The Role of Exogenous Zeitgebers and Endogenous Pacemakers Consequences of Disruption of Biological Rhythms

Links to the Specification The role of endogenous pacemakers and exogenous zeitgbers in the control of circadian rhythms. Disruption of biological rhythm e.g. shift work and jet lag. The role of endogenous pacemakers and exogenous zeitgbers in the control of circadian rhythms. Disruption of biological rhythm e.g. shift work and jet lag.

Past Exam Questions Jan 2011 – Discuss the role of endogenous pacemakers in the control of one or more biological rhythms (8+16 marks) June 2011 – Consider the consequences of disrupting biological rhythms (16 marks) June 2013 – Discuss research into the disruption of biological rhythms (e.g. shift work, jet lag) Jan 2011 – Discuss the role of endogenous pacemakers in the control of one or more biological rhythms (8+16 marks) June 2011 – Consider the consequences of disrupting biological rhythms (16 marks) June 2013 – Discuss research into the disruption of biological rhythms (e.g. shift work, jet lag)

Organisation By the end of this topic you should be able to: Describe and evaluate the nature of endogenous pacemakers and exogenous zeitgebers and comment on their significance to humans with reference to research evidence. Describe and evaluate research relating to the disruption of biological rhythms (shift work and jet lag) By the end of this topic you should be able to: Describe and evaluate the nature of endogenous pacemakers and exogenous zeitgebers and comment on their significance to humans with reference to research evidence. Describe and evaluate research relating to the disruption of biological rhythms (shift work and jet lag)

Independent Work/Reaching for the A* Grade Complete all lecture notes and task sheets to a high standard. Complete A3 mind maps on Endogenous Pacemakers and Exogenous Zeitgebers. Complete reading – ‘The role of the SCN’ and ‘Control of Biological Rhythms: Exogenous Zeitgebers’. Complete Consolidated Widgets task. Complete summary questions. Complete self-assessment essay tasks. AQA core text - read and take notes pp in preparation for test. Complete all lecture notes and task sheets to a high standard. Complete A3 mind maps on Endogenous Pacemakers and Exogenous Zeitgebers. Complete reading – ‘The role of the SCN’ and ‘Control of Biological Rhythms: Exogenous Zeitgebers’. Complete Consolidated Widgets task. Complete summary questions. Complete self-assessment essay tasks. AQA core text - read and take notes pp in preparation for test.

Key Terms Endogenous Pacemakers SADNocturnal DiurnalSCNPineal Gland HypothalamusMelatoninSerotonin PheromonesJet LagShift Work Exogenous Zeitgebers Delayed Sleep Phase Sleep Deprivation

Endogenous Pacemakers

What are Endogenous Pacemakers? Internal body “clocks” that regulate biological rhythms. The most important pacemakers in animals including humans are the suprachiasmatic nucleus and the pineal gland. It is likely that the activity of these pacemakers is innate. One means for testing them is to study what happens to circadian rhythms in the absence of external environmental cues. Internal body “clocks” that regulate biological rhythms. The most important pacemakers in animals including humans are the suprachiasmatic nucleus and the pineal gland. It is likely that the activity of these pacemakers is innate. One means for testing them is to study what happens to circadian rhythms in the absence of external environmental cues.

The Role of the Suprachiasmatic Nucleus A group of neurons in the hypothalamus Act as an internal clock. SCN is our most important endogenous pacemaker and controls the pineal gland and release of melatonin. A group of neurons in the hypothalamus Act as an internal clock. SCN is our most important endogenous pacemaker and controls the pineal gland and release of melatonin.

The Role of the Pineal Gland The SCN sends signals to the Pineal Gland directing it to increase the production of the hormone melatonin at night. The structure contains receptors that response to external light. Melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness. The pineal gland in birds is located beneath a thin layer of skin at the top of the brain. The SCN sends signals to the Pineal Gland directing it to increase the production of the hormone melatonin at night. The structure contains receptors that response to external light. Melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness. The pineal gland in birds is located beneath a thin layer of skin at the top of the brain.

