biopsychology

the nervous system

-our primary internal communication system made of specialised network of cells

-based on electrical and chemical signals (unlike endocrine system - based on hormones)

the nervous system’s two main functions and its two subsystems:

-to collect, process and respond to environmental stimuli

-to co-ordinate the working of different organs and cells in the body

made up of the central nervous system (CNS), and the peripheral nervous system (PNS)

the central nervous system

-made of the brain and spinal chord

-brain is the center of all conscious awareness; its outer layer (the cerebral cortex) is 3mm thick and covers the circumference of the brain. the brain is highly developed in humans and is what distinguished our higher mental functions from those of other animals. it is divided into two hemispheres.

-the spinal cord is an extension of the brain stem. it passes messages to and from the brain and connects nerves to the PNS. its responsible for reflex actions (eg pulling ur hand away from a hot plate)

the peripheral nervous system (PNS)

-transmits messages (via millions of neurons (nerve cells)) to and from the CNS. the PNS is further subdivided into the:

• automatic nervous system (ANS), which governs vital functions in the body (like breathing, heart rate, digestion, sexual arousal and stress responses)

• somatic nervous system (SNS), which govern muscle movements and retrieves information from sensory receptors

the endocrine system

-works with nervous system to control body vital functions, and acts more slowly than the nervous system but produced in large quantities, disappear quickly and have widespread, diverse and powerful effects. 

-glands are organs that synthesise hormones; biochemical substances that circulate the blood to affect target organs (with receptors to that hormone (e.g. thyroid produces thyroxine- affects heart cells to increase heart rate, and body cells to increase metabolic rates (affects growth rates)). 

-the pituitary gland is often referred to as the ‘master gland’ because it controls the release of all other endocrine gland’s hormones

endocrine and ANS

endocrine system and the ANS work in parallel when a stressor is perceived: hypothalamus instantly activates pituitary gland, triggering activity in the sympathetic branch of the automatic nervous system. the ANS changes from its normal resting state (the parasympathetic nervous system) to the physiologically aroused sympathetic state.

the two subsystems are antagonistic to each other.

the endocrine system and ANS

fight or flight 

-adrenaline is released from the adrenal medulla into bloodstream to trigger physiological changes, creating the psychological arousal necessary for fight or flight

physiological changes are increased breathing and heart rate, dilated pupils, inhibited digestion and saliva production, and contracted rectum.

parasympathetic action: when threat passes, parasympathetic nervous system returns body to resting state by reducing changes that were induced by the sympathetic branch (rest and digest response).

neurons

the structure and functions of neurons

-transmit signals chemically and electrically to provide the nervous system its primary means of communication.

-types: sensory, relay and motor

the structure of neuron

-the cell body (soma) includes a nucleus, containing cell’s genetic information. dendrites (branchlike structures) protrude from soma to carry impulses from neighboring neurons toward the soma.

-axon carries impulses away from soma to length of neuron, and is covered in a interval (nodes of ranvier) fatty layer of myelin sheath that protects it and speed electrical transmission (forces it to jump across the gaps along the axon)

-end of neuron is the terminal buttons that communicate with the next neuron in chain across a synapse

location of neurons

-cell bodies of motor neurons are in CNS but have long axons which form part of the PNS. sensory neurons are located outside the CNS, in the PNS in a cluster known as ganglia. relay neurons make up 97% of all neurons and most are found in the brain and visual system

electrical transmission- the firing of a neuron

-when a neuron is in resting state, the inside of the cell is negatively charged compared to the outside. when it’s activated by stimulus, the inside becomes positively charged for a split second causing an action potential to occur, creating an electrical impulse that travels down the axon towards the terminal.

synaptic transmission

chemical transmission

neurons communicate within neural networks, separated by synapses.

-signals within neurons are transmitted electrically and signals between neurons are transmitted chemically across the synapse.

