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FlashCards por chloe.brandon, atualizado more than 1 year ago
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Criado por chloe.brandon
mais de 8 anos atrás
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| Questão | Responda |
| What are endogenous pacemakers? | Internal body clock that manages biological rhythms |
| What is an example of an endogenous pacemaker? | The Superchiasmatic Nucleus (SCN) |
| Where does the SCN lie? | In the hypothalamus, just above the place where the optic nerves from each eye cross over |
| What does the SCN do? | obtains information about light from the eye via the optic nerve. This even happens when our eyes are shut because light penetrates the eyelids. |
| What happens if our endogenous clock is running slow (sun rises earlier than the day before) | morning light automatically shifts the clock ahead |
| What is the SCN? | a pair of structures, one in each hemisphere of the brain, each of these divided into a ventral and dorsal SCN. The ventral is relatively quickly reset by external cues whereas the dorsal SCN is much less affected by light and therefore more resistant to being reset (Albus et al 2005) |
| What role does the SCN have in the sleep-wake cycle? | light enters the eye and a message is sent via the optic nerve to the SCN. The SCN then sends a message to the pineal gland to reduce melatonin levels in order for you to wake up. When the eye sense darkness the SCN send a message to the pineal gland to release melatonin to induce sleep. |
| What research evidence is there for the role of the SCN? | Morgan (1995) bred 'mutant' hamsters so they had circadian rhythms of 20 hours instead of 24 hours. They then transplanted their SCNs into normal hamsters. The normal hamsters then displayed the mutant rhythm. |
| Are there any issues with this study? | Ethical issues could be raised about deliberately trying to change the natural rhythm of the hamsters as they didn't know about the effects and the hamsters all died. Also the physiological/biological make-up of hamsters is different therefore we cannot be sure that the human body would react in the same way - testing this would be unethical. |
| Are there any positives that come from animal research? | Using animals enables us to complete experiments that we wouldn't otherwise be able to do on humans. The research stated with mutant hamsters could potentially provide us with theories as to how our SCNs work. |
| What is another endogenous pacemaker? | Pineal gland and melatonin |
| What does the pineal gland do once it receives a message from the SCN that it is dark? | increases the production of melatonin which induces sleep by inhibiting the brain mechanisms that promote wakefulness |
| Where does the pineal gland lie in birds and how does it function? | Just below the bone of the skull. It is directly regulated by light, light inhibits the production of melatonin. |
| What do many lizards have? | A 'third eye' which is actually a small opening in the skull which enables light to directly reach the pineal gland. |
| Do the body's oscillators desynchronise? | Under normal circumstances the central oscillator (SCN) coordinates all other body rhythms, but in certain circumstances the body's separate oscillators desynchronise. |
| Is there a research example to support this? | Kate Aldcroft spent time in a cave. When she emerged her body temperature had kept a 24 hour cycle where as her sleep-wake cycle had increased to 30 hours. These rhythms had desynchronised. (Folkard, 1996) |
| What symptoms does this de-synchronisation lead to? | symptoms similar to jet lag - which is essentially a state of desynchronised rhythms. |
| What is an Exogenous Zeitgeber? | external environmental factors than have an influence on our endogenous pacemakers |
| What is the process of resetting the biological clock with exogenous zeitgebers? | entrainment |
| What is the opposite of entrainment? | free-running |
| What is an example of an exogenous zeitgeber? | light |
| What effect does light have on our endogenous pacemakers? | it is the dominant zeitgeber and can reset the body's main pacemaker (SCN). It can also reset the other oscillators located throughout the body because the protein CRY which is part of the 'protein clock' is light-sensitive. |
| What might this explain? | Why Campbell and Murphy (1998) found that if you shine light on the back of participants' knees this shifted their circadian rhythms. |
| Will any lighting act as a zeitgeber? | Initially in early studies (Siffre, Aschoff and Wever) participants were exposed to artificial lighting but it was thought that this would not be enough to entrain rhythms. However Campbell and Murphy proved that it is effective by shining light on the back of participants' knees |
| What has recent research shown? | Bovin et al (1996) found that circadian rhythms can be entrained by ordinary dim lighting, although bright light was more effective |
| What does this prove? | artificial lighting in general does have an effect |
| If dim lighting does reset the biological clock, then the fact that we live in an artificially lit world must have negative consequences? | Stevens (2006) suggests that artificial lighting disrupts circadian rhythms and subsequently disrupts melatonin production and may explain why women in industrialised (and well lit) societies are more likely to develop breast cancer. |
