Aqa A-level Psychology Pya4: Endogenous Pacemakers And Exogenous Zeitgebers
This document was uploaded by user and they confirmed that they have the permission to share it. If you are author or own the copyright of this book, please report to us by using this DMCA report form. Report DMCA
Overview
Download & View Aqa A-level Psychology Pya4: Endogenous Pacemakers And Exogenous Zeitgebers as PDF for free.
More details
- Words: 1,285
- Pages: 16
The Role of Endogenous Pacemakers and Exogenous Zeitgebers …
What are they? •
Most organisms have an internal biological ‘clock’ which controls the circadian rhythm (24hr cycle) • You biological clock is endogenous (part of the internal organism) • Biological clock helps us to realise an event (i.e. the coming of night) Because your clock effectively instructs neural structures (paces them) over a 24hr cycle this is known as an Endogenous Pacemaker •
•
Seasons = clock to be re-set. To achieve this your clock is re-set each day using cues in the environment (cues are outside the body referred to as exogenous.) These exogenous cues (light, etc.) are known as zeitgebers.
Endogenous Pacemakers •
Biological Clock Ticking of clock created by reactions between proteins. Darlington et al. (1998) describes… • • • •
Proteins ‘CLOCK’ & ‘CYCLE’ bind together in the morning… This causes the increase in the production of proteins ‘PER’ & ‘TIM’, during the day… As these increase, production of CLOCK-CYCLE decrease… As they decrease production of PER-TIM fall and CLOCK-CYCLE increase … ready to begin cycle again … (new day)
Endogenous Pacemakers • Suprachiasmatic Nucleus (SCN) Main endogenous pacemaker found in the hypothalamus. SCN is a pair of tiny clusters of nerve cells. One half in left hemisphere of the brain and one on the right. Just above where the optic nerve from each eye cross over (optic chiasm). SCN obtains info. on light from the optic nerve even when shut. Special photoreceptors in the eyes pick up light signals and carry them to SCN. If our endogenous clock is running slow (i.e. sun rises earlier than day before), the morning light automatically shifts the clock ahead. So rhythm is in step with the world outside
Endogenous Pacemakers •
Pineal Gland & Melatonin SCN not only endogenous pacemaker. Pineal gland contain light-sensitive cells. Light = production of melatonin in the gland is stopped. So, when levels of light fall, melatonin is produced = inducing sleep Therefore… Light, the pineal gland and melatonin regulate the sleep-wake cycle. Pineal gland is really important as a pacemaker in birds and reptiles.
AO2 • SCN If SCN is damaged/removed from a organism, sleepwake patterns are affected (i.e. DeCoursey et al. 2000) suggesting the importance of the SCN in controlling biological rhythms. Morgan, 1995 - if ‘mutant’ hamsters are bred so they have a circadian rhythm of 20 instead of 24hrs and transplanted into normal hamsters, the normal ones will display the 20hr rhythm. Showing the role of SCN as a pacemaker. SCN seems to be the main clock, but body temp. rhythm continue to exist when the SCNs are removed, suggesting another clock. Folkard, 1996 - Kate Aldcroft spent weeks in cave, after 25 days, temp. adopted a 24hr rhythm but her sleep rhythm adopted a 30hr cycle.
AO2 • Pineal Gland & Melatonin Moyer et al. 1997 - light causes pineal gland to produce melatonin in lizards. If the gland is removed, it continues to produce melatonin rhythmically in response to light for up to 10 days. Potocki et al. 2000 - levels of melatonin are inverted for those who suffer from Smith-Magenis syndrome (difficult falling asleep). Taking supplements of melatonin at night can help with symptoms = supporting role of melatonin in sleep-wake cycle. Sackett & Korner, 1993 - melatonin circulates in the blood, so would expect ‘Siamese’ twins to share circadian rhythms, but they do not; questioning the role of melatonin.
Question Time •
What is an endogenous pacemaker?
•
How does Darlington et al. (1998) describe the reaction between proteins? (process)
•
What is the SCN? Where is it? What does it do?
•
Other than the SCN, what else is an endogenous pacemaker?
•
What did Morgan, 1995 find? (hamsters)
•
Who looked into ‘Siamese’ twins?
•
Potocki et al. 2000 found?
