Endogenous Pacemakers and Exogenous Zeitgebers Flashcards
What is the Suprachiasmatic Nucleus?
The SCN is a tiny bundle of nerve cells located in the hypothalamus. It is one of the primary endogenous pacemakers and controls the circadian rhythms such as the sleep/wake cycle. Nerve fibres connected to the eye cross in an area called the optic chiasm on their way to the visual area, just below the SCN. It continues during sleep
What was DeCoursey’s study?
She destroyed the SCN connections in the brains of 30 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 were killed by predators.
What is the influence of the pineal gland and melatonin?
The SCN passes information onto the pineal gland to release melatonin during the night. This induces sleep, and is inhibited during periods of wakefulness. Melatonin has also been suggested asa causal factor in SAD.
How is light an exogenous zeitgeber?
IT can reset the SCN, and plays a key role in the maintenance of the sleep-wake cycle. Campbell and Murphy demonstrated that light may be detected by skin receptor sites even with information not received by the eyes. 15 participants were woken at various times and had a light pad shone on the back of their knees. The managed to produce a deviation of S/W cycle of up to 3 hours.
How are social cues an exogenous zeitgeber?
At about 6 weeks the circadian rhythms begin and by 16 weeks they are entrained. The schedule imposed by parents is a key influence here, such as mealtimes, nap times and bedtimes. Research also suggests adapting to local times for eating and sleeping is an effective way of entraining circadian rhythms and beating jet lag when flying long distances.
What is the limitation - beyond the master clock?
Research has revealed there are numerous circadian rhythms in many organs and cels. These are called peripheral oscillators, and act independently of the SCN. This suggests there may be other complex influences on the S/W cycle aside from the master clock.
What is the limitation - ethics in animal studies?
In the DeCoursey study, she must have known she was committing them to certain death in the wild and so whether or not the information we gain from the studies justifies the aversive procedures is a matter of debate.
What is the limitation - influence of exogenous zeitgebers may be overstated?
Miles recounts the story of a young man, blind from birth, with a 25 hour S/W cycle. Despite exposure to social cues, he could not be adjusted and had to take melatonin at night and stimulants in the morning to keep pace with the 24-hr world.
