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Structure of the Nervous System 1

AO1 Definitions:

Nervous system - consistes of CNS and PNS

CNS - consists of the brain and the spinal cord & is responsible for complex decisions and commands 

PNS - sends information from the outside world to the CNS and sends messages to receptors from the CNS (responses)

SNS - transmits information from receptor cells in organs to theCNS and makes muscles and glands act on messages from the CNS

ANS - transits messages to and from major organs & plays major role in the fight/flight response

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Structure of the Nervous System 2

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The Endocrine system

AO1: ENDOCRINE SYSTEM - instructs glands to secrete hormones into the bloodstream which are carried towards the target organs 

GLAND - an organ in the body able to secrete hormones, master gland is known is the pituitary gland as it controls the relase of hormones from all other glands in the body 

HORMONE - chemical substances in the blood which only affect the target organ, produced in large quantities but effects are short -lived

AO2: examples of glands and subsequent hormones: 

- testes -> testosterone 

- thyroid -> thyroxine 

- adrenals -> adrenaline 

- ovaries -> oestrogen & progesterone 

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Fight or Flight

1. The sensory receptors perceive a threat

2. message is carried via the SNS to the CNS

3. CNS coordinates the release of adrenaline from the adrenal glands (adrenal medulla) 

4. the ANS now changes from is resting (parasympathetic) state, to its aroused (sympathetic) state

5. causes many bodily changes, for example an increase in heart rate, an inhibition of non-essential bodily process for examples digestion 

6. once threat has passes, the ANS returns to its resting (parasymaptheic state) state 

*it is probable that this will appear as an application  question (AO2)

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Types of neurons

A01: neurons are basic building blocks of the nervous system, they are nerve cells that process and transmit messages through electrical and chemical signals 

3 x types of nuerons: 

1. Sensory nuerons -> carry signals from the PNS to the CNS. They have SHORT axons and LONG dendrites 

2. Relay neurons -> carry signals between neurons (sensory - motor or other relay neurons). They have SHORT axons ans SHORT dendrites 

3. Motor neurons -> carry responses from the CNS to the effectors, either glands or muscles. They have LONG axons and SHORT dendrites 

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Structure of neurons

Nucleus - contains genetic information

Dendrites - carry impulses from the nighbouring neurons towards the cell body 

Axons - carry the impulses away from the cell body, down the length of the neuron 

Myelin Sheath - fatty layer covering the axon, speeds up the electrical transmission 

Nodes of Ranvier - segment the myelin sheath, cause impluse to jump, speeding up process

Terminal Buttons - end of axons, communicate with next neuron across the synapse 

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Synaptic Transmission 1

1. When neuron = resting, its charge is negative -> when it is activated by a stimulus, the inside becomes positively charged for a split second: ACTION POTENTIAL (creates electrical impulse which travels down the neuron) 

2. each neuron has a synapse in the middle, (includes the synaptic cleft (gap) presynaptic terminal & postsynaptic receptor site). Signals WITHIN neurons are transmitted ELECTRICALLY but signals BETWEEN neurons are transmitted CHEMICALLY (synaptic transmission) 

3. When an impluse reaches end of neuron, presynaptic terminal, it triggers the release of a neurotransmitter from tiny sacs called synaptic vesticles 

4. these neurotransmitters = chemicals which diffuse across the synapse. Once diffused, it is taken up by postsynaptic receptor sites (dendrites) of the next neuron. Here is it converted back into an electrical impulse + process begins again 

5. neurotransmitters are moulded to fit thir receptor site (lock & key) + they have specilist functions, e.g acetylcholine is found where a motor neuron meets a muscle, and it causes the msucle to contract 

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Synaptic Transmission 2

6. Neurotransmitters either have an EXCITATORY or an INHIBITORY effect on neighbouring neuron:

EXCITATORY - increases the + charge of postsynaptic neuron, increasing the liklihood that said neuron will fire and carry on eletrical impluse. adrenaline

INHIBITORY - makes the charge of the neuron more thus decreasing the liklihood of the neuron firing and passing on impulse. serotonin 

SUMMATION: both effects are summed together, if net effect on postsynaptic neuron is inhibitory the neuron = less likely to fire, if net effect is excitatory then neuron = more likely to fire (also becomes momentarily postively charged) 

