Biological Rhythms inc. consqeuences of disruptions

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©      Bio rhythm = any change in a bio activity that repeats periodically – synchronised with daily/monthly/annual cyclical changes in the environment

©      Ultradian rhythms = less than a day (feeding patters?)

©      Circadian rhythms = every day (daily sleep pattern)

©      Infradian rhythms = more than a day (28 day menstrual cycle)



©      Under usual light conditions, temp conditions etc, 24 hours – daily pattern of activities

©      ENDOGENOUS PACEMAKERS – ‘biological clocks’, built in, and so persist even when environmental stimuli are absent

-represent an inherited genetic mechanism

-however, not perfect, need some sort of environmental input to correct them each day

©      EXOGENUOUS ZEITGEBERS – ‘external time-givers’ environmental cues, eg light



©      = pea shape gland in brain, contains receptors that respond to external light, penetrating thin layer of skull, that lies above pineal gland (PG)

©      In turn, these light reflectors influence activity of neurons in PG

©      These neurons – have a natural rhythmic activity + also convert neurotransmitter serotonin into the hormone melatonin

©      Melatonin – then released into general circulation, which acts on many organs and glands – which seems to be responsible for rhythmic nature of many activities

©      E.g. acts on brainstem sleep mechanisms to help synchronize the phases of sleep/waking

©      ABRAHAM ET ALL 2000 – injections of melatonin = sleep in sparrows (extrapolation…)

©      Manufacture + release of melatonin – regulated by amount of light falling on PG, decreasing as light increases

©      BINKLEY 1979 – chickens wake/become active as dawn breaks, and melatonin secretion falls àGOOD EXAMPLE of how ENDOGENOUS PACEMAKERS interact with EXOGENUOUS ZEITGEBERS



©      Main bio clock – in Hypothalamus

©      SCN – neurons have a in-built CIRCADIAN rhythmic firing pattern

©      When SCN of rat is lesioned/damaged, CIRCADIAN rhythm inc sleeping + feeding patterns is totally ******

©      When SCN not lesioned/damaged – SCN regulated the manufacture + secretion of melatonin in PG via an interconnecting pathway

©      Another pathway connects retina (of each eye) to SCN – allowing amount of light falling on retina to influence the activity of SCN neurons + indirectly, release melatonin from PG à so link between light and melatonin production is maintained à recent research = light can get there without going through eyes

©      CAMPBELL + MURPHUY (1998) – light to the back of the knees = human participants – were able to shift circadian rhythm in body temp + melatonin secretion

©      PG in SCN function – jointly as ENDOGENOUS PACEMAKERS (/bio clock) in brain –mainly bodily rhythms – likely there are other structures involved in mainting their regularity à research – shown e.g. animals fed on regular basis – soon become active just before their feeding time à happens, even in the absence of


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