endogenous pacemakers and exogenous zeitgebers

Question 1

AO1: Endogenous pacemakers

Answer 1

Internal mechanisms that governs biological rhythms e.g. circadian sleep wake cycle. Although they are internal they can be effected by external factors e.g. light.

Most important is the suprachiasmatic nucleus, in the hypothalamus, and is linked to the pineal gland.

animal study example:
destroyed SCN connection in brain of 30 chipmunks, they then returned to their natural habitat and were observed for 80 days. The sleep/wake cycle of chipmunks had dissapeared.

Question 2

AO1: exogenous zeitgebers.

Answer 2

Influence biological rhythms through environmental events e.g. social cues (meal times and social activities), most important is light

SNC contains receptors that are sensitive to light and this external cue is used to synchronise the bodies internal organs & glands.

Melenopsin effected by light

Light study:
Woken at various times of night by researcher and light pad was shone on back of knees. This managed to produce a deviation in participants usual sleep wake cycle of up to 3 hours.

Question 3

AO3: strength of endogenous pacemakers- research studies showed the importance of SCN (hamster)

HOWEVER, low population validity

Answer 3

P: research studies showed the importance of SCN
E: researchers bred hamsters so that they had circadian rhythms of 20 hours instead of 24 hours.
E: SCN neurons from abnormal hamsters were transplanted into the brains of normal hamsters, which displayed the same 20 hour circadian rhythm.
L: shows the trasnplanted SCN had imposed its pattern onto the hamster. Demonstrates how endogenous pacemakers are important

HOWEVER, used hamsters so can’t generalise to target population, low population validity

Question 4

Strength: research support for exogenous zeitgebers (cave man)

HOWEVER, case study

Answer 4

P: research support for exogenous zeitgebers
E: cave guy returned from an underground stay with no cocks or light, he believed the date was a month earlier.
E: suggests that his 24 hour sleep wake cycle was increased by the lack of external cues, making one believe on day was longer than it was.
L: highlights impact of external factors on bodily rhythms
HOWEVER, was a case study so cant be generalised as only one person

Question 5

strength of exogenous zeitgebers: research support for role of melanopsin

Answer 5

P: research support for role of melanopsin
E/E: researchers claimed majority of blind people who still have some light perception have normal circadian rhythms, whereas those without any light perception show abnormal circadian rhythms.
L: demonstrates importance of exogenous zeitgebers as a biological mechanism and their impact on biological circadian rhythms.

Question 6

Limitation-is biologically reductionist

Answer 6

P: both are biologically reductionist
E: behaviourist approach would suggest that bodily rhythms are influenced by people and social norms.
L: criticised for being reductionist.