endogenous pacemakers and the sleep wake cycle

Question 1

endogenous pacemaker definition

Answer 1

internal body clocks that regular many of our biological rhythms, such as the influence of the suprachiasmatic nucleus (SCN) on the sleep/wake cycle

Question 2

sleep/wake cycle definition

Answer 2

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 3

what does SCN stand for

Answer 3

suprachiasmatic nucleus

Question 4

what is the SCN

Answer 4

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

Question 5

SCN role

Answer 5

it is one of the primary endogenous pacemakers in mammalian species and is influential in maintaining circadian rhythms such as the sleep/wake cycle

Question 6

what is the optic chiasm

Answer 6

nerve fibres connected to the eye cross in the optic chiasm on their way to the left and right visual area of the cerebral cortex

Question 7

where is the SCN

Answer 7

just above the optic chiasm

Question 8

how does SCN receive information

Answer 8

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

Question 9

who researched animal studies and the SCN (Chipmunks)

Answer 9

DeCoursey et al 2000

Question 10

DeCoursey et al procedures for animal studies of the SCN

Answer 10

-destroyed the SCN connections in the brain of 30 chipmunks
-they were then returned to their natural habitat and observed for 80 days

Question 11

DeCoursey et al findings for animal studies

Answer 11

-sleep/wake cycle of the chipmunks disappeared
- by the end of the 80 days, a significant proportion had been killed by predators (this is presumed to be because they were awake, active and vulnerable to attack when they should have been asleep)

Question 12

who did research on animal studies and the SCN (hamsters)

Answer 12

Ralph et al 1990

Question 13

Ralph et al animals studies procedure

Answer 13

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

Question 14

Ralph et al animal studies findings

Answer 14

-when the SCN cells from the foetal tissue of mutant hamsters were transplanted into the brains of normal hamsters, the cycles of the second group defaulted to 20 hours

Question 15

how are the SCN and pineal gland linked

Answer 15

SCN passes the information on day length and light that receives to the pineal gland

Question 16

where is the pineal gland

Answer 16

just behind the hypothalamus

Question 17

what is the pineal gland

Answer 17

another endogenous mechanism guiding the sleep/wake cycle.

Question 18

pineal gland hormone secretion

Answer 18

at night, the pineal gland increases production of melatonin

Question 19

melatonin function

Answer 19

chemical that induces sleep and is inhibited during periods if wakefulness

Question 20

limitation of endogenous pacemakers on the sleep/wake cycle - beyond the master clock

Answer 20

-SCN may obscure other body clocks
-research has revelled that there are numerous circadian rhythms in many organs and cells in the body. these peripheral oscillators are found in the organs including the lungs, pancreas and skin. these are influenced by the actions of the SCN, but can also act independently. Damiola et al 2000 demonstrated how changing feeding patterns in mice could alter the circadian rhythms of 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 21

limitation of endogenous pacemakers on the sleep/wake cycle - interactionist system

Answer 21

-endogenous pacemakers cannot be studies in isolation
-total isolation studies, such as Siffre’s cave study are extremely rare. Siffre’s study also used 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 purpose of research –> suggests the more researchers attempt to isolate the influence of internal pacemakers, the lower the validity of the research

Question 22

evaluation of endogenous pacemakers on the sleep/wake cycle - ethics

Answer 22

-animals studies of the sleep/wake cycle are justifies because there are very similar mechanisms at work across species. the existence of an SCN and pineal gland in the brains of, say, chipmunks and hamsters means that generalisations can be made to the human brain. as mammalian bran has similar structures
-there are ethical problems with the research. the animals in DeCoursey at al study were exposed to risk when returned to their natural habitat and most died as a result of this