Biopsych Flashcards
what are the 2 main functions of the nervous system
- to collect, process and respond to information in the environment
- to coordinate the working of different organs and cells in the body
what are the structures and functions of the central nervous system (CNS)
- the CNS is made up of the brain and the spinal cord
- the brain is the centre of all conscious awareness
- the outer layer of the brain, the cerebral cortex, is highly developed in humans and is what distinguishes our higher mental functions from those from those of animals
- the spinal cord is an extension of the brain and is responsible for reflex actions
- it passes messages to and from the brain and connections nerves to the PNS
what is the structure and function of the peripheral nervous system (PNS)
- the PNS transmits messages, via millions of neurons, to and from the nervous system
- the PNS is further sub divided into the autonomic nervous system (ANS) and the somatic nervous system (SNS)
what is the autonomic nervous system
the ANS governs vital functions in the body such as breathing, heart rate, digestion, sexual arousal and stress response
what is the somatic nervous system (SNS)
the SNS controls muscle movement and receives information from sensory receptors
the \autonomic nervous system is subdivided into the
- sympathetic nervous system
2. parasympathetic nervous system
what are the key function of the endocrine system
the endocrine system works alongside the nervous system to control vital functions in the body through the action of hormones
it works much more slowly than the nervous system but has widespread and powerful effects.
what are glands and what do they do
glands are organs in the body that produce hormones.
what is the major endocrine gland
the major endocrine gland is the pituitary gland located in the brain. it is called the master gland because it controls the release of hormones from all the other endocrine glands in the body.
what are hormones
hormones are secreted into the bloodstream and affect any cell in the body that has a specific receptor for it
thyroxine
a hormone produced by the thyroid gland affects cells in the heart and also cells throughout the body which increase metabolic rates. this in turn affects growth rates.
what does the endocrine system work in parallel with
the autonomic nervous system
what happens to the endocrine system and the ANS during a stressful event
- when a stressor is perceived, the hypothalamus triggers activity in the sympathetic branch of the ANS. the ANS changes from its normal resting state (parasympathetic) to the physiologically aroused sympathetic state
- the stress hormone adrenaline is released from the adrenal medulla in to the blood stream
- adrenaline triggers physiological changes in target organs in the body. the fight or flight response
- once the threat has passed the parasympathetic nervous system returns the body to its resting state.
what is the effect of adrenaline
increased heart rate
dilation of the pupils
decreased production of saliva
the effects of the sympathetic state
readies body for fight or flight
- increases heart rate
- increases breathing rate
- dilates pupils
- inhibits digestion
- inhibits saliva production
- stimulates urination
the effects of the parasympathetic state
rest and digest
- decreases hear rate
- decreases breathing rate
- constricts pupils
- stimulates digestion
- stimulates saliva production
where are the majority of nervous cells located
there are 100 billion nerve cells in the nervous system,
80% are located in the brain
what are the 3 types of neurons
- sensory neurons
- relay neurons
- motor neurons
what is the sensory neuron
carries messages from the PNS to the CNS.
they have short dendrites and long axons
what are relay neurons
connect sensory neurons to motor or other relay neurons.
they have short dendrites and short axons
what are the motor neurons
connects the CNS to effectors such as muscles and glands. they have short dendrites and long axons
what do all neurons contain
- cell body
- dendrites
- axon: myelin sheath and nodes of ranvier
- terminal buttons
what are dendrites
branch like structures that protrude from the cell body. these carry nerve impulses from neighbouring neurons towards the cell body
what is the axon
carries the electrical impulses away from the cell body down the length of the neurons.
myelin sheath
it covered in a fatty layer that protects the axon
nodes of ranvier
gaps in the axon speed up the transmission of the impulse
terminal buttons
at the end of the axon communicate with the next neuron in the chain across a gap called the synapse
electrical transmission
when a neuron is in a resting state the inside of the cell is negatively charged compared to the outside -70 mv
when a neuron is activated, the inside of the cell becomes positively charged for a split second causing an action potential to occur
this creates an electrical impulse that travels down the axon towards the end of the neuron.