Human Physiology of Circadian Rhythms The quality and amount of light is picked up in the retina of the eye (rods and cones) and transmitted along the optic nerve into the brain. One of the branches of the optic nerve goes to the SCN The pineal gland is triggered into action by the SCN. It produces melatonin as light decreases Melatonin influences production of serotonin. Serotonin accumulates in the raphe nuclei in the hind brain, near the pons. This stimulates the shutting down of the reticular activating system (RAS), which is associated with brain activity. We fall asleep.

Recticular Activating System (RAS)

Research Blinkley Morgan Abraham Campbell and Murphy Blinkley Morgan Abraham Campbell and Murphy

Blinkley (1972) Studied chickens Pair of pineal glands lie under the surface of a thin layer of skull at the top of the head. The gland responds to the amount of light it receives. Decrease in light – increase in hormone melatonin. This explains the regularity of the cock-crow because melatonin has decreased in response to light at dawn. Studied chickens Pair of pineal glands lie under the surface of a thin layer of skull at the top of the head. The gland responds to the amount of light it receives. Decrease in light – increase in hormone melatonin. This explains the regularity of the cock-crow because melatonin has decreased in response to light at dawn.

Morgan (1995) Hamsters have an SCN in their forebrain. When removed, their nocturnal pattern ceased. When new fetal SCN cells were implanted, they regained their circadian rhythm. When fetal SCN cells of diurnal animals placed in nocturnal animals, the nocturnal animals became diurnal. The reverse is also true. Hamsters have an SCN in their forebrain. When removed, their nocturnal pattern ceased. When new fetal SCN cells were implanted, they regained their circadian rhythm. When fetal SCN cells of diurnal animals placed in nocturnal animals, the nocturnal animals became diurnal. The reverse is also true.

Other Research Campbell and Murphy (1998) Applied light to the back of the knees of human participants and were able to shift the circadian rhythm in body temperature and body secretion. Abraham (2000) Injections of melatonin can induce sleep in sparrows. Campbell and Murphy (1998) Applied light to the back of the knees of human participants and were able to shift the circadian rhythm in body temperature and body secretion. Abraham (2000) Injections of melatonin can induce sleep in sparrows.

Evaluation - Methodology Sample Data type Individual Differences Cause and Effect Extraneous Variables Ecological Validity Consistency of findings? Sample Data type Individual Differences Cause and Effect Extraneous Variables Ecological Validity Consistency of findings?

Evaluation - IDA Is Psychology a Science? Biological Approach Reductionism Determinism Ethical Issues Real World Application? Is Psychology a Science? Biological Approach Reductionism Determinism Ethical Issues Real World Application?

Exogenous Zeitgebers

What are exogenous zeitgebers? Exogenous = Outside the organism Zeitgeber = German for time giver. An environmental factor that can act as a time cue e.g. light, noise, clocks etc. Light is necessary to reset the internal body clock everyday so that the biological rhythm is co- ordinated with the outside world. Exogenous = Outside the organism Zeitgeber = German for time giver. An environmental factor that can act as a time cue e.g. light, noise, clocks etc. Light is necessary to reset the internal body clock everyday so that the biological rhythm is co- ordinated with the outside world.

Research Light – Campbell and Murphy Biochemical – McClintock Social Cues - Davidson Light – Campbell and Murphy Biochemical – McClintock Social Cues - Davidson

Campbell and Murphy Applied light to the back of the knees of human participants and were able to shift the circadian rhythm in body temperature and melatonin production. This shows that light can reach the brain without passing through the eyes. Applied light to the back of the knees of human participants and were able to shift the circadian rhythm in body temperature and melatonin production. This shows that light can reach the brain without passing through the eyes.

