endogenous pacemakers and exogenous zeitgebers

Question 1

what is the SCN and where is it located?

Answer 1

a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain

Question 2

The SCN is one of the primary……

Answer 2

endogenous pacemakers

Question 3

what is the SCN influential in?

Answer 3

maintaining circadian rhythms e.g. sleep/wake cycle

Question 4

what is the optic chasm?

Answer 4

nerve fibres connected to the eye cross

Question 5

what does the SCN lie above?

Answer 5

the optic chasm

Question 6

what type of information does the SCN recieve?

Answer 6

information about light directly from this structure, this continues when our eyes are closed, enabling the biological clock to adjust to changing patterns of daylight whilst we’re asleep

Question 7

What did DeCoursey et al do?

Answer 7

destroyed the SCN connections in the brains of 30 chipmunks who were returned to their natural habit and observed for 80 days

Question 8

what happened to the sleep/wake cycle of the chipmunks?

Answer 8

it disappeared and by the end of the study a significant proportion of them had been killed by predators

Question 9

what did Ralph et al do?

Answer 9

bred ‘mutant’ hamsters with a 20-hour sleep/wake cycle

Question 10

What happened when SCN cells from the foetal tissue of mutant hamsters were transplanted?

Answer 10

the cycles of the second group defaulted to 20 hours

Question 11

what information does the SCN pass to the pineal gland?

Answer 11

information on day length and light

Question 12

what happens during the night?

Answer 12

the pineal gland increases melatonin

Question 13

what has melatonin been suggested as a casual factor in?

Answer 13

seasonal affective disorder

Question 14

endogenous pacemaker evaluation: obscure other body clocks

Answer 14

• research has shown that there are numerous circadian rhythms
• these peripheral oscillators are found in the organs including the lungs
• these are affluence by the actions of the SCN but also independently
• Damiola et al showed how changing feeding patterns in mice could alter the circadian rhythm cells in the liver by up to 12 hours whilst leaving the rhythm of the SCN unaffected
• suggests other complex influences on the sleep/wake cycle

Question 15

endogenous pacemaker evaluation: cannot be studied in isolation

Answer 15

• total isolation studies e.g. Siffre’s cave study are rare
• siffre also made use of artificial light which could have reset his biological clock every time he turned his lamp on
• in everyday life pacemakers and zeitgebers interact and it may make little sense to separate the two for the purpose of research
• suggests the more researchers attempt to isolate the influence of internal pacemakers the lower the validity of research

Question 16

what are exogenous zeitgebers?

Answer 16

external factors in the environment that reset our biological clocks through entrainment

Question 17

what can light reset?

Answer 17

the SCN and plays a role in the maintenance of the sleep/ wake cycle

Question 18

what does light have an indirect influence on?

Answer 18

key processes in the body that control functions such as hormone secretion and blood circulation