Process of resetting the clock with exogenous zeitgebers is known as entrainment…
Exogenous Zeitgebers • Social Cues Biologists thought that social cues were the main zeitgebers (external cues) for human circadian rhythm. We eat meals at socially-determined meal times (12.00 - Lunch), we go to bed and wake up at times designated appropriate for our age, etc.. Our daily rhythms appeared to be reset (entrained) by social convention, not internal biology (SCN, pineal gland/melatonin) However its been recognised that …
Exogenous Zeitgebers • Light Light is the dominant zeitgeber in humans. After discovery that exposure to bright light suppresses melatonin production (Wever et al. 1983) Hall, 2000 - certain proteins (cryptochromes) in the body detect light … explaining that shining a light on the back of ppt. knees changed their circadian rhythms (Campbell & Murphy, 1998) Importance of light as a time-giver can be difficult in blind people. Lack of info. on light messes up their sleep patterns. One man (blind) had a circadian rhythm of 24.9hrs. Exposed to various exogenous zeitgebers (social cues, etc.) yet found great difficulty reducing his internal pace, showing light is the most important zeitgeber. (Miles et al. 1977)
Exogenous Zeitgebers •
Temperature Biological rhythms can be also entrained by temperature. E.g. leaves on a deciduous trees change colour and fall because of changes in temp. Temperature is also a factor of hibernation. However… No evidence to show that temperature affects human biological rhythms
AO2 • Social Cues Social cues provide a means of controlling social behaviours (example in book, pg. 65) • Light Light cues sometimes are insufficient to override the free-running clock (free of exogenous cues). Kelly et al. 1999 – US nuclear submariners live on an 18hr day. All cues available (light, social, etc.) didn’t shift the rhythm of melatonin production onto their 18hr day, the rhythm remained tat 24hrs. On a biochemical level, its been found that light destroys the TIM portion of the PER-TIM protein, which re-sets the biological clock
AO2 • Why is Light important? Animals want to stay active when its light, safe from predators (vice versa). Animals have an internal clock that tells them when to wake up but their circadian rhythm doesn’t match day length because daylight changes over the course of the year. • What about blind people? Czeisler et al. 1995 – found some blind people do respond to bright light exposure with reduced melatonin production. Suggesting… there are 2 pathways to the brain from the eyes. 7. For conscious vision 8. For light travelling to the SCN
Question Time 1. What is meant by exogenous zeitgebers? 3. What 3 zeitgebers help reset your clock? 5. Other than the SCN, what in the body also detects changes in light? (Hall, 2000) 7. What did Miles et al. 1977 find? 9. Who live on an 18hr day and what did Kelly et al. 1999 find? 11. Who discovered that some blind people respond to bright light exposure?
AO2 •
Advantages of endogenous pacemakers & exogenous zeitgebers We need pacemakers, otherwise there would be problems. If an animals rhythm relied on environmental cues: we might sleep most of the day in winter. DeCoursey et al. 2000 - destroyed SCN in chipmunks and found they became more active ay night than normal chipmunks and more likely to be eaten by predators Exogenous zeitgebers allow animals to respond to changes in the environment, without them an animal might be awake at unsuitable times.
AO2, finally… •
Disadvantage of Biological rhythms Biological rhythms will not change when you want them to, for example when travelling across time zones. It is possible that your mind can have some influence… Born et al. 1999 – found people who were told to wake up earlier than usual had higher levels of the stress hormone adrenocortotrophic (contributes to the waking-up process) than normal at the designated time and woke up earlier
What are they? •
Most organisms have an internal biological ‘clock’ which controls the circadian rhythm (24hr cycle) • You biological clock is endogenous (part of the internal organism) • Biological clock helps us to realise an event (i.e. the coming of night) Because your clock effectively instructs neural structures (paces them) over a 24hr cycle this is known as an Endogenous Pacemaker •
•
Seasons = clock to be re-set. To achieve this your clock is re-set each day using cues in the environment (cues are outside the body referred to as exogenous.) These exogenous cues (light, etc.) are known as zeitgebers.
Endogenous Pacemakers •
Biological Clock Ticking of clock created by reactions between proteins. Darlington et al. (1998) describes… • • • •
Proteins ‘CLOCK’ & ‘CYCLE’ bind together in the morning… This causes the increase in the production of proteins ‘PER’ & ‘TIM’, during the day… As these increase, production of CLOCK-CYCLE decrease… As they decrease production of PER-TIM fall and CLOCK-CYCLE increase … ready to begin cycle again … (new day)
Endogenous Pacemakers • Suprachiasmatic Nucleus (SCN) Main endogenous pacemaker found in the hypothalamus. SCN is a pair of tiny clusters of nerve cells. One half in left hemisphere of the brain and one on the right. Just above where the optic nerve from each eye cross over (optic chiasm). SCN obtains info. on light from the optic nerve even when shut. Special photoreceptors in the eyes pick up light signals and carry them to SCN. If our endogenous clock is running slow (i.e. sun rises earlier than day before), the morning light automatically shifts the clock ahead. So rhythm is in step with the world outside
Endogenous Pacemakers •
Pineal Gland & Melatonin SCN not only endogenous pacemaker. Pineal gland contain light-sensitive cells. Light = production of melatonin in the gland is stopped. So, when levels of light fall, melatonin is produced = inducing sleep Therefore… Light, the pineal gland and melatonin regulate the sleep-wake cycle. Pineal gland is really important as a pacemaker in birds and reptiles.