Action potential is only triggered if sum of both signals reaches threshold 

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Localisation of Function

Holistic theory = accepted before Broca & Wernicke (+ case of Phineas Gage), all parts of brain are involved in thoughs and processing 

Localisation of Function = theory that different areas of the brain are respnsible for different functions, e.g if specific area is damaged, associated function will be affected too

(see annotated picture of brain) 

Language -> unique in the sense that it is restricted to the left side of brain (in most people) 

Broca's area (1880s)- small area in left frontal lobe responsible for speech production, damage to this area is Broca's aphasia (slow, laborious and influent language)

Wernicke's area (1880s) - area in left temporal lobe responsible for language comprehension, damage to this area is Wernicke's aphasia (nonsense words) 

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Evaluation of Localisation of function

BRAIN SCAN EVIDENCE: Peterson et al. 1988 used brain scans to show how Broca's area was active during reading task and Wernicke's area was active during listening task + Tulving et al. (1994) used scans to show how semantic and episodic memories are in different parts of the prefrontal cortex. V objective + controlled + highly scientific 

NEUROSURGICAL EVIDENCE: The practise of Lobotomy (severing connections in frontal lobe to control agressive behaviour (Walter Freeman 1950s)) and the more modern practise of lesioning the cingulate gyrus to curb severe OCD: study by Dougherty et al. (2002) -> over 50% of 44 patients had had a full/partial resposne supportiing localisation of mental illness 

CASE STUDY: Phineas Gage, though countered by negatives about case studies (genralisibilty)

LASHLEY 1950: Higher cognitive processes e.g learning are distributed in brain in more holistic way. Investigated on rats, removing parts of cortex and found all areas were equally important in influencing the rats' ability to learn maze, meaning more complex processes = holistic. Though he expermiented on rats...

PLASTICITY: brain can compensate for lost/damaged areas after trauma or strokes, if it were completely localised, would the brain be able to do this?

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A01: also referrred to as neuroplasticity and cortical remapping, brains tendancy to adapt (functionally and physically) as a result of new experience and learning.

During infancy, number of connections in the brain peaks at arouund 15,000 (Gopnick et el. 1999) but connections not used frequently are deleted + frequently used ones are strengthened - synaptic pruning, not exclusive to childhood, happens all throughout adult life

Eleanor Maguire et el. 2000: researched London taxi drivers, and found they had more volume of hippocampus than the control group. This area is associated with spatial and navigational skills, meaning their job had actually altered the structure of their brains. The longer they had been in the job, the more pronounced the difference in volume (positive correlation)

Draganski et al 2006: imaged brains of medical students before their final exams, learning-indcued changes were seen in the posterior hippocampus and the parietal cortex as a result of the exam.

Mechelli et al. 2004: larger parietal cortexex in billingual people compared to monolingial people

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Functional recovery of the brain

A01: Following trauma/strokes, areas of the brain can compensate for their lost/damaged counterparts (an example of neural plasticity)

This process can occur quickly - spontaneous recovery - and then slow down over the following weeks/months. At this point the individual may seek other

New synaptic connections are formed, secondary neural pathways are formed/unmasked to enable functioning to continue as before (Doidge 2007)


1. Axonal sprouting - new nerve endings are grown to connect with undamaged nerve cells to form new neuronal pathways 

2. Reformation of blood vessels 

3. Recruitment of homologuous areas (similar) on the opposite side of the brain, For example if Broca's area = damaged, similar area on right hemisphere may carry out speech production

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Evaluation of Plasticity + Functional recovery 1

PRACTICAL APPLICATION: has made huge contibution to the field of nuerorehabilitation, after spontaneous recovery, physical therapy is needed to aid recovery e.g movement/electrical stimulation. Shows that brain can only fix itself to a certain extent + needs help

NEGATIVE PLASTICITY: can have maladaptive behavioural consequnces; prolonged drug use can cause a poorer level of cognitive functioning + an increased risk of demetia (Medina et al. 2007). 60 - 80% of amputees have phantom limb syndrome, continued experience of sensations in missing limb. Can be unpleasant and often painful, due to cortical reorganisation in somatosensory cortex as a result of the limb loss (Ramachandran and Hirstein 1998

AGE AND PLASTICITY: plasticity tends to reduce with age, however: Ladina Bezzola et al. 2012 used fMRI scans to investigate neural representation of movement in golfers aged 40-60 (40 hours of training), they observed reduced motor cortex activity in novice golfers compared to control group, suggesting more efficient neural reprresentations after training. Shows plasticity continues

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Evaluation of Plasticity + Functional recovery 2

ANIMAL STUDIES: David Hubel & Torsten Wiesel 1963: sewed one eye shut on a kitten + observed how the visual cortex associated with shut eye processed info from other eye, it was not idle. Ethics? is is justifiable to cause permenant damage to the animals??

