Circadian Rhythms
- Created by: rhallett
- Created on: 11-10-15 10:18
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- Circadian Rhythms
- Approx. 24 hrs, inc sleep/wake cycle - 8 sleep 16 awake; regulated by the interaction of two things:
- Endogenous Pacemakers; biological 'clocks' mainly in the brain
- Main EP; small area in the hypothalamus named SCN. Neurons have an in built circadian firing patter which continues even when removed from the brain
- A direct pathway links the SCN to the retina of the eye and its activity is regulated by light. The SCN regulates the secretion of melatonin in the pineal gland.
- Melatonin is a hormone that helps induce sleepiness and is secreted during darkness; daylight suppresses the production of melatonin
- A direct pathway links the SCN to the retina of the eye and its activity is regulated by light. The SCN regulates the secretion of melatonin in the pineal gland.
- Main EP; small area in the hypothalamus named SCN. Neurons have an in built circadian firing patter which continues even when removed from the brain
- Exogenous Zeitgebers; external factors like light; reset our biological clocks
- In the morning, our clocks reset because the light causes the SCN to reduce melatonin production from the pineal gland
- Zeitgebers are required to 'entrain' our rhythm to a regular 24 hr cycle, without light the rhythm gets longer and out of sync with the environment
- In the morning, our clocks reset because the light causes the SCN to reduce melatonin production from the pineal gland
- Research; a lot shows the rhythms are regulation of EPs and EZS
- Michel Siffre; 6 months in cave in Texas, isolated from external stimuli, his sleep/wake cycle settled down to about 24.5 hrs - EPs alone can control circadian rhythms but EZs needed to keep them to a 24 hr cycle
- Case Study; difficult to generalise, he was exposed to dim light; could affect circadian rhythm as a result its unclear what this type of research shows
- Aschoff & Weaver; RPs in a war bunker, isolated from external cues, sleep/wake cycle settled down to about 25 hrs - EPs alone can control the S/W cycle
- More reliable than Siffre; a number of RPs in a more controlled and scientific environment
- AR; Morgan; bred mutant hamsters with rhythms of 20 hours, when transplanted their SCNs to normal hamsters they developed the same rhythm
- AR; Stephen & Zucker; destroyed the SCNs of rats and this disrupted their rhythms of drinking and activity; shows SCNs are important in animals
- Decoursey; destroyed chipmunks SCNs, rhythms disrupted - suggests animals have evolved to respond to zeitgebers as it is adaptive to have rhythms that are influenced by external factors; were noisy and active when they were vulnerable to predators like weasles
- AR; Stephen & Zucker; destroyed the SCNs of rats and this disrupted their rhythms of drinking and activity; shows SCNs are important in animals
- Michel Siffre; 6 months in cave in Texas, isolated from external stimuli, his sleep/wake cycle settled down to about 24.5 hrs - EPs alone can control circadian rhythms but EZs needed to keep them to a 24 hr cycle
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