AO2 • SCN If SCN is damaged/removed from a organism, sleepwake patterns are affected (i.e. DeCoursey et al. 2000) suggesting the importance of the SCN in controlling biological rhythms. Morgan, 1995 - if ‘mutant’ hamsters are bred so they have a circadian rhythm of 20 instead of 24hrs and transplanted into normal hamsters, the normal ones will display the 20hr rhythm. Showing the role of SCN as a pacemaker. SCN seems to be the main clock, but body temp. rhythm continue to exist when the SCNs are removed, suggesting another clock. Folkard, 1996 - Kate Aldcroft spent weeks in cave, after 25 days, temp. adopted a 24hr rhythm but her sleep rhythm adopted a 30hr cycle.
AO2 • Pineal Gland & Melatonin Moyer et al. 1997 - light causes pineal gland to produce melatonin in lizards. If the gland is removed, it continues to produce melatonin rhythmically in response to light for up to 10 days. Potocki et al. 2000 - levels of melatonin are inverted for those who suffer from Smith-Magenis syndrome (difficult falling asleep). Taking supplements of melatonin at night can help with symptoms = supporting role of melatonin in sleep-wake cycle. Sackett & Korner, 1993 - melatonin circulates in the blood, so would expect ‘Siamese’ twins to share circadian rhythms, but they do not; questioning the role of melatonin.
Question Time •
What is an endogenous pacemaker?
•
How does Darlington et al. (1998) describe the reaction between proteins? (process)
•
What is the SCN? Where is it? What does it do?
•
Other than the SCN, what else is an endogenous pacemaker?
•
What did Morgan, 1995 find? (hamsters)
•
Who looked into ‘Siamese’ twins?
•
Potocki et al. 2000 found?
Process of resetting the clock with exogenous zeitgebers is known as entrainment…
Exogenous Zeitgebers • Social Cues Biologists thought that social cues were the main zeitgebers (external cues) for human circadian rhythm. We eat meals at socially-determined meal times (12.00 - Lunch), we go to bed and wake up at times designated appropriate for our age, etc.. Our daily rhythms appeared to be reset (entrained) by social convention, not internal biology (SCN, pineal gland/melatonin) However its been recognised that …
Exogenous Zeitgebers • Light Light is the dominant zeitgeber in humans. After discovery that exposure to bright light suppresses melatonin production (Wever et al. 1983) Hall, 2000 - certain proteins (cryptochromes) in the body detect light … explaining that shining a light on the back of ppt. knees changed their circadian rhythms (Campbell & Murphy, 1998) Importance of light as a time-giver can be difficult in blind people. Lack of info. on light messes up their sleep patterns. One man (blind) had a circadian rhythm of 24.9hrs. Exposed to various exogenous zeitgebers (social cues, etc.) yet found great difficulty reducing his internal pace, showing light is the most important zeitgeber. (Miles et al. 1977)
Exogenous Zeitgebers •
Temperature Biological rhythms can be also entrained by temperature. E.g. leaves on a deciduous trees change colour and fall because of changes in temp. Temperature is also a factor of hibernation. However… No evidence to show that temperature affects human biological rhythms
AO2 • Social Cues Social cues provide a means of controlling social behaviours (example in book, pg. 65) • Light Light cues sometimes are insufficient to override the free-running clock (free of exogenous cues). Kelly et al. 1999 – US nuclear submariners live on an 18hr day. All cues available (light, social, etc.) didn’t shift the rhythm of melatonin production onto their 18hr day, the rhythm remained tat 24hrs. On a biochemical level, its been found that light destroys the TIM portion of the PER-TIM protein, which re-sets the biological clock
AO2 • Why is Light important? Animals want to stay active when its light, safe from predators (vice versa). Animals have an internal clock that tells them when to wake up but their circadian rhythm doesn’t match day length because daylight changes over the course of the year. • What about blind people? Czeisler et al. 1995 – found some blind people do respond to bright light exposure with reduced melatonin production. Suggesting… there are 2 pathways to the brain from the eyes. 7. For conscious vision 8. For light travelling to the SCN
Question Time 1. What is meant by exogenous zeitgebers? 3. What 3 zeitgebers help reset your clock? 5. Other than the SCN, what in the body also detects changes in light? (Hall, 2000) 7. What did Miles et al. 1977 find? 9. Who live on an 18hr day and what did Kelly et al. 1999 find? 11. Who discovered that some blind people respond to bright light exposure?
AO2 •
Advantages of endogenous pacemakers & exogenous zeitgebers We need pacemakers, otherwise there would be problems. If an animals rhythm relied on environmental cues: we might sleep most of the day in winter. DeCoursey et al. 2000 - destroyed SCN in chipmunks and found they became more active ay night than normal chipmunks and more likely to be eaten by predators Exogenous zeitgebers allow animals to respond to changes in the environment, without them an animal might be awake at unsuitable times.
AO2, finally… •
Disadvantage of Biological rhythms Biological rhythms will not change when you want them to, for example when travelling across time zones. It is possible that your mind can have some influence… Born et al. 1999 – found people who were told to wake up earlier than usual had higher levels of the stress hormone adrenocortotrophic (contributes to the waking-up process) than normal at the designated time and woke up earlier
Related Documents
More Documents from "Nader Smadi"
