endogenous pacemakers and exogenous Zeitgebers

Question 1

endogenous pacemakers

Answer 1

internal bodily regulators of biological rhythms affecting or entraining biological rhythms to conform to certain cycles

Question 2

suprachiasmatic nucleus SCN

Answer 2

receives info about day light and day length from eyes , processed by visual area in occipital lobe and relayed to SCN via the optic chasm,

Question 3

the SCN after receiving this information , processes it and triggers different rates of release of melatonin from the pineal gland

Answer 3

increased melatonin = decreased serotonin production , creating feelings of sleepiness during the night time where this is little expose to light

Question 4

when their is high exposure to light the SCN triggers the pineal gland to release less melatonin over a long period of time resulting in

Answer 4

increases serotonin production creating feelings of wakefulness

Question 5

the effects of the SCN was demonstrated by
DeCoursey et al 2000
who surgically lesioned the SCNS of 30 chipmunks and compared their natural habitat with 17 controls , the researcher found that

Answer 5

the vast amount of the experimental group had been killed within the first 80 days after being returned to their habitat and episodes of nocturnal movement were detected , especially in the SCN

Question 6

Ralph et al
extracted cells from hamsters which showed abnormal sleep wake cycles and inserted these cells into healthy hamster foetuses
the researchers found that

Answer 6

the restored rhythms always exhibited the period of donor genotype , regardless of the direction of the transplant or genotype of the host.
the basic period of overt circadian rhythm therefore is determined by cells of the suprachriasmatic region

Question 7

exogenous zeitgeebrs

Answer 7

external environment changes , affecting or entraining biological rhythms to conform to certain cyclical time periods

Question 8

social cues are an example of exogenous zeitgeebrs which entrain biological rhythms these include

Answer 8

set meal times
bed time
which signify when to wake up and sleep

Question 9

an example of the effect of exogenous zeitgebers would be to role of light entraining the sleep wake cycle as demonstrated by

Answer 9

siffre et al and Campbell Murphy

Question 10

the influence of the SCN may be overstated
for example Damiola et al demonstrated that the circadian rhythm of mice liver cells could be influenced to experience a 12 hour discerepency leaving the SCN unaffected , these so called

Answer 10

peripheral oscillators also present in the adrenal gland and lungs and collections or systems of cells which act independently of the SCN , each having their own biologival rhythm
therefore the SCN is not as important as once thought

Question 11

there are considerable ethical issues with the use of animals in such research
particularly ion they are deliberately out in harms way as the case with Decoursey et al , thus breaching the BPS ethical guideline or protection from psychological and physical harm . although this does not impact

Answer 11

upon the utility or validity of the findings , a cost benefit analyses would’ve been conducted to assess wether such ethical costs outweigh the benefits of the research.
a second problem occurs with the limitations of generalising findings from animal studies to humans due to differences in physiology and the number/types of circadian rhythms , limiting ecological validity

Question 12

there have also been recorded cases where exogenous zeitgebers and endogenous pacemakers have failed to entrain or alter circadian rhythms , demonstrated by miles et al who reported the case of a man with a sleep wake cycle of 24.9 hours which

Answer 12

could not of been changed through use of stimulants or sedatives , therefore this suggests that the influence of exogenous and endogenous factors may be overestimated