ROLE OF EXOGENOUS & ENDOGENOUS IN SLEEP CYCLE & 1 OTHER BIO RHTYHM

Outline and evaluate research into the role of endogenous pacemakers and exogenous zeitgebers in the sleep/wake cycle and at least one other biological rhythm (24marks)

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ROLE OF EXOGENOUS & ENDOGENOUS IN SLEEP & 1 OBR

Endogenous pacemaker='biological clock'    Exogenous zeitgebers=external cues: light, social etc.

Interaction of proteins that regulate the biological clock of a fruit fly in a cycle (DARLINGTON): Morning- 2 proteins CLOCK & CYCLE bind -->prompts prod. PER & TIM --> PER & TIM render CLOCK & CYCLE inactive (as PER & TIM increase CLK & CYC decrease) --> as CLK & CYC decrease prod. of PER & TIM decreases (negative feedback) --> cycle starts again.. morning LIGHT prompting prod. CLK &CYC --> cycle takes 24 hours

High reliability b/c biological evidence provides objective, scientific evidence --> replicated many times.. different species, various forms--> H/W reductionist view: ignores most other factors .. looks at proteins in isolation --> basis of system 2 identifiable proteins (reductionist appropriate) but importance of light should be taken into account

Main endogenous pacemaker: Superchiasmatic Nucleus (SCN) in hypothalamus --> info. from light (optic nerve even eye shut) --> SCN responds to light levels & resets sleep wake cycle ... morning light wake up --> directs pineal gland: produces melatonin at night prompt us sleep

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ROLE OF EXOGENOUS & ENDOGENOUS IN SLEEP & 1 OBR II

Evidence SUPPORT SCN --> MORGAN: 'mutant' hamsters --> circadian rhtyhms 20hrs instead 24hrs --> transplanted SCNs to normal hamsters --> normal hamsters displayed mutant rhythms

SCN provides animals w/adaptive advantage (DeCoursey) --> 24 chipmunks SCN removed 20 still intact --> chipmunks w/removed SCN more vunerable to predators --> H/W study criticised unethical: chipmunks caused physical harm (killed by weasels) --> not justifiable for chipmunks to be used in such manner .. humans disregard animal suffer pain --> generalisability lackage findings from animal research not appropriate in most cases e.g. reptilian pineal glands in diff. place to human may have diff. function .. tests must be conducted on humans too

Research suggests we should study INTERACTION of endogenous & exogenous factors together not isolation --> SCN normally controls several rhythms but under certain circumstances body's seperate oscillators will desynchronise:KATE ALDCROFT cave --> after 25 days temp. rhythm 24hrs but sleep 30 hrs --> resynchronisation leads to jet lag-like symptoms --> variety of factors influential --> attempts made to make research less reductionist.. new techniques enable researchers study behaviour of cells, molecules & genes at once & produce complex picture of interaction

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E & E III

Exogenous zeitgebers re-set bio. clocks = entrainment --> Light dominant zeitgeber (sleep-wake cycle reset by light) --> early studies P's exposed to artificial lighting thought not to entrain bio. rhythms.. H/W Campbell & Murphy shifted circadian rhythm shine light back of P's knees.. demonstrates very little light & artificial light has effect

Many studies confounded by presence of artificial light--> Boivin dim lighting made diff. but bright light more effective --> Important Real World Application: sleeping w/constant artificial light bad (e.g. urban areas) --> could explain % increase in breast cancer industrialised areas

FASPS - linked to defect in one of the PER genes --> syndrome causes sleep a pm wake up 2am --> support bio rhythms biologically determined

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