biopsychology- circadian rhythms Flashcards
what are circadian rhythms?
biological processes which cycle in about 24 hours
what is an example of a circadian rhythm?
sleep-wake cycle
What are endogenous pacemakers?
internal (endo) mechanisms that govern biological rhythms e.g. pineal gland.
What are exogenous zeitgebers?
external (exo) cues that govern biological rhythms e.g. daylight influence the sleep- wake cycle.
What is the relationship between endogenous pacemakers and exogenous zeitgebers?
-all living organisms subject to biological rhythms governed by EP and entrained by EZ
-i.e. while sleep wake cycle is an EP its also affected by daylight an important EZ
What is the biological basis for the sleep-wake cycle?
-suprachiasmatic nucleus (SCN) is a major endogenous pacemaker in mammals that controls the sleep wake cycle (‘master clock’)
-It’s in the hypothalamus where optic nerves from the eye cross over
-gets stimulated by light that penetrates our closed eye lids
-the SCN (tiny bundle of nerve cells) then regulates our sleep/wake cycle
What role does the pineal gland play in the sleep wake cycle?
-SCN sends message to PG -which during night increases melatonin
-induces sleep
What is the role of melatonin in the sleep wake cycle?
-during night pineal gland increases the production of melatonin, induces sleep
-sunlight in morning stops melatonin production. increasing production of cortisol which increases wakefulness
What is the role of homeostasis in the sleep wake cycle?
-homeostasis is the maintenance of constant internal environment
-when individual awake for a long time it tells body that there’s a need for sleep bc of energy consumption
-homeostatic drive for sleep increases throughout day, reaching maximum in late evening when people fall asleep
Describe another circadian rhythm other than sleep.
body temp
-lowest (36°C) at 4:30am
-highest (38°C) around 6pm
-sleep occurs when core temp begins to drop, and body temp starts to rise in last few hours of sleep, promoting feeling of alertness
Describe Michel Siffre’s study
-spent several extended periods underground deprived of NATURAL light and sounds, but w/ food and water
-wanted to investigate the effect of no environmental cues on biological rhythms
Describe Michel Siffre’s findings
-absence of external cues significantly altered his circadian rhythm
-on return, believed it to be month earlier than it was
-suggests 24 hour sleep-wake cycle was increased by lack of external cues, making him believe one day was longer than it was leading him to think fewer days passed. although he had a regular biological rhythm still
conclusion from Siffre’s study
-implies circadian rhythms are mainly controlled my EP’s rather than EZ’s- but that EZ’s do have a significant influence
ao3: siffre’s study methodological issues
-lack of control as he used an artificial light so could have confounded results as other research has showed CR can be adjusted as a result of dim lighting. also he was researcher and p so experimenter bias could have been present
-reduces internal validity of results as EVs mean its hard to establish cause and effect
-however other research has found results similar to Siffre
Aschoff and Wever study
-55 p’s spent four weeks in a WWII bunker deprived of natural light
-all but one (who’s cycle extended to 29 hours) displayed a CR between 24-25 hours
Folkard er al. (1985)
-studied a group of 12 who lived in a dark cave for three weeks
-going to bed when clock was 11:45pm and waking at 7:45 am
-gradually sped up the clock to a 22 hour day
-only one p comfortably adjusted to new regime. suggests the existence of strong free-running circadian rhythms not controlled by EZs.
what does Siffre and the cave study from Aschoff and Wever show?
-the ‘natural’ sleep-cycle may be slightly longer than 24 hours but is entrained by EZs associated with our 24 hour day
ao3 circadian rhythms: temperature
-temp may be more important than light in CR
-Buhr et al (2010) found fluctuations in temp set the timing of cells in body and causes tissues and organs to become active/inactive. Buhr claimed that info ab light levels is transformed into neural messages that set the body’s temp
-body temp fluctuates on 24-hour circadian rhythm and even small changes can send powerful signals to our body clocks
-CR are controlled and affected by several different factors so more holistic approach may be preferable
ao3 of circadian rhythms: generalisability
-generalisations difficult to make
-studies often use small groups of p’s (e.g. Aschoff and Wever) or even one p (Siffre)
-p’s may not be representative of wider population so limits making meaningful generalisations. siffre observed internal clock ticked much more slowly at 60 than when younger.
-suggests even when same p involved, there are factors that may prevent general conclusions being drawn
ao3 of circadian rhythms: shift work
-application to shift work
-shift work creates desynchronisation of biological rhythms. Bovin et al. (1996) found shift workers experience a lapse of concentration around 6 am (a circadian trough) so accidents more likely
-research also suggests link w/ shift work and poor health- 3x more likely to develop heart disease (Knutsson 2003)
-so, research into the sleep/wake cycle may have economic implications in terms of how best to manage shift work
