Endogenous pacemakers and exogenous zeitgebers

Question 1

Endogenous pacemakers

Answer 1

Internal body clocks that regulate biological rhythms

Question 2

Exogenous zeitgebers

Answer 2

External factors that affect our biological rhythms

Question 3

Research on endogenous pacemakers

Answer 3

DeCoursey:
- Destroyed SCN connections in 30 chipmunks who were then returned to their habitat and observed
- Their sleep/wake cycle had disappeared
- A significant number of chipmunks had been killed by predators as they were awake and vulnerable to attack when they should’ve been asleep

Ralph:
- Bred mutant hamsters with 20 hour sleep/wake cycle
- SCN cells were taken and transplanted into normal hamsters
- The sleep/wake cycle of normal hamsters defaulted to 20 hours

Question 4

Research on exogenous zeitgebers

Answer 4

Campbell and Murphy:
- 15 p’s were woken at various times and a light pad was shone on the back of their knees
- Managed to produce a change in p’s usual sleep/wake cycle of up to 3 hours

Jet lag studies:
- Have shown that adapting to local times for eating and sleeping is an effective way of entraining circadian rhythms and beating jet lag when travelling

Question 5

Endogenous pacemakers - evaluation - strength

Answer 5

• Similar structures
• Existence of SCN and pineal gland of chipmunks and hamsters are similar to humans so generalisation can be made

Question 6

Endogenous pacemakers - evaluation - limitation

Answer 6

• Endogenous pacemakers can’t be studied separately
• In everyday life endogenous pacemakers and exogenous zeitgebers work together
• Suggests any attempts to study them separately lowers the validity of the research

Question 7

Exogenous zeitgebers - evaluation - limitation

Answer 7

• Don’t have the same effect in all environments
• e.g people who live in places like the arctic circle have similar sleep patterns all year round even though they spend around 6 months in total darkness
• Suggests sleep/wake cycles is primarily controlled by endogenous pacemakers that can override environmental factors e.g light