COGNITIVE RESERVE: evidence from studies by Eric Schneider et al. 2014 the more time patients had spent in full-time education, the more likely they were to fully recover from their injuries. of all people he studied, patients who had 16 years of education made up 2/5 whilst those with less than 12 years made up only 12%. Confounding variable? surely not all of studied patients studied had the exact same injury meaning that the seriousness of their injury would have played a more important role in determining their recovery. Education = may merely be a correlation

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Hemispheric lateralisation and Split Brain researc

A01: the idea that both hemispheres of the brain are functionally different and that certain mental processes happen predominantly in one hemisphere, for example language (found in the left hemisphere for most people)

In order to investigate this, Rodger Sperry et el. 1968 conducted Split Brain research:

- he had 11 participants, all of which had undergone a commissurotomy, in which the corpus callosum (tissue between two hemispheres) had been cut, leaving the two hemispheres separated (to contol their epilepsy) 

- PROCEDURE: (see picture) Sperry's set up allowed for an image to be projected onto the patient's right visual field (RVF) which would be processed by the left hemisphere (LH) whilst the same/different image would be projected onto the patient's left visual field (LVF), processed by the right hemisphere (RH)

- Due to their operation, info could not be passed from one hemisphere to the other allowing Sperry to investigate the extent of lateralisation

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Hemispheric lateralisation and Split Brain researc

- FINDINGS: describe what you see -> if picture of object = shown to RVF (LH), could describe what they saw (language = in LH), if picture shown to LVF (RH) patient could not describe what they saw. NB: all of Sperry's patients had language in LH. meaning language  lateralised 

recognition by touch -> even though they could not attach verbal labels to word projected in the LVF (RH), they could select said object, e.g if word = key they could select the key from a group of objects. Shows that they understood the meaning of the word but it was the lack of a language centre in the RH, supporting lateralisation

composite words -> if two words = presented simultaneously KEY-RING, patient could pick up a key (Key = LVF - RH - left hand) and say the word ring (RVF - LH - language centre) 

matching faces -> right hemisphere = dominant in recognition, when asked to match a face from a series of faces, the RH (LVF) was consistently correct whilst the LH (RVF) was incorrect. When faced with a composite face (2 x halves), the LH was better at verbally describing the face whilst the RH was better at matching the other half of the face 

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Evaluation of Hemispheric lateralisation and Split

DEMONSTRATED FUNCTIONS: Sperry's work (and later Gazzainga's work), has produced a sizeable amount of research, main conclusion = LH is better at analytical + verbal skills (ANALYSER) whilst RH is better at spatial and musical tasks (SYNTHESISER). key contribution to our understanding to neural processes (highly influential) 

STRENGTHS OF METHODOLOGY: experiments used highly standerdised procedures, for example to ensure that the participant did not have time to move their eye, the image was projected for one tenth of a second meaning only intended visual field was used and thus only one side of the brain was used. highly controlled and objective method (high internal validity)

THEORETICAL BASIS: many debates have broken out after Sperry's work; some theorists argue the two hemispheres are so different that there is a form of duality in the brain, we all have two minds, other researchers argue that they form a highly intergrated system + are both involved in most everyday tasks. Shows that his work is valued and it is influential and valuable enough to cause debate in the science world 

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evaluation of Hemispheric lateralisation and Split

GENERALISATION: Sperry's experiment was conducted with 11 severely epileptic patients (who all had different amounts of separation following their commissotomies). Most worringly, the control group was a normal group of people, meaning there were two IVs compared to general population, (fact that they were epileptic and that they had had the operation), CONFOUNDING VARIABLE control group should have been epileptic patients with no surgery. conclusions from the experiments cannot therefore be drawn with confidence

