3.10. Endogenous and Exogenous

Question 1

What do rhythms need doing to them?

Answer 1

They need tuning to keep in time with the external world.

Question 2

What is an endogenous pace maker?

Answer 2

• Mechanisms that govern internal biological rhythms
• SCN in the hypothalamus is the master time keeper-> it receives light from the optic chiasm, allowing our biological clock to adjust to changing patterns of light

Question 3

What was De Coursey’s study?

Answer 3

• Destroyed the SCN in 30 chipmunks, then returned them to their natural habitat
• Their sleep-wake cycle had disappeared, after 80 days, most had been killed by predators as they were awake at night and vulnerable to predators

Question 4

What does the pineal gland do?

Answer 4

Works with the SCN to release melatonin at night

Question 5

Strength: Morgan

Answer 5

• Morgan bred hamsters with SCNs of 20 hours
• The SCN from these were put into normal ‘24 hr’ hamsters
• Their sleep-wake cycle changed to 20 hours -> demonstrates the powerful influence of endogenous factors
• Animal research

Question 6

Strength: Siffre case study

Answer 6

• Siffre spent extended periods in a cage (2 months and 6 months) to study effects in endogenous pace makers -> he was deprived of sunlight and noise
• He found that his free running rhythm is 25 hours, not 24
• His sleep stayed regular (8 hrs)
• Endogenous pacemakers significantly influence biological rhythms

Question 7

What are exogenous zeitgebers?

Answer 7

• Environmental cues that help to regulate the biological clock
• Light is the key Zeitgeber for humans keeping them ‘in time’

Question 8

What did Campbell and Murphy conduct a study on?

Answer 8

• 15 ppts were awoken at various times by light being shone on the backs of their
• Led to a deviation in 3 hrs of their sleep-wake cycle
• Light is a powerful zeitgeber

Question 9

Other cues: temp, social cues etc

Answer 9

• It isn’t until 16 weeks babies’ rhythms become trained, therefore it’s very important to instil routines early on:
  * Dark and quiet at night
  * Noisy and bright

Question 10

Weakness: exaggeration

Answer 10

• Influence of exogenous zeitgebers may be exaggerated
• People who live in the Arctic Regions show normal patterns of sleep despite extended periods of light (24 hrs sometimes)
• Suggests sleep-wake cycles may be more influenced by endogenous pacemakers

Question 11

What happens in real life?

Answer 11

Endogenous and exogenous pacemakers work together