Biological rhythms
- Created by: Fredcatley
- Created on: 22-10-18 17:30
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- Biological rhythms
- Endogenous pacemakers
- Definition
- Internal mechanisms that govern biological rhythms (circadian sleep/wake cycle).
- Example
- Biological clock left to its own devices without the influence of external stimuli (light).
- Definition
- Exogenous zeitgebers
- Definition
- External changes in the environment responsible for resetting the biological clock of an organism.
- Example
- Effect of daylight: we feel drowsy when its night-time and alert during the day.
- suprachiasmatic nucleus (SCN)
- Endogenous pacemakers
- Definition
- Internal mechanisms that govern biological rhythms (circadian sleep/wake cycle).
- Example
- Biological clock left to its own devices without the influence of external stimuli (light).
- Definition
- Main endogenous pacemaker (master clock)
- Controls other biological rhythms, as it links to other areas of the brain responsible for sleep and arousal.
- The SCN also receives information about light levels (an exogenous zeitgeber) from the optic nerve.
- Sets the circadian rhythm so that it is in synchronisation with the outside world, e.g. day and night.
- Example of how melatonin works.
- 1. Low levels of light (retina)
- 2. Melanopsin (protein in eye) carries signal to SCN.
- 3. Axon pathway to pineal gland.
- 4. Leads to an increase in the production of melatonin (at night).
- 5. Helps to induce sleep.
- 4. Leads to an increase in the production of melatonin (at night).
- 3. Axon pathway to pineal gland.
- 2. Melanopsin (protein in eye) carries signal to SCN.
- 1. Low levels of light (retina)
- Endogenous pacemakers
- Studies
- Aschoff and Wever (1976)
- Procedure
- A group of pp's spent 4 weeks in a WW2 bunker, which was deprived of natural light.
- Aim
- Examine how light influences free-running biological rhythms.
- Findings
- All but one pp displayed a circadian rhythm between 24 and 25 hours.
- Suggests that natural sleep/wake cycle is about 24 hours but is influenced by exogenous zeitgebers (no.of daylight hours).
- All but one pp displayed a circadian rhythm between 24 and 25 hours.
- Procedure
- Siffre (1970s)
- Procedure
- Siffre spend long periods in a dark caves: Alps and Texas.
- Findings
- In each case study Siffre's free-running circadian rhythm settled down to 25 hours.
- Suggests that our internal body clock is very effective in sticking to a 24 hour day.
- In each case study Siffre's free-running circadian rhythm settled down to 25 hours.
- Aim
- Examine effects of free-running biological rhythms.
- Procedure
- Aschoff and Wever (1976)
- Definition
- Endogenous pacemakers
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