-when the electrical impulse reaches the presynaptic terminal, it triggers the release of neurotransmitters from synaptic vesicles.

-insert pic

synaptic transmission

neurotransmitters

-brain chemical released from synaptic vesicles that relay signals by diffusing across the synapse from one neuron to another.

once is crossed the gap, it’s taken up by a postsynaptic receptor site on the dentrites of the neuron (axons take signals to the synapse, dentrites take them away). the chemical message is converted back into an electrical impulse and the process of transmission begins again in this other neuron.

-direction of travel can only be one way because they’re released by presynaptic neuron terminal and received by the postsynaptic neuron at receptor sites.

-each neurotransmitter has its own specific molecular structure that fits perfectly into a synaptic receptor site (lock and key), each has a specific function.

synaptic transmission

excitation and inhibition

-neurotransmitters have an excitatory or inhibitory effect of the neighbouring neuron

-excitation: increases positive charge of the postsynaptic neuron, increasing the likelihood that it will fire the electrical impulse (eg adrenaline)

-inhibition: increase the negative charge of the postsynaptic neuron, decreasing the likelihood that it will fire. (eg serotonin)

synaptic transmission

summation

the excitatory or inhibitory influences are summed and if the net effect is excitatory, it is more likely to fire (inside of postsynaptic neuron temporarily becomes charged) vice versa. once an impulse is created it travels down the neuron.

the action potential of the synaptic neuron is only triggered if the sum of the excitatory and inhibitory signals at one time reaches the threshold.

localisation of function of the brain

localisation vs holistic theory

scientists generally accepted the holistic theory of the brain (all parts were involved in the processing of thought and action)

in contrast broca and wernicke discovered specific areas of the brain are associated with particular physical and psychological functions, and argued for localisation of function; idea that different parts of the brain perform different tasks and are involved with different parts of the body, and so if a certain part of the brain becomes damaged the function associated with that area will be affected

localisation of function

hemispheres of the brain

the cerebrum is divided into two symmetrical halves; the left and right hemispheres. some of our physical and psychological functions are controlled or dominated by a specific hemisphere (lateralisation). as a general rule, activity on the left of the body is controlled by the right hemisphere and activity on the right is controlled by the left hemisphere.

localisation of function

brain lobes

the lobe is a part of an organ that is separate in some way from the rest. wach brain in the cerebral cortex in the brain is associated with different functions.

• the frontal lobe: (in both hemispheres) the motor area, which contains voluntary movement (motor control) in the opposite side of the body. damage to this area may result in 

• the parietal lobe: in the somatosensory area, where sensory information from the skin is represented (the amount of this area devo

• the occipital lobe

• the temporal lobe

localisation of function in the brain

the language centres of the brain

-language is restricted to the left hemisphere in most people

broca (1880s) identified a brocas area (left frontal lobe) responsible for speech production. damage causes brocs aphasia (slow laborious speech that lacks fluency, and usually difficult with propositions). patient ‘tan’.

wernicke (1880s) showed damage to wernickes area had no problem producing language (fluent but meaningless speech) but difficulty understanding it, meaning the area was responsible for language comprehension. damage led to wernickes aphasia leads to producing nonsense words as part of their speech

localisation of function in the brain

evaluation: strengths

-practical psychiatry benefits: neurosurgery treating OCD where the cingulate gyrus is isolated from the rest of the brain for OCD. dougherty et al (2002) 44 people where after a followup, 30% has met the criteria for a successful response and 14% for a partial response. this procedure suggests brain function may be localised

-brain scans show wernickes area active during listening task and brocs area active during reading task petersen (1988). buckner and petersen (1996) revealed semantic and episodic memories reside in different parts of the prefrontal cortex, confirming localisation for everyday behaviours.