synapse
each neuron is separated from the next by a tiny gap called the synapse
what is a neurotransmitter
are chemicals that diffuse across the synapse to the next neuron in the chain
several dozen neurotransmitter have been identified. each has its own specific molecular structure that fits perfectly into a postsynaptic receptor site.
acetylcholine (ACh)
a neurotransmitter. found where a motor neuron meets a muscle causing muscles to contract
serotonin
a neurotransmitter it affects mood and social behaviour which is why it has been implicated in OCD and depression
an inhibitory, increasing the negative charge of the postsynaptic neuron, making it less likely the neuron will fire.
adrenaline
neurotransmitter
generally excitatory, increasing the positive charge of the postsynaptic neuron, making it more likely the neuron will fire
dopamine
neurotransmitter
is an usual neurotransmitter as it is equally likely to have excitatory or inhibitory effect on the next neuron in the chain.
summation
excitatory and inhibitory influences are summed and must reach a certain threshold in order for the action postsynaptic neuron to be triggered.
if the net effect of the neurotransmitters is inhibitory then the postsynaptic neuron is less likely to fire.
it is more likely to fire if the net effect is excitatory.
synaptic transmission
when the electrical impulse reaches the end of the neuron (the presynaptic terminal) it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles.
once the neurotransmitter crosses the gap, it is take up by the postsynaptic receptor site on the next neuron.
the chemical message is converted back into an electrical impulse and the process of electrical transmission begins
lateralisation
some physical and psychological functions are controlled by a particular hemisphere.
the left side of the body is controlled by the right hemisphere vis versa
cerebral cortex
outer layer of brain is called the cerebral cortex.
it covers the inner parts of the brain. It is about 3 mm thicj and it separates us from lower animals as it is highly developed.
the cortex appears grey due to the location of the cell bodies. grey matter.
motor area
the back of the frontal lobe (of both hemispheres)
controls voluntary movement.
damage may result in loss of control over fine motor movements
somatosensory area
front of the parietal loves.
processes sensory information from the skin. the amount of somatosensory area devoted to a particular body part denotes its sensitivity
visual area
in the optical lobe at the back of the brain
each eye sends information from the right visual field to the left visual cortex vis versa
so damage to the left hemisphere, for example, can produce blindness in the right visual field of both eyes.
auditory area
in the temporal lobe
analyses speech based information.
damage may produce partial hearing loss, the more extensive the damage, the more serious the loss.
Broca’s area
identified by Broca in the 1880s
in the left frontal lobe. speech production
damage to this area causes Broca’s aphasia which is characterised by speech that is slow, laborious and lacking in fluency.
Broca’s patients may have difficulty finding words and naming certain objects
patients with Broca’s aphasia have difficulty with preposition and conjugations.
Wernicke’s area
in the frontal temporal lobe, language comprehension.
patients produce language but have problems understanding it, so they produce fluent but meaningless speech.
patients with Wernicke’s aphasia will often produce nonsense words (noelogisms) as part of the content of their speech.
evaluation of localisation and function in the brain
strengths
- brain scan evidence: Peterson et al used brain scans to show activity in wernkicks and broca. Tulving revealed semantic and episodic memories are located in different parts of the frontal cortext.
- neurological evidence: surgically removing or destroying airs of the brain. 44 OCD patients who had a cingulotomny at 32 week follow up 1/3 met successful response.
- case studies: unique cases of neurological damage such as phineas gage. personality changed frontal lobe responsible for regulating mood.
evaluation of localisation and function in the brain
weaknesses
- contradictory research: Lashley suggested higher cognitive functions are not localised. removed between 10 and 50% of the cortex in rats learning a maze. no one area was more important. as learning requires every part of the cortex.
