not be adjusted.
WEAKNESS as this suggests that social cues, such as regular mealtimes, his sleep wake cycle could not be adjusted. As a result the role of exogenous zeitgebers may be overstated.
COUNTER: can’t generalise findings from a unique case