-phineas gage suffered damage to frontal lobe from metal rod (area responsible for personality, executive decisions like self control and decision making), led to dramatic personality shift from calm and respected to outbursts, disrespect and inappropriate behaviour) - single case study, but real evidence that influenced other findings.

localisation of function in the brain

evaluation: limitations

lashley (1950) removed areas of cortex (between 10 and 50%) in rats learning the route through a maze and showed no area proved to be more important than any other area for learning the route, showing learning process requires every part of the cortex rather than being confined to a particular area. suggests more demanding cognitive processes are holistic.

dick and tremblay (2019-6) found only 2% of modern researchers think language in the brain is completely controlled by broca’s and wernicke’s areas. advances in fMRI mean neural processes can be studied with more clarity than ever, suggesting language can be more holistic, contradicting localisation theory.

hemispheric lateralisation

-idea that the two brain hemispheres are functionally different and certian mental processes and behaviours and primarily controlled by one hemisphere

left (LH) and right (RH) hemispheres

-language is believed to be localised to left hemisphere as RH only produces rudimentary words words and phrases and contributes to emotional context of conversations

hemispheric lateralisation evaluation

split brain research

split brain operation involves severing the corpus callosum; the connection between the RH and LH (surgical procedure to reduce epilepsy when excessive electrical activity travels across hemisphere. split brain research shows how the hemispheres function when they can’t communicate.

split brain research studies

roger sperry (1968) 11 p’s who had split brain operations

split brain research evaluation

plasticity

brain plasticity

describes the brains tendency to change and adapt as a result of experience and new learning, generally involving the growth of new synaptic connections.

as we age, we undergo synaptic pruning (rarely used connections are deleted and frequently used connections are strengthened) - enables life long plasticity where new neural connections are formed in response to new demands on the brain.

plasticity

research into plasticity

maguire et al (2000) studies brains of london taxi drivers, found significantly higher grey matter volume in posterior hippocampus than matched control group (after taking ‘the knowledge’, a complex test on memory of city navigation-found to alter the brain structure). longer time having the job meant more pronounced structural difference (+ correlation)

-draganski et al (2006) imaged medical students’ brains 3 months before and after their final exams. learning-induced changes occurred in posterior hippocampus and parietal cortex, presumably as a result of learning.

plasticity

evaluation

age: bezzola et al (2012) demonstrated how 40 hours of golf training produced changes in the neural representations of movement in p’s aged 40-60. increased motor cortex activity in the novice golfers compared to control group, suggests more efficient neural changes after demand and plasticity continues throughout life.

research support from hubel and wiesel (1963) learned sewing kittens eye shut, the visual cortex in the brain from the closed eye continued to process visual information.

brains adaption to prolonged drug use leads to poorer cognitive function in later life (medina et al 2007) - also a link to phantom limb syndrome (ramachandran and hirstein 1998) so brain’s ability to adapt to damage is not always beneficial.

research suggests seasonal plasticity in the brain in response to environmental changes (eg SCN seen to shrink in all animals during spring and expands throughout autumn (tramontin and brenowitz 2000) - studies have been done mostly on songbirds, human behaviour may be controlled differently, anthropomorphic bias. 

functional recovery of the brain after trauma

following any injury, healthy unaffected areas of the brain are often able to adapt and compensate for the damaged, destroyed or missing, areas. the functional recovery is an example of neural plasticity.

this can occur quickly after trauma (spontaneous recovery) and then slow down for several weeks or months, where than the individual may require rehabilitative therapy for their recovery.

funcitonal recovery of the brain

the brain can rewire and reorganise itself by forming new synaptic connections near damaged areas (like avoiding roadworks on the way to school by finding a different route)- secondary neural pathways that wouldn’t typically be used to carry out that function are activated to enable functioning to continue (doidge 2007). includes

• axonal sprouting: growth of new nerve endings which connect with other undamaged nerve cells to form new neural pathways.