McClintock Found a “dormitory effect” of synchronisation of menstrual cycles in a women’s dormitory. It appears pheromones from other women acts as zeitgeber. Women who work with men tend to have shorter menstrual cycles. Found a “dormitory effect” of synchronisation of menstrual cycles in a women’s dormitory. It appears pheromones from other women acts as zeitgeber. Women who work with men tend to have shorter menstrual cycles.

Davidson Until recently it was thought that social cues were the main Ezs – we eat, go to bed, get up etc at socially determined times. It seemed our bodily rhythms were entrained by social convention, not internal biology. Today we know that light is the dominant EZ, however all parts of the body have their own rhythm and not all of them are reset by light. E.g. zeitgebers for heart and liver appear to be reset by eating. Until recently it was thought that social cues were the main Ezs – we eat, go to bed, get up etc at socially determined times. It seemed our bodily rhythms were entrained by social convention, not internal biology. Today we know that light is the dominant EZ, however all parts of the body have their own rhythm and not all of them are reset by light. E.g. zeitgebers for heart and liver appear to be reset by eating.

Evaluation - Methodology Sample Data type Individual Differences Cause and Effect Extraneous Variables Ecological Validity Consistency of findings? Sample Data type Individual Differences Cause and Effect Extraneous Variables Ecological Validity Consistency of findings?

Evaluation - IDA Is Psychology a Science? Biological Approach Reductionism Determinism Ethical Issues Real World Application? Is Psychology a Science? Biological Approach Reductionism Determinism Ethical Issues Real World Application?

Disrupting Biological Rhythms

We use stimuli around us to co-ordinate biological clocks. Lengthening and shortening of the day is reflected in sleep/wake cycles. Inuit Eskimos have regular sleep/wake cycle even though continuous daylight in summer and darkness in winter (social cues dominant zeitgeber). If exogenous cues change rapidly the co- ordination between external and internal rhythms breaks down. We use stimuli around us to co-ordinate biological clocks. Lengthening and shortening of the day is reflected in sleep/wake cycles. Inuit Eskimos have regular sleep/wake cycle even though continuous daylight in summer and darkness in winter (social cues dominant zeitgeber). If exogenous cues change rapidly the co- ordination between external and internal rhythms breaks down.

Shift Work

Shift Work/Lag Night workers are required to be alert at night and so must sleep during the day which is the reverse of our natural rhythms and out of line with most of the available cues from zeitgebers.

Disasters The Exxon Valdez oil tanker ran aground at 12.04am in 1989 dumping more than 10 million gallons of oil into Prince William Sound, Alaska, killing thousands of marine animals. Chernobyl nuclear power station disaster began at 4.00am. The Exxon Valdez oil tanker ran aground at 12.04am in 1989 dumping more than 10 million gallons of oil into Prince William Sound, Alaska, killing thousands of marine animals. Chernobyl nuclear power station disaster began at 4.00am.

Disasters Most lorry accidents occur between 4 – 7am. US - $77 billion annually as a result of both major accidents and ongoing medical expenses due to shift work related illnesses. Most lorry accidents occur between 4 – 7am. US - $77 billion annually as a result of both major accidents and ongoing medical expenses due to shift work related illnesses.

Research Czeisler (1982) Sharkey (2001) Czeisler (1982) Sharkey (2001)

Czeisler (1982) Study of a chemical plant in Utah. High incidence of health problems, sleep difficulties and work-related stress in staff on short-rotation shifts. Recommended change to 21 day shift cycle (instead of 7) and to phase delay. After 9 months worker satisfaction was significantly increased and factory output higher. Study of a chemical plant in Utah. High incidence of health problems, sleep difficulties and work-related stress in staff on short-rotation shifts. Recommended change to 21 day shift cycle (instead of 7) and to phase delay. After 9 months worker satisfaction was significantly increased and factory output higher.

