Endo pacemakers + Exo Zeitgebers

Question 1

What are endogenous pacemakers?

Answer 1

Internal body clocks that regulate many of our biological rhythms such as influence of our SCN on sleep wake cycle

Question 2

What are exogenous zeitgebers?

Answer 2

External factors that affect or entrain our biological rhythms such as influence on sleep wake cycle

Question 3

Where is the SCN?

Answer 3

Tiny bundle of nerves in hypothalamus in each hemisphere of brain. It is one of primary endo pacemakers in humans. Nerve fibres connect to eye cross in an area called the optic chias , receives information about light directly from this structure. Continues when our eyes are closed to adjust to changing patterns of daylight whilst we are asleep.

Question 4

What re animal studies correlating with SCN?

Answer 4

Decoursey et al (2000) destroyed SCN connections in 3 chipmunk who then returned to natural state and observed for 80 days. The sleep wake cycle disappeared and most had been killed by predators.
Ralph et al (1990) bred mutant hamsters with a 20 hour SWC when SCN from tissue where implanted the normal hamsters had a 20 hour cycle

Question 5

What are two exogenous zeitgebers?

Answer 5

Light
Social cues

Question 6

How is light a key zeitgebers?

Answer 6

It resets the body’s main endo pacemaker, SCN and thus plays a role in maintenance of sleep wake cycle. Light has an indirect influence on hormone secretion and blood circulation.

Question 7

What did Campbell and Murphy do?

Answer 7

They demonstrated that light may be detected by skin receptors sites on body even when the same information isn’t received by the eyes. 15 p’s were woken at various times and the researchers shone alight pad at the back of their knees. They managed to produce a deviation in the p’s usual sleep/wake cycle of up to three hours.

Question 8

What are social cues effecting sleep?

Answer 8

• A new born adapts to parents meal and bed times
• Jet lag suggests adapting to local times for eating and sleeping entraining circadian rhythms.

Question 9

What is the evaluation of endogenous pacemaker research?

Answer 9

• Limitation of SCN research is that may obscure other body clocks
  -Limitation is endogenous pacemakers can’t be studies in isolation

Question 10

What is an evaluation of exogenous zeitgebers?

Answer 10

• They do not have the same effect in all environments
• Case study evidence challenges their role