- neural plasticity. when the brain becomes damaged and function has been compromised or lost the rest of the brain is able to reorganise itself to recover the function. Lashley called this the law of equipotentiality other parts ot he brain chip in so the same action can be achieved. several documented cases of this.
brain plasticity
synaptic connects can be formed and are pruned
during infancy, the brain experiences a rapid growth in synaptic connections, peaking at about 15,000 at age 2-3
as we age, rarely used connections are deleted and frequently used connections are strengthened, synaptic pruning.
research suggests that neural connections can change or be formed at any time, due to learning and experience
what is synaptic pruning
as we age rarely used connections are deleted and frequently used connections are strengthened
Maguire et al (2000)
brain plasticity
found significantly more volume of grey matter in the posterior hippocampus in London taxi drivers than is a matched control group. This part of the brain is linked with the development of spatial and navigational skills.
as part of their training, London cabbies take a complex test called the knowledge to assess their recall of city streets and possible routes. This learning experience appears to alter the structure of the taxi drivers’ brains.
the longer they had been in the job the more pronounced was the structural difference.
Draganski et al (2006)
brain plasticity
imaged the brains of medical students 3 months before and after final exams.
learning induced changes were seen in the posterior hippocampus and the parietal cortex, presumably as a result of the exam.
functional recovery of the brain after trauma
following trauma unaffected areas of the brain take over lost functions
functional recovery of the brain after trauma is an important example of neural plasticity. Healthy brain areas take over functions of areas damaged, destroyed or even missing.
neuro-scientists suggests this process occurs quickly after trauma (spontaneous recovery) and then slows down- at which point the person may require rehabilitative therapy.
how does functional recovery happen
the brain is able to rewire and reorganise itself by forming new synaptic connections close to the area of damage.
secondary neural pathways that would not typically be used to carry out certain functions are activated or unmasked to enable functioning to continue.
what are the 3 different structural changes in functional recovery
- axon sprouting: growth of new nerve endings which connect with other undamaged cells to form a new neuronal pathways
- reformation of blood vessels
- recruitment of homologous (similar) areas on the opposite side of the brain to perform specific tasks.
evaluation of plasticity and functional recovery
strengths
- practical application. understanding processes involved in plasticity contributed to neuro-rehabilitation. techniques include movement and electrical stimulation of the brain. at a point it the brain requires further intervention for functional recovery
- animal studies. Hubel and wiesel sewed one eye of a kitten shut and analysed the brain’s cortical responses. the area of the visual cortex associated continued to process information from the open eye. compensatory activity in the brain.
evaluation of plasticity and functional recovery
limitations
- potential -ve consequences. maladaptive behavioural consequences. prolonged drug use result in poorer cognitive functioning and increased risk of dementia. 60 - 80% of amputees develop phantom limb syndrome due to reorganisation in the somatosensory cortex. not always beneficial.
- age ad plasticity relationship complex. functional recovery reduces with age. brain has a greater propensity for reorganisation in childhood as it constantly adapts to new experiences and learning. Bezzola et al demonstrated 40 years of golf training produced changes in the neural representation of movement in older people. does continue through life time.
- cognitive reserve. person’s educational attainment may influence how well the brain adapts. found the more time brain injury patients had spent in education the greater their chances of recovery.
hemispheric lateralisation
concerns behaviour controlled by just one hemisphere
e.g language is controlled by the left hemisphere
Sperry (1968)
Background and aim
split brain research
sought to demonstrate that the 2 hemispheres were specialised for certain functions and could perform tasks independently of one another.
normally the hemispheres are connected by the corpus callosum and a few other structures.
a commissurotomy is an operation to cut the corpus callosum and is sometimes performed to control epileptic seizures.
sperry studied a group of epileptics who had the operation
Sperry
general procedure
an image or word is projected to a patients right visual field (RVF) (so is processed by the left brain) and another image to the left visual field LVF ( so is processed by the right brain). for 1/10 of a second
in the normal brain, the corpus callosum shares information between both hemispheres. in a split brain, the information cannot be conveyed from the chosen hemisphere to the other.
