endogenous pacemakers and the sleep wake cycle Flashcards
endogenous pacemaker definition
internal body clocks that regular many of our biological rhythms, such as the influence of the suprachiasmatic nucleus (SCN) on the sleep/wake cycle
sleep/wake cycle definition
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
what does SCN stand for
suprachiasmatic nucleus
what is the SCN
tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
SCN role
it is one of the primary endogenous pacemakers in mammalian species and is influential in maintaining circadian rhythms such as the sleep/wake cycle
what is the optic chiasm
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
where is the SCN
just above the optic chiasm
how does SCN receive information
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
who researched animal studies and the SCN (Chipmunks)
DeCoursey et al 2000
DeCoursey et al procedures for animal studies of the SCN
-destroyed the SCN connections in the brain of 30 chipmunks
-they were then returned to their natural habitat and observed for 80 days
DeCoursey et al findings for animal studies
-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)
who did research on animal studies and the SCN (hamsters)
Ralph et al 1990
Ralph et al animals studies procedure
-bred ‘mutant’ hamsters with a 20-hour sleep/wake cycle
Ralph et al animal studies findings
-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
how are the SCN and pineal gland linked
SCN passes the information on day length and light that receives to the pineal gland
where is the pineal gland
just behind the hypothalamus
what is the pineal gland
another endogenous mechanism guiding the sleep/wake cycle.
pineal gland hormone secretion
at night, the pineal gland increases production of melatonin
melatonin function
chemical that induces sleep and is inhibited during periods if wakefulness
limitation of endogenous pacemakers on the sleep/wake cycle - beyond the master clock
-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
limitation of endogenous pacemakers on the sleep/wake cycle - interactionist system
-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
evaluation of endogenous pacemakers on the sleep/wake cycle - ethics
-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