OVERSTATED DIFFERENCE IN FUNCTION: modern neuroscientists may say that the distinciton between the two hemispheres is much more complex, and they are intergrated on a daily basis, futhermore plasticity in the brain means that one function performed by a specific hemisphere can be performed by the other when the situation requires it 

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Functional magnetic resonance imaging (fMRI)

HOW DOES IT WORK - detects changes in blood oxygenantion and flow as a result of neural activity (requires more oxygen as activity increases), HAEMODYNAMIC RESPONSE. produces a 3D image showing the active parts of the brain + the mental processes they are involved in, helps to understand localisatiom  

STRENGTHS - does not use radiation, meaning it is risk-free and non-invasive. Images have high spatial resolution, detail = depicted by the milimetre providing a v. clear picture of how brain works 

WEAKNESSES - fMRI is v. expensive + person is required to stay completely still for it to work. Has poor temporal resolution 5 second time lag behind the image on the screen and the firing of the neurons, it can only measure blood flow, cannot hone in on individual neurons meaning the type of activity shown is unclear

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Electroencephalogram (EEG)

HOW DOES IT WORK - measures electrical activity within the brain, using electrodes attached to the skull via a skull cap, records brainwaves from the millions of neurons in the brain, providing an overall picture of the activity in the brain. Often used as a diagnostic tool, as unusual patterns of activity could be the result of tumours or other disorders

STRENGTHS - invaluable in the diagnosis of epilepsy which involves bursts of activity, easily detectable on the screen, v. useful in aiding our understanding of the stages of sleep. high temporal resolution, detects activity at resoltion of a millisecond! 

WEAKNESSES - generalised nature of results, difficult to pinpoint exact source of neural activity 

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Event-related potentials (ERPs)

HOW DOES IT WORK - a teased out version of an EEG, leaving only the desired reponses for the scientists. This is done using a statisical averaging technique to block out all of the extraneous activity; leaving the event-related potentials (brainwaves triggered by specific events)

STRENGTHS - much more specificity than could be achieved through using an EEG, excellent temporal resolution (especially when compared to fMRIs). many types of ERP have emerged to describe the precise role of cognitive functioning e.g P300 component = involved in maintenence of working memory

WEAKNESSES - lack of standerdisation makes it difficult to confirm findings, and in order to obtain pure ERP data, all background noise and extraneous material has to be extracted and this is difficult to achieve

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Post-mortem examinations

HOW DOES IT WORK - analysis of a person's brain following death, these people have usually experienced a rare disorder or have displaye unusual behaviour during their lifetime. Their brain can also be compared to a neurotypical brain in order to determine the root of their behaviour/disorder 

STRENGTHS - vital in providing a foundation for both Broca's and Wernicke's areas before neuroimaging (they were both pioneers for establishing links between language and the brain) . They improve medical knowledge and help generate hypotheses for further studies 

WEAKNESSES - causation, does the injury relate to the disorder the person had, or is it a result of unrelated trauma or decay? ethical issues of informed consent, if the person in a fit state to declare that they consent to their brain being used for medical research . For example, the brain of HM (who could not form memories) was not in a position to provide consent but his brain was investigated anyway, does the knowledge outweigh the ethics?

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Circadian Rhythms

A01: biological rhythms subject to a 24 hour cycle, which regulates a number of the body's key processes for example body temp and the sleep/wake cycle

SLEEP WAKE CYCLE: we automatically feel awake during the day and drowsy at night (light as an exogenous zeigeber), would we still maintain this regular pattern of sleep and wake without daylight?...

Siffre's cave study (1962): he is a caveman who spent prolonhed periods of time underground to study the human body without natural light and sound. He resurfaced in spetember 1962 (after two months) believing it to be mid-august. In this case his body adopted a 25 hour sleep/wake cycle so he had regular periods of awake and rest despite his biological clock being free-running

Aschoff & Wever (1976): a group of p'pants spent 4 weeks in a WW2 bunker and at but one (29 hours!!) adopted a sleep/wake cycle between 24 and 25 hours. When taken in conjunction with Siffre's study, suggests that the natural sleep/wake cycle is slightly longer than 24 hours

BUT Folkard et al. (1985): studies 12 p'pants in a dark cave for 3 weeks. went to bed when clock said 11:45 and woke up when clock said 7:45. The reserachers gradually sped up clocks to by the end it was 22 hours. Majority of p'pants had difficulty adjusting, throwing into question the effect of the environment + suggesting we have strong free-runninng circadian clock

