Endogenous pacemakers and exogenous zeitgebers Flashcards
What is the main endogenous pacemaker influencing biological rhythms in humans?
Suprachiasmatic nucleus (SCN).
Where is the suprachiasmatic nucleus located in the brain?
Hypothalamus in both hemispheres.
How does the suprachiasmatic nucleus influence biological rhythms including the sleep wake cycle?
SCN receives info about light via optic nerve fibres. Even happens when eyes are shut. SCN acts as master clock using light levels to regulate bio rhythms including when to feel sleepy or awake.
How does the suprachiasmatic nucleus influence hormones to regulate biological rhythms?
Passes info about light and day length to pineal gland behind hypothalamus. Night - pineal increases melatonin production. Day - less production. Function as endogenous pacemakers but still determined by light levels.
What is the name for the process whereby an exogenous zeitgeber resets a biological clock?
Entrainment.
What does light influence in the body?
Sleep-wake cycle. Hormone secretion. Blood circulation.
Other than through optic nerves and the SCN, how may light be detected in the body?
Skin receptor sites such as the back of the knees.
What evidence is there for the back of the knees’ light reception?
Light shone on back of Ps knees successfully changed sleep-wake cycle by up to 3 hours.
How do social cues influence biological rhythms in babies?
When born - random sleep-wake cycle. After 16 weeks bio clocks set ‘entrained’ by meal and bed times from parents.
How can social cues influence adults?
Countering jetlag: meal and bed times of the local help to entrain bio clock to local time.
(AO3) What is a limitation of describing the SCN as the ‘master clock’?
Numerous circadian rhythms in in many organs and cells - not just SCN. Feeding mice in specific patterns was shown to alter circadian rhythms for up to 12 hours. Rhythm of SCN was unaffected. Suggests there are more complex influences influences on sleep-wake cycle.
(AO3) Why may the influence of exogenous zeitgebers on sleep-wake cycle be overstated/deterministic?
Individuals living in arctic (sun don’t set in Summer) show normal sleep patterns. Suggests exo zeit can have no influence in specific circumstances. More influences on cycles need to be considered. And Changing light levels does not necessarily lead to abnormal patterns.
(AO3) Outline limitations of the study into detection of light by skin receptors.
Findings not replicated + confounding variable. May have been some light exposure on Ps eyes (not just back of knees). Also light is not the only exogenous zeitgebers. Reduces validity + other influence need to be considered.
(AO3) Why may an interactionist approach may be more appropriate when identifying influences on the sleep-wake cycle?
Research tends to only look at the influence of exogenous zeitgebers or endogenous pacemakers. Therefore lacks external validity because the two clearly interact to determine sleep-wake patterns. E.g. Siffre only investigated endo and ignored exo (light).
