PAPER 2 - BIOPSYCHOLOGY - endogenous pacemakers and exogenous zeitgebers

Question 1

what are endogenous pacemakers?

Answer 1

maintains internal biological clocks in the brain

Question 2

what is an example of an endogenous pacemaker?

Answer 2

SCN in the master clock, controls the other body clocks and receives info about light levels - this keeps SCN’s circadian rhythm synchronised with daylight

Question 3

what are exogenous zeitgebers?

Answer 3

environmental events that influence the biological clock

Question 4

what are examples of exogenous zeigeber?

Answer 4

• light (resets body clock each day, keeps it on 24 hour cycle)
• social cues e.g. school

Question 5

what is photoentrainment?

Answer 5

when an organism’s biological clock, or circadian rhythm, synchronizes to daily cycles of light and dark in the environment

Question 6

what is the suprachiasmatic nucleus and where is it?

Answer 6

• cluster of nerve cells
• lies in hypothalamus of each hemisphere of the brain

Question 7

what influences the SCN in setting our body clock?

Answer 7

light levels

Question 8

whats the link between the SCN and melatonin?

Answer 8

SCN regulates the making and secreting of melatonin in pineal gland via interconnecting neural pathways

Question 9

what does melatonin do?

Answer 9

induces sleep by inhibiting the brain mechanisms that provide wakefulness

Question 10

what was the study by Morgan (1995)?

Answer 10

• aim: to investigate the importance of the SCN as an endogenous pacemaker in hamsters
• bred a strain of hamsters so they had abnormal circadian rhythms of 20 hours
• SCN neurones from these abnormal hamsters were then transplanted into brains of normal hamsters

Question 11

what were Morgans findings?

Answer 11

• hamsters displayed same abnormal circadian rhythm of 20 hours
• rather than maintaining abnormal circadian rhythm, the recipient hamsters then changed their circadian pattern back to 24 hours

Question 12

what do the findings by Morgan suggest about the role of the SCN?

Answer 12

confirms importance of circadian rhythms in animals

Question 13

what is a limitation of Morgans study?

Answer 13

• hard to generalise findings from animals to humans
• animals were exposed to considerable harm and risk when they returned to natural habitat

Question 14

what circumstances might result in other bodily rhythms becoming out of sync with each other and does this support or challenge the view that the SCN is the master clock?

Answer 14

• research has found that artificial light (from electronic devices etc) results in the disruption of circadian rhythms
• blue light disrupts circadian clock and supresses melatonin

Question 15

what is melanopsin?

Answer 15

a protein that travels along the optic pathway and SCN

Question 16

how do studies of blind people support the role of melanopsin and light perception?

Answer 16

• some blind people are still able to reliably entrain their circadian rhythms in response to light
• Skene and Andrendt estimate the vast majority of blind people who still have light perception normally have entrained circadian rhythms

Question 17

what further evidence is there for the role of exogenous zeitgebers from Burgess et al (2003)?

Answer 17

• found that exposure to a bright light prior to an east-west flight decreased the time needed to readjust to local time on arrival
• suggests light exposure prior to flights causes circadian rhythms to be partially re-entrained to local time

Question 18

what is the dominant zeitgeber for the SCN?

Answer 18

light

Question 19

how does the research by Vetter (2011) show light as the dominant zeitgeber for the SCN?

Answer 19

• demonstrated importance of light in the regulation of sleep-wake and activity-rest patterns of 2 groups of volunteers over 5 weeks
• one group remained in normal ‘warm’ light, other in artificial ‘blue’ light
• warm light group synchronised circadian rhythms each day
• results confirm that light is the dominant zeitgeber for SCN and effectiveness depends on its spectral composition