circadian rhythms - sleep wake

Circadian rhythms

• bio rhythms - repeated patterns of changes in the body regulated by an internal clock

• Circadian rhythm = about a day , e.g sleep wake cycle : once a day we sleep for extended period of time and then wake for an extended period of time

SCN, endo peacemakers and exo zeitgeber

• Endogenous peacemakers - endo - Greek for inside, genous = producing - internal body clock that regulates our bio rhythms e.g clock inside us deciding when we sleep or wake up

• Exogenous zeitgeber - exo = outside, zeitgeber = German for time giver - external cues influencing and resetting our bio internal clocks

• Scn = endogenous peacemake for sleep wake cycles , above the optic chiasm

• SCN = tiny cluster of nerve cells in hypothalamus - optic nerve transmits electrical impulses from eyes to brain

• The place where the optic nerves cross is called the optic chiasm

• Pineal gland also secretes melatonin which hells us fall asleep and its the SCN that regulates the pineal gland and thus our sleep

• Exo zeitgeber - one external cue that can influence our sleep wake cycles is light - the SCN (our internal clocks) receives info about light through our eyes and the optic nerve , the SCN can detect light even when eyes are shut

• When there’s less light, the SCN stimulates the pineal gland to produce more melatonin = falls to sleep (easier)

• When there’s more light melatonin productions reduces = helps us to feel awake

• Light can adjust our internal clocks Scn

• The time of sun rise and sun set changes each day so our internal clocks become out of sync - light esp early in morning helps us to recalibrate our internal clocks to outside world

Siffre research

• siffre spend 2 months underground in a cave without sunlight or clocks (time)

• Removal of exposure to natural light = he learnt about our internal bio clock, endo peacemaker

• He also wanted to see the effects of living without knowing what time was

• Whilst underground he monitored his body’s activity so that he recorded when he slept

• He found : despite a sense of natural daylight = maintained a regular sleep wake cycle of around 25 hours - e.g woke up and slept at regular fixed times - lost track of time - thought he had another month left when the study was done

• This research suggests : we have an internal bio clock controlling our circadian rhythm- sleep wake cycles

• Also suggests our sleep wake cycle is closer to 25 than 24 hours

• Also suggests it shows the need we have for exo zeitgeber like light to regulate our sleep wake cycle

Czeisler et al - with Eval

• Understood that bright light acted as an exo zeitgeber to the circadian rhythm but it was widely believed that the SCN (human circadian pacemaker) was not affected by ordinary indoor artificial light :

• Siffre had artificial light in his cave for 2 months where he read, studied etc - this artificial light could’ve influenced his sleep wake cycle

• Weakness - this study undermines the findings of self isolation studied like siffre in terms of the length of the sleep wake cycle as they had artificial light which may have influenced and reset their circadian rhythms

• Strength - practical apps - beyond the sleep wake cycle there are other many examples within the body of circadian rhythms such as body temp, digestion, hormone secretion - all affected by time of day: chronotherapeutics - study o chow timing affects drug treatments e.g cancer patients in the day are given an intravenous medication to kill cancerous cells - appears to be an optimal time to deliver medication helping to fight cancer and limiting harm to patient - shows importance of circadian rhythms and impact on human life