Sharkey (2001) Investigated use of melatonin. 2 simulated shift patterns in a laboratory, 6 days at a time. Found melatonin could speed up biological adjustment to shift patterns and increased sleep time during non-work periods. Investigated use of melatonin. 2 simulated shift patterns in a laboratory, 6 days at a time. Found melatonin could speed up biological adjustment to shift patterns and increased sleep time during non-work periods.

Evaluation - Methodology Sample Data type Individual Differences Cause and Effect Extraneous Variables Ecological Validity Consistency of findings? Sample Data type Individual Differences Cause and Effect Extraneous Variables Ecological Validity Consistency of findings?

Evaluation - IDA Is Psychology a Science? Biological Approach Reductionism Determinism Ethical Issues Real World Application – business, avoiding disasters? Is Psychology a Science? Biological Approach Reductionism Determinism Ethical Issues Real World Application – business, avoiding disasters?

Jet Lag

What is it? Refers to the physiological effects of disrupted circadian rhythms. Symptoms – loss of appetite, nausea, fatigue, disorientation, insomnia and mild depression The dorsal portion of the SCN takes several cycles to fully resynchronise to abrupt changes in environmental time. Winter et al (2008) – one day per hour of time change. Refers to the physiological effects of disrupted circadian rhythms. Symptoms – loss of appetite, nausea, fatigue, disorientation, insomnia and mild depression The dorsal portion of the SCN takes several cycles to fully resynchronise to abrupt changes in environmental time. Winter et al (2008) – one day per hour of time change.

Phase Advance and Phase Delay Most travellers have less difficulty in adjusting when flying west (e.g. London to New York, Phase Delay) than when flying east (e.g. New York to London, Phase Advance) Easier to stay up later than normal rather than getting up earlier. Phase delay – you get up when your body is already awake. Most travellers have less difficulty in adjusting when flying west (e.g. London to New York, Phase Delay) than when flying east (e.g. New York to London, Phase Advance) Easier to stay up later than normal rather than getting up earlier. Phase delay – you get up when your body is already awake.

Phase Advance and Phase Delay

Research Recht et al (1995) Takahashi et al (2002) Recht et al (1995) Takahashi et al (2002)

Recht et al (1995) Analysed US baseball results over 3 year period. Teams that travelled east to west won on average 44% of games. Teams that travelled west to east won on average 37%. Analysed US baseball results over 3 year period. Teams that travelled east to west won on average 44% of games. Teams that travelled west to east won on average 37%.

Takahasi et al (2002) Researched use of melatonin. 8 participants, blood samples before and after 11 hour eastward flight. Melatonin speeded up the resynchronisation of biological rhythms and reduced symptoms of jet lag. Researched use of melatonin. 8 participants, blood samples before and after 11 hour eastward flight. Melatonin speeded up the resynchronisation of biological rhythms and reduced symptoms of jet lag.

Evaluation - Methodology Sample Data type Individual Differences Cause and Effect Extraneous Variables Ecological Validity Consistency of findings? Sample Data type Individual Differences Cause and Effect Extraneous Variables Ecological Validity Consistency of findings?

Evaluation - IDA Is Psychology a Science? Biological Approach Reductionism Determinism Ethical Issues Real World Application – business, avoiding disasters? Is Psychology a Science? Biological Approach Reductionism Determinism Ethical Issues Real World Application – business, avoiding disasters?

Progress Check Quick Questions: 1.Where is the SCN? 2.Describe a piece of research that highlights the importance of the SCN? 3.Give one example of an EZ. 4.Give a piece of research to support that EZ. Quick Questions: 1.Where is the SCN? 2.Describe a piece of research that highlights the importance of the SCN? 3.Give one example of an EZ. 4.Give a piece of research to support that EZ.

Progress Check Stretch and Challenge Question: To what extent can PMS be used to excuse women from criminal responsibility? Stretch and Challenge Question: To what extent can PMS be used to excuse women from criminal responsibility?