endogenous and exogenous Flashcards
(23 cards)
what are the 2 biological rhythms called
endogenous pacemakers
exogenous zeitgebers
whats an EP
internal mechanisms which determine the biological rhythms of the body e.g. the circadian sleep wake cycle
act as internal ‘body clocks’
what can effect them
the external environment
changes in light levels as light is required to reset the sleep-wake cycle every 24 hours (Siffre’s research supports this, although he found a natural 25-hour cycle)
what is mainly made up on EPs
the supercharismatic nucleus
where is that located
the hypothalamus
what does it send signals to
the pineal gland
what does this increase the production of
increases production of melatonin secretion at night, helping to induce sleep
who did research into EPs
Morgan 1995
what was the procedure
bred hamsters so that their circadian rhythms were 20 hours, rather than the usual 24-hour cycle
SCN neurons from the 20-hour hamsters were transplanted into the brains of normal hamsters.
what does this research represent
concluded that the SCN is a significant endogenous pacemaker which is crucial to the proper functioning of circadian rhythms
1 strength of this
Skene & Arendt (2007): They pointed out that most blind people who still have some light perception have normal circadian rhythms of 24 hours, whereas blind people with no light perception display irregular circadian rhythms
what are 2 weaknesses
Morgan’s study was on hamsters. Humans are very different biologically, cognitively and socially from hamsters. This means that research using hamsters is not generalizable to humans.
Biologically reductionist- may be many other things contributing to the sleep wake cycle being disruptive like high stress level
what are EZs
any factors in the sleep-wake cycle which act as external cues to either wakefulness or sleepiness
whats an example of this
going to bed with the light on or a digital device placed next to the bed may keep levels of light unnaturally high and thus impact negatively on sleep
whats it responsible for
resetting the biological clock
whats the most EZ
light
what are some examples of social cues
the timing of meals (e.g. ‘We eat dinner at 7pm every evening’)
work schedules (e.g. ‘I get to work at 8.30am and leave at 4.30pm)
what occurs between EPs and EZs
synchrony
interact and work alongside each other to set circadian rhythms
who did research on this
Campbell & Murphy (1998)
what was the procedure
15 sleeping participants were woken at various intervals throughout the night
A light pad was shone onto the back of their knees
This resulted in irregular sleep-wake cycles for the participants (as high as three hours deviation for some of them)
what was concluded
light is a key exogenous zeitgeber - even when it shines on the back of the knee rather than being detected by the eye
universal- Studies of pre-industrial societies (e.g. hunter-gatherer tribes in Tanzania, Namibia, and Bolivia- Yetish et al found
People still follow a 24-hour sleep-wake cycle closely linked to sunlight exposure. Even without artificial light or alarms, people wake up before sunrise and go to bed after sunset, showing consistency across cultures due to natural zeitgebers.
limitations
15 is a very small sample size
may be hard to replicate- have been criticized for lacking replication and potentially poor controls.
It’s hard to fully isolate the effects of light without accidentally exposing participants’ eyes- low internal validity.
