Endogenous pacemakers and exogenous zeitgerbers Flashcards
1
Q
what is an endogenous pacemaker?
A
- internal body clocks that regulate biological rhythms
- influence of superchiasmatic nucleus on sleep/wake cycle
1
Q
what is exogenous zeitgerber?
A
- external factors that effect or entrain our biological rhythms
- influence of light on our sleep/wake cycle
2
Q
what is the sleep/ wake cycle?
A
- a daily cycle of biological activity based on a 24 hour period
- influenced by regular variations in the environment e.g. night and day alternating
3
Q
What is the SCN?
A
- tiny bundle of nerves in the hypothallamus in each brain hemisphere
- primary endogenous pacemaker in mammals
- maintains circadian rhythms
4
Q
How does the SCN work?
A
- nerve fibres connected to the eye cross in the optic chasm on their way to the left/right VF
- lies above optic chasm
- receives info about light from this structure
- continues when eyes closed
5
Q
Animal studies on the SCN: DeCoursey Chipmunks
A
- DeCoursey destroyed the SCN of 30 chipmunks
- returned to natural habitat for 80 days
- their sleep/wake cycle disappeared
- most had been killed by predators
6
Q
Animal studies on the SCN: Ralph et al. mutant hamsters
A
- he bred ‘mutant’ hamsters with 20 hour sleep/wake cycles
- SCN cells from foetal tissue of mutant hamsters were transplanted into the brains of normal ones the cycle of the normal ones also changed to 20 hours
7
Q
The pineal gland and the SCN
A
- SNC passes info on day length and light that is received to the pineal gland
- this is an endogenous mechanism making the sleep/wake cycle
8
Q
The pineal gland melatonin
A
- during the night the pineal gland produces increased melatonin
- this induces sleep and reduces in time of wakefulness
- melatonin is also a causal factor for SAD
9
Q
How exogenous zeitgerbers work
A
- absence of external cues there’s a free running biological clock that controls our sleep/wake cycle
- this free running clock is ‘brought into line’ by environmental cues
10
Q
Endogenous pacemakers evaluation: limitation SCN can obscure other systems
A
- SCN may obscure other body clocks
- peripheral oscillators found in organs like lungs pancreas and skin
- influenced by SCN action but act independently
- changing feeding patterns in mice can alter the circadian rhythm of cells in the liver by up to 12 hours
- but SCN rhythm is unaffected
10
Q
Campbell and Murphys study on light
A
- light may be detected by skin receptors even when not received by the eyes
- 15 pp woken at diff times and a light pad was shone on the back of their knees
- produced deviation in the sleep cycles by up to 3 hours
- light is a powerful exogenous zeitgerber that doesnt necessarily rely on the eyes
10
Q
How light is a zeitgerber
A
- it can reset the bodys endogenous pacemaker, the SCN so plays a part in the sleep/wake cycle
- influences hormone release and blood circulation
10
Q
how social cues act as an exogenous zeitgerber: babies sleep/ wake cycles
A
- babies sleep/wake cycles is random
- at 6 weeks circadian rhythms begin
- ## at 16 weeks babies rhythms are entrained by schedules by parents
11
Q
how social cues act as an exogenous zeitgerber: research on jet lag
A
- adapting to local times for eating and sleeping is affective in training circadian rhythms and beating jet lag on long travels
