Biopsychology: Enodgenous Pacemakers And Exogenous Zeitgebers

Question 1

What is an endogenous pacemaker

Answer 1

Internal body clocks that regulate many of our biological rhythms, such as the infleunce of the suprachaismatic nucleus (SCN) on the sleep wake cycle

Question 2

What is an exogenous zeitgeber

Answer 2

• external cues that may effect or entrain our biological rhythms
• e.g. the influence of light on the sleep wake cycle

Question 3

What is the suprachaismatic nucleus (SCN)

Answer 3

• tiny bundle of nerves located in the hypothalamus in each hemisphere of the brain
• one of the primary endogenous pacemakers in mammals
• influential in maintaining circadian rhythms such as the sleep/wake cycle
• receives info about light, which continues even when our eyes are closed

Question 4

Outline the animal study conducted by Decoursey on the SCN

Answer 4

• destroyed the SCN connections in the brains of 30 chipmunks who then retuned to their natural habitat and were observed for 80 days
• the sleep/wake cycle of the chipmunks disappeared + but the end of the study many were killed by predators

Question 5

Outline the animal study conducted by Ralph et al on the SCN

Answer 5

• bred ‘mutant’ hamsters with a 20 hour sleep/wake cycle
• when the SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of the 2nd group defaulted to 20 hours
• this emphasises the role of the SCN in establishing and maintaining the circadian sleep/wake cycle

Question 6

How is the pineal gland and melatonin related to the SCN

Answer 6

• SCN passes info on day length and light that it receives to the pineal gland
• during the night, the pineal gland increases production of melatonin (chemical that induces sleep and is inhibited during periods of wakefulness)

Question 7

Outline ‘light’ as a key zeitgeber in humans

Answer 7

• can reset the body’s main endogenous pacemaker (the SCN) + so plays a role in the maintenance of the sleep/wake cycle
• can also have an indirect influence on key processes in the body such as hormone secretion and blood circulation

Question 8

Outline research conducted into the effects of light as a zeitgeber

Answer 8

• Campbell and Murphy - showed light may be detected by skin receptor sites on the body even when the same info is not received by the eyes
• 15 ppts woken at various times + a light pad was shone on the backs of their knees
• researchers managed to produce a deviation in ppts usual sleep/wake cycle of up to 3 hours
• suggests light is a powerful zeitgeber that does not necessarily rely on the eyes to exert influence on the brain

Question 9

What is the sleep wake cycle like among infants

Answer 9

• the initial sleep/wake cycle in infants is random
• at around 6 weeks, the circadian rhythms begin and by 16 weeks,most babies are entrained
• research suggests the schedules imposed by parents dictate children sleep/wake cycle

Question 10

What are the three evaluation points for endogenous pacemakers and exogenous zeitgeber

Answer 10

-SCN not the complex influence on the sleep/wake cycle
- Ethics in animal studies
- influence of exogenous zeitgebers may be overstated

Question 11

Outline ‘SCN not the complex influence on the sleep/wake cycle’ as an evaluation point for endogenous pacemakers and exogenous zeitgebers

Answer 11

• research has revealed there are numerous circadian rhythms in many organs and cells in the body
• these are called peripheral oscillators
• although they are highly influenced by the actions of the SCN, they can act independently
• Damiola et al - showed changing feeding patterns in mice could alter the circadian rhythms of cells in the liver by up to 12 hours

Question 12

Outline ‘Ethics in animal studies’ as an evaluation point for endogenous pacemakers and exogenous zeitgebers

Answer 12

• animals exposed to considerable harm (especially in decoursey)
• also exposed to subsequent risk when returned to their natural habitat
• it is up for debate whether what we learn form these studies was worth their lives

Question 13

Outline ‘influence of exogenous zeitgebers may be overstated ’ as an evaluation point for endogenous pacemakers and exogenous zeitgebers

Answer 13

• miles et al - recounts story of a man, blind from birth with a circadian rhythm of 24.9 hrs
• despite exposure to social cues, his sleep/wake cycle could not be adjusted
• so, he had to take sedatives at night and stimulants in the morning to keep up with the world
• also studies of people in the arctic (where sun does not set in summer) show normal sleep patterns despite constant exposure to light