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 cycle

Question 2

What is the role and location of suprachiasmatic nucleus?

Answer 2

• primary endogenous pacemaker in mammalian species
• tiny bundle of nerves located in the hypothalamus of each hemisphere
• SCN lies just above the optic chiasm and receives information about light from this structure which influential in maintaining circadian rhythms e.g. sleep wake cycle

Question 3

What was Ralph et al procedure and findings?

Answer 3

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

Question 4

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

Answer 4

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

Question 5

What are exogeneous zeitgebers?

Answer 5

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

Question 6

What is a key zeitgeber in humans & role?

Answer 6

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

Question 7

What was Campbell & Murphy’s procedure and findings?

Answer 7

• demonstrated that light may be detected by skin receptors sites on the body even when the same information is not received by the eyes
• woke up p’s at various times in the night & light pad was 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 & does need to rely on eyes to exert its influence

Question 8

What is another exogeneous zeitgeber that influences the sleep wake cycle and explain how?

Answer 8

• social cues
• new born sleep wake cycles are random
• at about 6 weeks circadian rhythms begin
• by 16 weeks babies rhythms have been entrained by schedules imposed by parents (mealtimes & bedtimes)

Question 9

What does research on jet lag suggest?

Answer 9

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

Question 10

What is a strength of SCN research?

Answer 10

• research to support
• influence of SCN has been demonstrated in studies involving animals
• Decoursey et al destroyed SCN connections in the brains of chipmunks who were then returned to natural habitat & observed
• sleep wake cycle of chipmunks disappeared & by end of study a significant proportion of them had been killed by predators because they were awake, vulnerable to attack
• importance of SCN

Question 11

What is a counterpoint to research on the SCN?

Answer 11

• SCN research may obscure other body clocks in our bodies
• e.g. there are many organs which have body clocks which are known as peripheral oscillators which have an effect on the sleep wake cycle
• suggest other complex influences on the sleep wake cycle which are ignored

Question 12

What is a strength of the role of light?

Answer 12

• research to support
• 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 13

What is a counterpoint to research to support role of light?

Answer 13

• limitation of studies which investigate exogenous zeitgeber of light is that they present a confounding variable of artificial light
• as this variable is not controlled, this casts doubt of the validity of the results from these studies

Question 14

What is a limitation of research into EP’s?

Answer 14

• can be considered reductionist
• behaviourists would suggest that bodily rhythms are influenced 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 that affects the s/w cycle
• perhaps the effects should not be studied in isolation as they interact > holistic