Endogenous pacemakers and exogenous zeitgebers

Question 1

What is an endogenous pacemaker?

Answer 1

Internal body clocks which regulate biological rhythms?

Question 2

What are exogenous zeitgebers?

Answer 2

External cues that may affect or entrain our biological rhythms

Question 3

What is the SCN?

Answer 3

• Suprachiasmatic nucleus
• A bundle of nerves located in the hypothalamus in each hemisphere of the brain- one of the primary endogenous pacemakers- maintains circadian rhythms,

Question 4

What was the DeCoursey et al squirrel study?

Answer 4

• Connections to SCN in 30 chipmunks severed and returned to their natural habitat and observed for 80 days
• A significant amount of the squirrels had been killed by the end since they were making noises during the night, making them easily tracked by predators

Question 5

What was the Ralph et al hamster study?

Answer 5

• He bred ‘mutant hamsters’ with 20 hour sleep/wake cycles

- SCN cells were transplanted into brains of normal hamsters and their cycles defaulted to 20 hours

Question 6

What is the pineal gland?

Answer 6

A ‘pea-like’ structure behind the hypothalamus which produces increased melatonin during the night

Question 7

What did the Campbell and Murphy study find in relation to light as a zeitgeber?

Answer 7

It was found that manipulation of light could produce deviations in a participant’s sleep/wake cycle by up to 3 hours and that the light still had effect when it was only received by the skin (not the eyes)

Question 8

What research is there to support the existence of endogenous pacemakers acting independently of the SCN?

Answer 8

Damiola et al (2000) demonstrated that altered feeding patterns could shift the circadian rhythms of a mouse’s liver without changing the rhythm of the SCN

Question 9

What are the problems of using animal studies as research support?

Answer 9

• Ethical issues (consent, right to withdrawal, protection from harm)
• Poor generalisation

Question 10

What research support is there to suggest zeitgebers may not have as much impact as previously suspected?

Answer 10

• Miles et al (1997) case study-young man blind from birth had a sleep/wake cycle of 24.9 hours, could not adapt to 24 hour cycle despite social cues and use of sedatives and stimulants
• In arctic regions, the sun does not set during the summer months- however, individuals who live there show normal sleep patterns

Question 11

What are some methodological issues with Campbell and Murphy’s study?

Answer 11

• The findings are yet to be replicated
• Light may not have been completely restricted from participants’ eyes
• Doesn’t account for zeitgebers other than light