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Evaluation of circadian rhythms

PRACTICAL APPLICATION: has helped researchers to understand the consequences of shift work, where a desynchronisation from the usual rhythm occurs. Night shift workers often experience a lapse in concentration at around 6 am: circadian trough (accidents = more likely) Boivin et al. (1996) Further research by Knutsson et al. (2003) suggests that shift workers are 3x more likely to develop heart disease due to the stress of adjusting to a new sleep/wake cycle. This research helps manage economic and worker producctivity

PRACTICAL APPLICATION 2: the investigation into the bodily processes over the 24 hour period has led to the dicovery of peak absorbtion times in the day, meaning that medics canadvise patients when to take the drugs to ensure that they are the most effective, for example anticancer and anti-epileptic drugs (Balarado 2008)

USE OF CASE STUDIES: the studies which have investigated the sleep/wake cycle have typically used small groups of p'pants, meaning that they have low generalisability. Furthermore, in his most recent cave escapade in 1999, Siffre was 60 when he conducted the cave study meaning that his clock could have been even slower than the average meaning the conclusions drawn may be even less generalisible 

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Evaluation of circadian rhythms 2

INDIVIDUAL DIFFERENCES: as mentioned with Siffre, but these difference could be even more profound. Jeanne Duffy et al. (2001) revealed that some people have a natural prefence to wake + go to bed earlier than others + vice versa (larks & owls). Furthermore, it has been suggested that teenagers do not function as well in the morning (pilot study run by Dr. Paul Kelley). Could the sleep cycle be even more dependent on these individual differences?

POOR CONTROL IN STUDIES: p'pants in bunker and cave studies were deprived of natural light, but not artificial light, could still turn on lamps etc. Could artificial light be as influential on our biological clocks as natural light: Czeisler et al. (1999) concluded that it was as effective as he was able to change p'pants' cycles from 22-28 hours using artifical lighting. 

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Infradian Rhythms

A01: type of biological rhythm which has a freuency of less than 24 hours, such as menstruation or seasonal affective disorder

MENSTRUATION: governed by monthly changes in hormones, taking 28 days to complete. Oestrogen cause ovary to release an egg, during ovulation progesterone maintains uterus lining, if pregnancy does not occur then lining = shed. endogenous, but partly exogenous

Stern & McClintok (1998): took 29 women with irregular periods. Phermones taken from 9 women at different stages of cycle (cotton pad on armpit). These = frozen and then administered to other women in order of cycle. 68% of the women's cycles changed to make them more similar to their odour donor. 

SEASONAL AFFECTIVE DISORDER: circannual rhythm (occurs once a year) mental disorder, type of depression (DSM-5). Occurs in winter with low moods + lack of interest in activity, where daylight hours are the shortest. Also could be a circadian rhythm due to disruption to sleep/wake cycle caused by lack of daylight. Caused by melatonin which is released until dawn (light), during winter this process continues for longer, could reduce amount of serotonin released which is linked to onset of depression.

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Evaluation of infradian rhythms

EVOLUTIONARY BASIS OF MENSTRUATION: menstrual synchrony is beneficial for wmen as if they ovulate + have children together then they can protect their children together. Though this has been questioned by Schank (2004) who argued that if there were too many ovulating females in one group, there would be more competition from best males, thus lowering the chances for potential offspring, meaning the avoidance of menstrual synchrony would be best 

METHODOLOGICAL LIMITATIONS: synchrony studies do not factor in the other factors that can influence a woman's cycle, for example stress (confounding variables). Meaning any synchronisation could've occured by chance + these studies use a self-report scheme. Trevathan et el. (1993) did not have any results of synchrony in his sample

ANIMAL STUDIES: many of the studies into phermones = derived from animal studies, however the effect on humans is inconclusive. Can we transfer findings from animal studies onto humans??

PRACTICAL APPLICATION OF SAD: effective treatments for SAD = phototherapy which stimulates morning light to reset melatonin levels, releives symptoms in 60% of sufferers, however when a placebo was used, 30% of sufferers improved. Does this mean it is more mental and has no biological basis?