4 variations in Sperry’s research
- describing what was seen
- recognition by touch
- composite words
- matching faces.
Sperry
describing what was seen
object shown to
- RVF –> patient easily describes what is seen
- LVF —> patient says there was nothing there
can’t describe objects in the LVF because the RH usually lacks language centres.
messages received by RH are normally relayed via the corpus callosum to language centres in LH
Sperry
recognition by touch
object shown to LVF
- could not name them but could select a matching object using left hand (connected to RH receiving info from LVF)
- left hand could also select an object that was associated with image presented to the IVF
in each case, the person could not verbally identify what they had seen bit could understand what the object was (using the RH) and select the corresponding object.
Sperry
composite words
2 words presented on either side of the visual field e.g key presented to the left and ring to the right)
patient:
- writes key with the left hand (goes to RH linked to LVF)
- says the word ring (RVF linked to LH)
Sperry
matching faces
composite pictures made up of 2 different halves of a face was presented (one half to each hemisphere)
- LH dominated the verbal description
- RH dominated the selection of a matching picture.
evaluation of split brain research into hemispheric lateralisation
strengths
- research shows laterlised brain functions. the left hemisphere is analytical and verbal (the analyser) and the right is adept at spatial tasks and music (the synthesiser). the right hemisphere can only produce basic words and phrases but contributed emotional content to language. distinction may be too simplified and several tasks associated with 1 hemisphere can also be carried out by the other.
- methodology. sperry used a carefully standardised procedure. participants stated at a fixed point with one eye. an image flashed up for 0.1 seconds so the patient had no time to move their eyes over the image. this allowed sperry to vary aspects of the basic procedure. well controlled procedure.
- started a debate about the nature of the brain. triggered a theoretical and philosophical debate about the nature of conscious and degree of communications. some suggest hemisphere are so functional different they represent a form of duality in the brain.
evaluation of split brain research into hemispheric lateralisation
limitations
- generalisation. split brains patients are a very unusual sample of people. only 11 patients took part in all variations all had a history of seizures. this may have caused unique changes to the brain influencing the findings. the limits the extent to which the findings can be generalised to normal brains, reducing validity
- differences in hemispheric functions overstated. growing body of pop-psychological literature that oversimplifies and overstates the difference in functions between the 2 hemispheres. modern neuroscientists argue these distinctions are not all clear cut. may behaviours performed by one hemisphere can be performed by the other when required. the apparent flexibility of the 2 hemispheres suggests some of the conclusions drawn are too simplistic.
what are the purpose of medical techniques used to investigate the brain
techniques for investigating the brain are often used for medical purposes in the diagnosis of illness
the purpose of scanning in psychological research is often used to investigate localisation - to determine which parts of the brain do what.
what are 4 methods used to investigate the brain
- fMRI
- EEG
- ERPs
- post mortem
fMRI
highlights active areas of the brain
functional magnetic resonance imaging
detects changes in blood oxygenation and flow that occur due to neural activity in specific brain areas.
when a brain area is more active it consumes more oxygen and blood flow is directed to the active area (haemodynamic response)
fMRI produces a 3D mage showing which parts of the brain are active and therefore must be involved particular mental processes.
evaluation of fMRI
- non invasive. unlike other scanning techniques does not rely on the use of radiation and is safe.
- it produces images with high spatial resolution showing detail by the millimetre. this means fMRI can provide a clear picture of how brain activity is localised.
