Endogenous pacemakers & exogeneous zeitgebers

Question 1

What are endogenous pacemakers?

Answer 1

internal body clocks that regulate many of our biological rhythms such as the influence of the SCN on the sleep/wake

Question 2

What is the role and location of suprachiasmatic nucleus?

Answer 2

• tiny bundle of nerves located in the hypothalamus of each hemisphere
• SCN lies just above the optic chiasm and receives information about light
• primary endogenous pacemaker in mammalian species
• influential in maintaining circadian rhythms

Question 3

Outline Decoursey et al procedure and findings

Answer 3

• Decoursey et al destroyed SCN connections in the brains of 30 chipmunks
• then returned them to natural habitat for 80 days
• sleep wake cycle of chipmunks disappeared & by then significant proportion of them killed by predators because they were awake, vulnerable to attack

Question 4

Outline Martin et al procedure and findings

Answer 4

• bred ‘mutant’ hamsters with a 20 hour sleep/wake cycle
• When SCN cells transplanted from mutant hamsters into the brains of normal hamsters, their cycle defaulted to 20 hours

Question 5

What other endogenous pacemaker guides the sleep wake cycle & explain role?

Answer 5

• The SCN passes information on day length & light that it receives, to the pineal gland (pea-like structure behind hypothalamus)
• during night pineal gland increases production of melatonin- a chemical that induces sleep & inhibits during periods of wakefulness
  -causal factor of SAD

Question 6

What are exogeneous zeitgebers?

Answer 6

• external environmental factors that reset our biological clocks through a process known as entrainment e.g. light on the sleep-wake cycle

Question 7

What is the interaction between internal and external factors?

Answer 7

• without external cues, the free-running biological clock continues to ‘tick’ in a distinct cyclical pattern (Siffre study)
  The free running cycle is entrained by environmental cues

Question 8

What is a key zeitgeber in humans & role?

Answer 8

• light
• it can reset bodies main endogenous pacemaker, the SCN and thus plays a role in the maintenance of the sleep wake cycle

Question 9

Outline Campbell & Murphy’s procedure and findings

Answer 9

• demonstrated that light may be detected by skin receptors sites on the body even when the same information is not received by the eyes
• 15ps woken up at various times in the night & light pad shone on the back of their knees
• researchers produced a deviation in p’s usual s/w cycle of up to 3 hours in some cases
• light=powerful

Question 10

What is the influence of social cues on a babies sleep wake cycles?

Answer 10

• Babies sleep wake cycles are different
• at about 6 weeks circadian rhythms begin
• by 16 weeks babies rhythms have been entrained by schedules imposed by parents (mealtimes & bedtimes)

Question 11

What does research on jet lag suggest?

Answer 11

• that adapting to local times for eating & sleeping is an effective way of entraining circadian rhytmns

Question 12

What is a limitation of endogenous pacemakers (body clocks)

Answer 12

• SCN may obscure other body clocks
• Research has revealed that there are numerous circadian rhythms in many organ & cells
• peripheral oscillators are found in organs such as the lungs, pancreas & skin» - influence by actions of the SCN
• Damilola>demonstrated how changing feeding patterns in mice could alter the circadian rhythm of cells in liver by 12 hrs suggest other influences

Question 13

What are the ethical issues of research on sleep wake cycle?

Answer 13

• animals in Decoursey et al study were exposed to considerable risks when they returned to their natural habitat-killed
• animal studies with risk to animals difficult to justify

Question 14

What research support is there for the role of light?

Answer 14

• When Siffre returned from an underground stay with no clocks or light he believed the date to be a month earlier than it was
• which suggests that his 24 hour sleep wake cycle was increased by lack of external cues making him believe one day was longer than it was
• highlights impact of exogenous zeitgebers on bodily rhythms

Question 15

Why is EZ AND EP reductionist?

Answer 15

• behaviourists would suggest that bodily rhythms are influence by other people & social norms
• for example sleep occurs when it is dark because that is a social norm and it wouldn’t be socially acceptable for a person to conduct their daily routines during the night
• Criticised as it only considers a singular biological mechanism