| Name a second exogenous zeitgeber | Social Cues |
| What are examples of social cues? | We eat meals at socially determined mealtimes Go to bed and wake up at times designated as appropriate for our age |
| What do our daily rhythms appear to be controlled by? | social convention not internal biology |
| We know that light is the dominant zeitgeber but all parts of the body produce their own oscillating rhythms some of which are not reset by light. Give an example. | The zeitgeber for cells in the liver and heart is likely to be mealtimes because these cells are reset by eating. |
| Name a third exogenous zeitgeber. | Temperature |
| What effects the setting of the circadian rhythms in cold blooded animals? | variation in external temperature |
| What temperature signals what? | cold temperature signals time for reduced activity whereas warm temperature signals time for increased activity (sleep-wake) |
| What did Buhr et al, 2010 find? | In warm blooded animals such as humans, the daily changes in body temperature are governed by their own circadian clock and these temperature changes entrain other circadian rhythms. |
| What does the basis of the circadian clock rely on? | Interactions between certain proteins |
| What does this reaction create? | the 'ticking' of the biological clock |
| Who identified such proteins and where? | Darlington et al (1998) in the fruit fly |
| Which two proteins bind together in the morning? | CLOCK and CYCLE (CLK-CYC) |
| What do these two proteins produce once they've joined together? | two other proteins: PERIOD and TIME (PER-TIM) |
| What does PER-TIM have the effect of? | rendering the CLK-CYC proteins inactive, so that as PER-TIM increases, CLK-CYC decreases and then subsequently PER-TIM decreases too (negative feedback) |
| How long does this loop take? | 24 hours, giving us our biological clock |
| Where is this protein mechanism present? | In the SCN (central oscillator) and other cells throughout the body (peripheral oscillators) |
| Do the proteins vary from animal to animal? If so, what are the human pairs? | CLOCK-BMAL1 and PER-CRY (BMAL1 and CRY are also proteins) |
| Are the endogenous and exogenous systems divided? | There isn't a clear division between the two systems. Aside from total isolation experiments, the running of the biological clock is a combined endogenous-exogenous exercise. |
| When the biological system fails it can cause a multitude of problems, give an example. | A mutation in the genes which contribute to the ticking of the biological clock. |
| Name a specific issue with the biological system failing and explain it. | Familial advanced sleep-phase syndrome (FASPS) has been linked to an inherited defect of one of the genes. (Chicurel 2001). This syndrome causes sleep onset at around 7pm and spontaneous awakening at around 2am, causing people suffering from it struggling to lead a normal life |
| What is another sleep disorder and what causes it? | Research suggests that the brain changes in adolescence lead to a form of delayed sleep phase syndrome which would explain why some adolescents have unusual sleeping patterns. |
| Is there a Real World Application from this research? | Knowing how the circadian clock works is extremely beneficial from a health and safety standpoint, as knowing that a desynchronised body clock reduces alertness and can lead to accidents, we may be able to prevent such accidents in the future. |
| What have new techniques enabled researchers to study? | Behaviour of cells, molecules and genes and produce an increasingly complex picture of how living organisms function. |
| What do Chronobiologists now understand? | That the endogenous rhythms are determined by a complex synchronised multioscillator system |
| What are they still trying to work out? | The distribution of these oscillators and the exogenous cues that affect them |
| What does an evolutionary approach emphasise? | The adaptive nature of an endogenously controlled circadian rhythm. |
| What is one adaptive advantage? | The circadian clock enables tight temporal scheduling of physiological and behavioural programmes (Anton et al, 2005) |
| What is a second adaptive advantage? | Biological rhythms allow an animal (or plant) to anticipate daily environmental events, such as the patterns of light and dark. |
| Who investigated this and what did they do? | Patricia DeCoursey functionally removed the SCN in 30 chipmunks. The chipmunks were returned to their natural habitat and observed alongside two other groups of chipmunks. After 80 days, significantly more of the SCN-lesioned chipmunks had been killed by weasels, presumably because they remained awake in their burrows and the weasels could hear and locate them. |
| W | Harm may come to the animals such as the chipmunks being killed by the weasels. |
| What is a second issue with animal research? | Generalisability. The systems differ from one animal to the next, therefore we cannot be sure than human's would react/behave in the same way that animals do. |
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