- fMRI is expensive compared to other techniques and can only capture a clear image of a person if they stay still
- it has poor temporal resolution because of 5 second lag between initial neural activity and image. this means fMRI may not truly represent moment to moment brain activity
EEG
Electroencephalogram (EEG)
shows overall electrical activity
measures electrical activity within the brain via electrons using a skull cap
the scan recording represents the brainwave patterns generated from millions of neurons. this shows overall brain activity
EEG is often used as a diagnostic tool. for example unusual arrhythmic patterns of brain activity may indicate abnormalities such as epilepsy, tumours or sleep disorders.
evaluation of EEGs
- contributed to our understanding of the stages of sleep
- has extremely high temporal resolution. EEgs can detect brain activity at a resolution of a single millisecond.
- invaluable in diagnosing conditions such as epilepsy
- EEG produces a generalised signal from thousands of neurons. So it is difficult to know the exact source of neural activity. Cant distinguish between the activity of different but adjacent neurons.
ERPs
event related potentials (ERPs)
brainwaves related to particular event
is what is left when all extraneous brain activity from an EEG recording is filtered out.
this is done using a statistical technique, leaving only those responses that relate to the presentation of a specific stimulus or performance of a certain task.
ERPs are types of brainwave that are triggered by particular events
research has revealed many different forms of ERP and how these are linked to cognitive processes.
evaluation of ERPs
- ERPs are more specific than can be achieved using raw EEG data.
- they have excellent temporal resolution especially compared to fMRI
- lacks standardisation in methodology between studies. this makes it difficult to confirm findings in studies involving ERPs.
- background noise and extraneous material must be completely eliminated. this may not always be easy to achieve.
Post mortem examinations
a technique involving the analysis of a person’s brain following their death
areas of the brain are examined to establish the likely cause of a deficit or disorder that the person suffered in life
this may also involve comparison with a neurotypical brain in order to asses the extent of the difference.
post mortem evaluation
- Broca and Wernicke both relied on post mortem sutides.
- post mortem studies improve medical knowledge. they help generate hypotheses for further study.
- observed damage in the brain may not be linked to the deficits under review but to some other related trauma or decay.
- raise ethical issues of consent from the patient before death.
patients may not be able to provide informed consent.
what is a circadian rhythms
circa meaning about and diem meaning day
rhythms that last for 24 hours
biological rhythms are periodic activity governed by
- endogenous pacemakers (internal biological clocks)
2. exogenous zeitgebers. (external changes in the environment)
what is the sleep wake cycle governed by?
there is a basic rhythm governed by the superchiasmatic nucleus (SCN), which lies just above the optic chiasm and receives information about light directly from this structure.
the exogenous zeitgeber (light) can reset the SCN
Siffre cave study
demonstrated a free running circadian rhythm of about 25 hours.
French caver Shiffre spent long periods in dark caves to examine the effects of free running biological rhythms - 2 months (in 1962) in the caves of the southern alps and 6 months (in the 1970s) in a texan cave (when he was 60)
in each case study, Shiffre’s free running circadian rhythm settled down just above the usual 24 hours. importantly, he did have a regular sleep/wake cycle
Aschoof and Wever
a group of participants spent 4 weeks in a world war 2 bunker deprived of natural light
all but one (whose sleep wake was 29 hours) displayed a circadian rhythm between 24 and 25 hours
Siffre’s experience and the bunker study suggest that the natural sleep/ wake cycle may be slightly longer than 24 hours but is en-trained by exogenous zeitgebers associated with our 24 hour day.
Folkard et al.
endogenous pacemakers may have a stronger influence
studied a group of 12 people who lived in a dark cave for 3 weeks, going to bed when the clock said 11.45pm and waking when it said 7:45am
the researchers gradually speeded up the clock (unbeknown to the participants) so an apparent 24 hour day eventually lasted only 22 hours.
only 1 participant comfortably adjusted to the new regime. this suggests the existence of a strong free running circadian rhythm that cannot easily be overridden by changes in the external environment.
evaluation of circadian rhythms
strengths
- practical application to shift work. Shift workers experience a lapse of concentration around 6am so mistakes and accidents are ore likely, research suggested a link between shift work and poor health, with shift workers 3 time more likely to develop heart disease. thus research have economic implications.
