Endogenous pacemakers and exogenous zietgebers

Question 1

what are the types of endogenous pacemakers?

Answer 1

• suprachiasmatic nucleus
• animal studies and SCN
• pineal gland and serotonin

Question 2

what is an example of endogenous pacemakers?

Answer 2

• sleep/wake cycle

Question 3

where is the the suprachiasmatic nucleus located?

Answer 3

• suprachiasmatic nucleous (SCN) = tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain
• SCN lies just above the optic chiasm

Question 4

explain the SCN.

Answer 4

• one of the primary endogenous pacemakers in mammalian species
• influential in maintaining circadian rhythms such as the sleep/wake cycle
• nerve fibres connected to eye cross in an area called optic chiasm on their way to the left and right visual area of the cerebral cortex
• SCN receives info about light directly from this structure, and this continues when our eyes close
• enables the biological clock to adjust to changing patterns of daylight whilst we are asleep

Question 5

why are animal studies used in SCN?

Answer 5

• to show the influence of SCN

Question 6

who are the researchers involved in animal studies?

Answer 6

• DeCoursey et al
• Ralph et al

Question 7

what did DeCoursey et al do?

Answer 7

• destroyed the SCN connections in the brain of 30 chipmunks who were returned to their natural habitat and observed for 80 days
• sleep/wake cycle of chipmunks disappeared and by the end of the study a significant proportion of them had been killed by predators
• they were awake, active and vulnerable to attack when they should have been sleeping

Question 8

what did Ralph et al do?

Answer 8

• bred mutant hamster with a 20 hour sleep/wake cycle
• when SCN cells from foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of the second group defaulted to 20 hours

Question 9

explain the pineal gland and melatonin in the context of endogenous pacemakers.

Answer 9

• 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 (a chemical that induces sleep and is inhibited during period of wakefulness)
• melatonin has been suggested as a causal factor of seasonal affective disorder

Question 10

what are the exogenous zeitgebers involved in the sleep/wake cycle?

Answer 10

• light
• social cues

Question 11

explain light as an exogenous zeitgebers.

Answer 11

• resets the SCN so plays a role in the maintenance of sleep/wake cycle
• light is involved in hormone secretion and blood circulation

Question 12

who are the researchers involved in light?

Answer 12

Campbell and Murphy

Question 13

what did Campbell and Murphy do?

Answer 13

• demonstrated that light may be detected by skin receptor sites on the body even when the same info is not received by the eyes
• 15 ppts were woken at various time and a light pad was shone on the back of their knees
• researchers managed to produce a deviation in the ppts usual sleep/wake cycles of up to 3 hours
• suggests that light is powerful exogenous zietgeber that don’t rely on eyes to exert influence on brain

Question 14

explain social cues in the context of exogenous zietgebers?

Answer 14

• at about 6 weeks of age, the circadian rhythms begin and at about 16 week babies rhythms have been entrained by schedules imposed by parent, including adult-determined mealtimes and bedtimes

Question 15

what is the research involved in social cues?

Answer 15

• research of jet lag
• adapting to local time for eating and sleeping is an effective way of entraining circadian rhythms and beating jet lag when travelling long distances