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Ultradian rhythms

A01: a type of biological rhythm with a frequency of more than one cycle in 24 hours, for example stages of sleep

There are 5 stages of sleep which span a 90 minute cycle (repeats throughout the night). Stages are identified through specific brainwaves using an EEG: 

STAGE 1& 2: Light sleep, person can easily be woken. Brainwave patterns become slower and more rhythmic (alpha waves), becoming slower as sleep becomes deeper (theta waves)

STAGE 3 & 4: involve delta waves, slower than previous stages and have greater amplitude,  this is deep sleep, it is difficult to wake someone at this point 

STAGE 5: REM sleep body = paralysed, yet brain activity increases to resemble an awake brain. Eyes are jerky, this is where is it widely believed that dreaming occurs.

SUPPORTING EVIDENCE: Dement and Kleitman (1957): monitored sleep patterns of 9 p'pants, brainwaves recorded on EEG. REM sleep was correlated with dreaming, showing the importance of REM sleep in the ultradian rhythm

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Endogenous Pacemakers

A01: Internal body clocks which regulate many biological rhythms, such as influence of the suprachiasmatic nucleus (SCN) on the sleep/wake cycle.

SCN: tiny bundle of nerves located in the hypothalamus in each hemisphere, it is one of the primary endogenous pacemakers and it maintains circadian rhythms e.g sleep cycle. Nerve fibres in the eye connect through the optic chasm to the visual area of the cerebral cortex, where the SCN lies. It receives information about light even when eye = closed (explains why we wake up when it is light)

ANIMAL STUDIES: DeCoursey et al. (2000): destroyed SCN in 30 chipmunks who were then returned to habitats. Many of them had been killed after 80 days (because they were awake when they should've been asleep). Ralph et al. (1990) bred mutant hamsters with 20 hour sleep cycle, the SCNs from these hamsters were transferred to normal hamsters and their cycles also went to 20 hours showing importance of the SCN.

Pineal gland and melatonin: SCN passes on day length and night, receives to pineal gland which induces production of melotonin (induces sleep and is inhibited during periods of wakefulness)

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Evaluation of endogenous pacemakers

BEYOND THE MASTER CLOCK: the SCN is important, but there are other rhythms (peripheral oscillators) found in lungs and liver, these are able to act independantly of the SCN, for example in study by Damiola et al. (2000) who changed feeding patterns in mice altered circadian cells in liver but left SCN unaffected. There may be other endogenous pacemakers than the SCN.

ETHICS: can we generalise findings of animal studies to humans? The animals = exposed to considerable harm and many died as a result, does what we learn from these studies justify the harm done to the animal

INTERACTIONIST SYSTEM: only in exceptional circumstances are endogenous pacemakers free-running and unaffected by exogenous zeitgebers. Isolation studies such as Siffre are extremely rare and lack validity because in real life pacemakers and zeitgebers interact.

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Exogenous Zeitgebers

A01: external cues that may affect or entertain biological rhythms such as the influence of light on the sleep/wake cycle 

LIGHT: key zeitgeber, has the ability to reset the main endogenous pacemaker (SCN), also influences hormones and blood circulation. 

Campbell & Murphy (1998): demonstrated how light could be detected by skin receptor cells, even if not received by eyes. 15 p'pants = woken various times and light was shone on the back of their knees, sleep cycles = disrupted by 3 hours in some cases. Shows how powerful light is and it doesn't even need the eyes

SOCIAL CUES: Infants' cycles fall into place with that of their families simply through social cues, e.g meal times and bedtimes imposd by adults (happens at around 16 weeks). Furthermore according to research, the best way to overcome jet lag is to adapt to the meals + bedtimes of the place you are in (their social cues).

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Evaluation of exogenous zeitgebers

OVERSTATED INFLUENCE: Miles et al. (1977): young, blind man who had a circadium rhythm of 24.9 hours and despite light + social cues, it could not be adjusted meaning he had to take sedetives at night to sleep and stimulants in the morning. Also, individuals in Artic show normal patterns despite constant exposure to light during summer. Both examples show there are instances where exogenous zeitgebers have little influence

METHODOLOGICAL ISSUES: Campbell and Murphy study has not been replicated (reliability). It has been suggested that there was some light exposure to the p'pants' eyes - a major confounding variable. Did also not condier other possible exogenous zeitgebers that could've come into effect.

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