- practical application to drug treatments. circadian rhythms coordinate the bodies basic processes with implications for pharmacokinetics.
evaluation of circadian rhythms
limitations
- case studies and small sample sizes. use of small groups or single individual. participants not representative of wider population limiting meaningful generalisations. Siffre clock slower at 60. even when 1 person involved many factors prevent general conclusions
- poor control. participants deprived of natural light but still had artificial light assumed to have no effect. adjust circadian rhythm from 22 to 28 hours using dim lighting. artificial lighting confounding variable.
- individual differences. individuals vary from 13 to 65 hour cycles. some display natural preference for sleeping and rising early others vis versa. age effects sleep wake patterns. findings may not fully represent individual differences within population
infradian rhythm
biological rhythm that lasts longer than 24 hours
they can be weekly monthly or yearly
the female menstrual cycle is a monthly infradian rhythm
seasonal affective disorder is a yearly infradian rhythm
female menstrual cycle
is an infradian rhytm
rising levels of oestrogen cause the ovary to develop and release an egg (ovulation)
then progesterone helps the womb lining to thicken, readying the body for pregnancy.
if pregnancy does not occur, the egg is absorbed into the body and the womb lining comes away and leaves the body (menstrual flow)
exogenous zeitgebers on the female menstrual cycle
study by Stern and McClintock (1998)
studied 29 women with irregular periods.
pheromones were taken from some at different stages of their cycles, via a cotton pad under their armpits.
these pads were then cleaned with alcohol and latter rubbed on the upper lips of the other participants
68% of women experienced changes to their cycle which brought them closer to the cycle of their odour donor.
SAD
seasonal affective disorder
is an infradian rhythm
a depressive disorder (low mood and activity) with a seasonal pattern.
symptoms are triggered during the winter months when the number of daylight hours becomes shorter.
SAD is an infradian rhythm called a circannual (yearly) cycle.
what causes SAD
during the night, the pineal gland secretes melatonin until dawn when there is an increase in light.
during winter, the lack of light in the morning means secretion goes on for longer.
this has a knock of effect on the production of serotonin in the brain (low serotonin is liked to depressive symptoms)
ultradian rhythms
rhythms that last less than 24 hours
stages of sleep is an example of an ultradian rhythm
stages of sleep
ultradian rhythm
sleep pattern occurs in 90 minute periods
divided into 5 stages, each characterised by a different level of brainwave activity (monitored using EEG)
stages 1 & 2: light sleep
person may be easily woken. brainwaves become slower and more rhythmic (alpha waves), slowing further as sleep becomes deeper (beta waves)
stages 3 & 4: deep sleep / slow wave sleep
hard to rouse someone. characterised by delta waves which are slower still and have a greater amplitude
stage 5: REM sleep. Rapid Eye Movement
fast, jerky activity of eyes. body paralysed yet brain activity speeds up.
evaluation of infradian rhythms
- research on menstrual cycle shows evolutionary value. advantageous for females to menstruate together and become pregnant same time so offspring could be looked after collectively increasing survival. validity of this perspective produce competition for highest quality males lowing fitness of potential offspring. avoidance of synchrony would be adaptive evolutionary.
- limitation in methodology. factors that may change menstrual cycle as confounding variables. what we would expect to occur by chance. small sample, self reporting onset may be inaccurate. lack validity
- animal studies. role of pheromones of animal sexual behaviour well documented, evidence for the effect in humans is speculative and inconclusive
- practical application. SAD photo therapy stimulates strong light resetting melatonin levels. relieve symptoms in 60% if sufferers placebo effect of 30%. cast doubt on the value.
evaluation of ultradian rhythms
- evidence support qualitatively different stages of sleep
monitored sleep patterns of 9 participants in sleep lav found evidence for stages of sleep. REM activity during sleep correlated with dreaming; brain activity varied according to how vivid the dreams were; when woken immediately they could accurately recall.
