endogenous pacemakers and exogenous zeitgebers

Question 1

Endogenous pacemakers

Answer 1

Internal body clocks that regulate many of our biological rhythms, such as the influence of the suprachiasmatic nucleus SCN on the sleep/wake cycle

Question 2

Exogenous zeitgebers

Answer 2

External factors that affect or entrain our biological rhythms, such as the influence of light on the sleep/wake cycle

Question 3

Sleep/wake cycle

Answer 3

A daily cycle of biological activity based on a 24-hour period (circadian rhythm) that is influenced by regular variations in the environment, such as the alternation of night and day

Question 4

The suprachiasmatic nucleus

Answer 4

SCN receives information about light from optic chiasm

Question 5

Animal studies and the SCN

Answer 5

Sleep/wake cycle disappeared when SCN destroyed (DeCoursey et al)
SCN transplanted from mutant hamsters with 20-hour sleep cycle (Ralph et al)

Question 6

The pineal gland and melatonin

Answer 6

The SCN passes information to the pineal gland that controls melatonin

Question 7

Light

Answer 7

Light shone on back of knees changed rhythm by up to three hours (Campbell and Murphy)

Question 8

Social cues

Answer 8

Babies’ rhythms and jet lag are entrained by bedtimes and mealtimes

Question 9

Beyond the master clock - endo

Answer 9

• May obscure other body clocks
• Other body clocks (peripheral oscillators) eg circadian rhythm of liver cells in mice altered but SCN unaffected (Damiola et al)
• Suggest other complex influences influences on the sleep/wake cycle

Question 10

Interactionist system - endo

Answer 10

• Endogenous pacemakers cannot be studied in isolation
• Research looks at pacemakers/zeitgebers in isolation, approach lacks validity
• The more researcher attempt to isolate the influence of internal pacemakers, the lower the validity of the research

Question 11

Ethics - endo

Answer 11

• Mammals used to study sleep/wake cycle, however causes many to die (e.g. Decourset et al’s chipmunks)

Question 12

Environmental observations - exo

Answer 12

• Not same effect in all environments
• Ezs do not have same effect on people who live in darkness in summer and little light in winter (e.g. Inuit peoples in Arctic circle)

Question 13

Case study evidence - exo

Answer 13

• Evidence challenges the role exogneous zeitgebers
• Man blind from birth with sleep/wake cycle, of 24.9 hours, could not adjust despite social cues, e.g. mealtimes (Miles et al)

Question 14

Age-related insomnia - exo

Answer 14

• Poorer quality sleep when older
• Poorer quality sleep as people age, may be natural changes in biological rhythms (Duffy et al) or exogenous factors e.g. activity/exposure to natural light during day (Hood et al)