Endogenous pacemnakers & Exogenous Zeitgebers Flashcards
A01
Outline endogenous pacemakers & sleep/wake cycle
Endogenous pacemakers are internal body clocks that regulate our biological rhythm such as influence of suprachiasmatic nucleus on sleep wake cycle but can be affected by external enviroment e.g changes in light
* SCN its a endogenous pacemaker ( & bodys method for inducing sleep)
* The suprachiasmatic nucleus is vital in maintaining our circadian rhythms e.g the sleep/wake cycle
A01
Biological rhythms
Biological rhythms are influenced by 2 things:
* Internal body clocks( endogenous pacemakers)
* External cues in the enviroment ( Exogenous zeitgebers)
A01
Outline the suprachiasmatic nucleus-(its an endogenous pacemaker)
SCN is located in the hypothalamus in each hemisphere
vital in maintitaing circadian rhythms e.g sleep wake cycle
SCN recieves info about light via the optic chiasm
When light is detected by SCN it sends light to pineal gland-stopping production of melatonin
even when eyes shut SCN gets info on light from optic nerve
enabling biological clock to adjust to changing patterns of daylight whilst asleep
as light can penetrate eyelids & special photoreceptors in eye tranfer light signals to SCN
dont have to revise:
Increased melatonin release triggers decreased serotonin
production, creating feelings of sleepiness during the night time, where there is little exposure to light.
Conversely, during the daytime, when there is high exposure to light, the SCN triggers the
pineal gland to release less melatonin over a longer period of time, resulting in increased serotonin
production, creating feelings of wakefulness
A01
The pineal gland & Melatonin
The SCN passes info on day length & light to the pineal gland. During the night the pineal gland increases the production of melatonin ( a chemical that induces sleep & is inhibited during wakefulness)
A01
Outline animal studies & SCN
DeCoursey
The influence of SCN -demonstrated in animal studies
DeCoursey et al destroyed the SCN connections in brains of 30 chipmunks,who were then returned to natural habitat, observed for 80 days
findings: The sleep wake cycle of the chipmunks disappeared by end of study , signif proportion of chipmunks killed by predators ( because they were awake & vulnerable to attach when should of been sleeping)
Outline exogenous zeitgebers
Exogenous zeitgebers are external factors in enviroment reset our biological clock through process called entrainment
Light-exogenous zeitgeber, it can reset the bodys main endogenous pacemaker , the SCN, thus light plays role in maintenance of sleep/wake cycle
A01
Outline Campbell & Murphys study-Exogenous Zeitgebers
They demonstrated that light may be detected by skin receptor sites on the body even when the same info is not recieved by the eyes
15 p were woken up at various time & a light pad was shown on the back of their knees
the researcher managed to produce a deviation in the P usual sleep wake cycle of up to 3 hours
shows light is powerful exogenous zeitgeber that doesnt always rely on the eyes to exert its influence on brain
A01
Social cues-exogenous Zeitgebers
Social cues also acts as exogenous zeitgebers e.g
* The timing of meals
* work schedules
* exercise sessions
People can compensate when there is a lack of natural light using these social cues
in infants , the sleep wake cycle is random
at 6 weeks the circadian rhythm begins
by 16 weeks babies rhythms are entrained by schedules imposed by parents e.g adult-determined meals & bedtimes
research suggests by adapting to local time schedules for eating & sleeping is effective way of entraining circadian rhythms
A01
Animal studies-Ralph et al
Ralph bred mutant hamsters with 20 hour sleep wake cycle - the hamsters with tau mutation had a circadian rhythm of 20 hours compared with 24 hours for normal hamsters
when SCN from normal hamsters were transplanted into brains of tau mutation hamsters , hamsters gained sleep wake cycle of 24 hours
normal hamsters gained 20 hour cycle when given SCN from mutant hamsters
both studies demonstrate role of SCN in establishing & maintaining circadian sleep wake cycle
A03
ETHICS involved in animal studies (DeCoursey et al)
& difficult to generalise
The animals were exposed to considerable harm & risk when they were returned to natural habitat
thus breaching the BPS ethical guideline of protection from psychological & physical harm.
a cost-benefit analyses would have to be conducted to assess whether ethical costs outweigh benefits of an improved understanding of exogenous zeitgebers & endogenous pacemakers
- research Difficult to generalise because of its use of chipmunks, humas would respond diff to manipulations of their biological rhythm, due to diff in biology & diff in enviromental contexts
A03
The influence of SCN is overestimated
numerous circadian rythms in organs & cells-peripheral oscillators
Damiola -researcher
Limitation
research found their is numerous circadian rhythms in organs & cells of the body , called peripheral oscillators-& found in adrenal gland,pancrease, liver lungs
- although peripheral clocks are influenced by actions of SCN, they can act independently
- Damiola et al demonstrated how changing feeding patterns in mice can alter their circadian rhythms of the cells in liver up to 12 hrs, whilst leaving circadian rhythm of SCN unaffected
suggets theres other compex influences on sleep wake cycle aside from SCN
A03
The influence of exogenous Zeitgebers overstated-Miles
Limitation
theres researched recorded cases where exogenous zeitgebers and endogenous pacemakers
have failed to entrain or alter circadian rhythms, e.g Miles et al (1977) reported the case of a man with a sleep-wake cycle of 24.9 hours, which could not be changed through use of stimulants or sedatives.
suggests that influence of exogenous & endogenous factors may be overestimated