suggests REM sleep is a distinct ultraidan rhythm and is important component of the ultradian sleep cycle.
endogenous pacemakers
internal mechanisms that govern biological rhythms
although they are internal biological clocks they can be affected by the environment.
the most important one is the suprachiasmatic nucleus involved in the sleep wake cycle.
suprachiasmatic nucleus (SCN)
an endogenous pacemaker
is a tiny bundle of nerve cells in the hypothalamus which helps maintain circadian rhythms (sleep wake cycle)
nerve fibres from the eye cross at the optic chiasm on their way to the visual cortex. The SCN lies just above the optic chiasm and recieves information about light from this structure.
It is closely linked with the pineal gland as it passes information on day length to the pineal gland
influence of SCN on the sleep wake cycle
DeCoursey et al (2000)
destroyed SCN connections in the brain of 30 chipmunks which were returned to their natural habitat and observed for 80 days.
their sleep wake cycle disappeared and many were killed by predators.
influence of SCN on sleep wake cycle
Ralph et al (1990)
bred mutant hamsters with a 20 hour sleep / wake cycle.
SCN cells were transplanted from the foetal tissue of these hamsters into the brains of normal hamsters, which then developed cycles of 20 hours.
pineal gland
endogenous pacemaker involved in the sleep wake cycle
the SCN passes information on day length to the pineal gland which increases production of melatonin during the night
melatonin is a hormone that induces sleep and is inhibited during periods of wakefulness. It has also been suggested as a causal factor in seasonal affective disorder.
exogenous zietgebers
influence biological rhythms. these can be described as environmental events that are responsible for resetting the biological clock of an organism
exogenous zietgebers involved in the sleep wake cycle
- light
- social cues
entrainment
process of resetting biological clocks
without external cues the free running biological clock continues in a cyclical pattern.
Zeitgebers reset the sleep wake cycle: an interaction of internal and external factors
exogenous zietgeber
light
light can reset the body’s main endogenous pacemaker (SCN) and also has an indirect influence on key processes in the body controlling hormone secretion and blood circulation etc.
exogenous zietgeber - light
Campbell and Murphy
woke 15 participants at various times and shone a light on the backs of their knees, producing a deviation in the sleep wake cycle of up to 3 hours.
light is a powerful exogenous zeitgeber detected by skin receptors sites and does not necessarily rely on the eyes to influence the SCN
exogenous zietgeber - social cues
the sleep wake cycle is fairly random in human newborns, but most babies are entrained by about 6 weeks.
schedules imposed by parents are a key influence, including adult determined mealtimes and bedtimes.
research also shows adapting to local times for eating and sleep (not responding to ones own feelings of hunger and fatigue) entrains circadian rhythms and tackles jet lag.
evaluation of edogenous pacemakers
- research into SCN obscures other body clocks. body clocks (peripheral oscillators) are found in many organs and cells they are influenced by the SCN but act independently changing feeding patterns in mice altered circadian rhythms of cells in the liver by up to 12 hours, leaving SCN rhythm unaffected. many other complex influences.
- use of animals. hard to generalise findings because cognitive factors more significant in humans. ethics involved. exposed to great harm and potential risk. does benefits justify procedures used.
evaluation of exogenous zeitgebers
- influence overstated. case of a man blind from birth with a 24.9 hour cycle. could not adjust to social cues so he took sedatives and stimulates. studies of people in Arctic regions show normal sleep patterns despite prolonged exposure to light.
- methodological issues. campbell and murphy’s study not been replicated some light exposure to participants eyes confounding variable. isolating one zietgeber does not give us insight into the many others. ignored and underplay the way these zeitgebers interact
- endogenous pacemakers and exogenous zeitgebers interact.
only in exceptional circumstances do pacemakers free run unaffected by zeitgebers. total isolation experiment are rare and present an unrealistic view. as they interact in real life it makes little sense to separate them
