Biological rhythms Flashcards
Definition of circadian rhythms
One cycle takes approximately a day/24 hours
Examples of circadian rhythms
- Sleep wake cycle
- Body temperature
- Metabolic activity
- Hormones/NTs
Definition of infradian rhythms
One cycle takes longer than 24 hours
Examples of infradian rhythms
- Menstruation
- Hibernation
- SAD
Definition of ultradian rhythms
One cycle takes less than 24 hours
Examples of ultradian rhythms
- Feeding
- Stages of sleep
- Alertness
What are endogenous pacemakers
internal mechanisms that govern/influence the patterns of our biological rhythms e.g., The Pineal Gland, The Suprachiasmatic Nucleus (SCN)
The role of endogenous pacemakers in controlling the sleep wake cycle?
Internal body clock found in hypothalamus and is called the suprachiasmatic nucleus (SCN) (found in a small area in the hypothalamus) – this synchronises our sleep/wake circadian rhythm. The SCN receives light through the eyes (optic nerve). When light levels drop (at night), this information is received by the SCN causing it to fire impulses to pineal gland which then secretes melatonin which causes sleepiness. When light increases (daytime), melatonin levels fall making us more alert. Without light as a zeitgeber, the process ‘free runs’ to an average 25 hr cycle.
Positive evaluation of endogenous pacemakers - case study
There is case study evidence to support the role of endogenous pacemakers in regulating circadian rhythms like the sleep/wake cycle. For example, A French cave explorer, Michel Siffre spent 6 months in an underground cave in Texas in 1972, separated from natural light/dark cycles. This allowed him to investigate what happens when the bodily sleep/wake cycle is allowed to ‘free run’ away from exogenous zeitgebers. He was wired up so that various bodily functions could be recorded. He ate and slept whenever he wanted. At first his sleep/wake cycle was very erratic but settled down to a fairly regular pattern of between 25 and 30 hours, which is slightly longer than a 24-hour cycle. This supports the idea that EPs are important in regulating this rhythm, but also suggest that EZ play a role too.
Positive evaluations of endogenous pacemakers - scientific evidence
There is more scientific evidence to support the role of endogenous pacemakers in regulating circadian rhythms like the sleep wake cycle from animal studies. For example: Ralph et al (1990) Took the SCN from a ‘mutant hamster’ who had a circadian rhythm which had mutated to 20hrs. They transplanted the mutant SCN into the brains of normal adult hamsters. The normal hamsters took on the circadian rhythms of the mutant hamsters. This suggests objective laboratory-based research that enhances the scientific evidence about the idea of EP regulating circadian rhythms can be used to add credibility to the claim
Negative evaluation of endogenous pacemakers - case studies
One problem with evaluating the role of EPs in regulating circadian rhythms is that many studies into the effects on humans come from case studies. For example, the case study of Siffre was a one-off experience about a man who decided to live in a cave for 6 months to study the impact of EP’s, but this is not considered to be something that can be representative of all humans who live regular lives and are experiencing light and dark in everyday situations. This means what was found by Siffe is interesting, but the results cannot be generalised beyond the case itself therefore this research may not provide credible evidence for the role of EPs in controlling circadian rhythms.
Negative evaluation of endogenous pacemakers - animal studies
The use of animal studies may be problematic when considering the role of EPs in HUMAN circadian rhythms. For example, it can be claimed that research conducted on animals such as hamsters lacks biological continuity and so there was the experience of animals is not representative of human experiences humans would respond very differently to manipulations of their biological rhythms, not only because we are different biologically, but also because of the vast differences between environmental contexts. This makes research carried out on other animals unable to explain the role of endogenous pacemakers in the biological processes of humans. This means animal research findings into EP’s may not be able to be generalised to understand human circadian rhythms
What is an exogenous zeitgeber?
External stimuli/environmental cues that are responsible for resetting the biological clock which provides information about elapsed time and prompt changes in bodily activity and the patterns of biological rhythms e.g., temperature, noise, clocks
The role of exogenous zeitgebers in controlling the sleep/wake cycle
Light is the key zeitgeber in humans. It can reset the bodies main endogenous pacemaker -the SCN, and thus plays a role in the maintenance of the sleep/wake cycle. Light has an impact upon melatonin production and therefore sleep/wakefulness. Light also has an indirect influence on key processes in the body that control such functions as hormone circulation and blood circulation (but our focus is sleep).
Positive evaluation of exogenous zeitgebers - evidence to support
There is evidence to support the role of endogenous pacemakers and exogenous zeitgebers in regulating circadian rhythms like the sleep/wake cycle. For example, Vetter et al. (2011) conducted a longitudinal study over five weeks with volunteer participants who were either exposed to a ‘warm’ artificial light source or a ‘blue-enriched’ artificial light source, which was like daylight. Each participant was required to keep a daily record of their sleep patterns and wore equipment which measured how active they were during the daytime. It was found that participants in the first condition synchronised their circadian rhythm when dawn broke, which advanced every day, whereas those in the second group did not show this pattern and instead synchronised to their working hours at the office. This supports the idea that light is the dominant zeitgeber in the human sleep/wake cycle.