• denervation supersensitivity: occurs when axons that do a similar job becomes aroused to a higher level to compensate for the ones that are lost (can have negative consequences if oversensitivity leads to messages like pain)

• recruitment of homologous (similar) areas on the opposite side of the brain: if damage to brocas area, the right sided equivalent would carry out its functions.

functional recovery of the brain after trauma

evaluation

real world application: understanding plasticity processes contributed to the field of neurorehabilitation: understanding that axonal growth is possible encourages new therapies to try (eg constrained-induced movement therapy for stroke patients) shows practical value in medicine as professionals will know when interventions need to be made.

cognitive reserve: level of education may influence recovery rates (schneider et al 2014)- people with higher education greater their chances of a disability free recovery.

small samples: most studies draw conclusions based on small number of participants and no control group, fairly typical of research on functional recovery.

ways of studying the brain: the purpose and the types

scanning in psychological research is often to investigate localisation

types:

• functional magnetic resonance imaging (fMRI)

• electroencephalogram (EEG)

• event-related potential (ERP)

• post-mortem examinations

functional magnetic resonance imaging (fMRI)

-works by detecting changes in blood oxygenation and flow that occur as a result of neural activity in specific parts of the brain: activated brain regions consume more oxygen and to meet this demand, blood flow is directed there (the haemodynamic response)

-uses magnetic fields to monitor changes, creating detailed 3D map of active brain regions (activation maps) during cognitive tasks or in response to stimuli to know which parts of the brain are involved in particular processes, important implications for understanding localisation of function.

strengths of fMRI

-doesnt rely on the use of radiation, virtually risk free (if administered correctly), non-invasive and straightforward to use

-produces images that have high spatial resolution (depicts detail by the millimetre), and provides a clear picture of how brain function is localised, means fMRI can safely provide a clear picture of brain activity

limitations of fMRI

-expensive in comparison to other neuroimaging techniques

-poor temporal resolution (around a 5s time difference in brain activity and detection) so may not represent moment-to-moment brain activity.

electroencephalogram (EEG)

measures electrical activity in the brain via electrodes fixed to scalp using a skull cap. the scan recording represents the brainwave patterns generated from the action of thousands of neurones, providing an overall account for brain activity.

-often used as a diagnostic tool for unusual arrhythmic patterns for neurological abnormalities like epilepsy, tumours and sleep disorders.

strengths of EEGs

-useful in studying stages of sleep, and the diagnosis of epilepsy (characterised by random bursts of activity in the brain that can be easily detected using EEGs), showing real world use.

-extremely high temporal resolution (some technology can accurately detect brain activity at a resolution of a single millisecond) 

limitations of EEGs

-generalised nature of information received (from thousands of neurones)

-poor spatial resolution: not useful for pinpointing the exact source of neural activity and so doesn’t allow researchers to distinguish between activities originating from different but adjacent locations.

event-related potentials (ERPs)

EEG data has all the neural responses associated with specific sensory, cognitive and motor events that are of interest to cognitive neuroscientists. 

using a statistical averaging technique, all extraneous brain activity from the original EEG recording is filtered out, leaving only responses that relate to the presentation of a specific stimuli or performance of a specific task. what remains is ERPs (type of brainwave triggered by particular events). can be used to study attention, perception, memory and language.

strengths of ERPs

-more specificity to to the measurement of neural processes than could ever be achieved using raw EEG data.

-derived from EEG so have amazing temporal resolution, allowing them to be frequently used to measure cognitive functions and deficits such as the allocation of attentional resources and the maintenance of the working memory

limitations of ERPs

-lack of standardisation has been pointed out of methodology between different research studies that make it difficult to confirm findings 

-requires all extraneous variables to be eliminated, not always easy to achieve

-requires many trials

post-mortem examinations

-invasive analysis or CT scan of a person following their death.

-usually used in psychological research for rare disorders and have experienced unusual deficits in cognitive processes or behaviour.

-examining areas of damage can establish cause of affliction the person experiences and can be compared with a neurotypical brain to ascertain the extent of the difference

-can also be used to determine cause of death in regular cases

strengths of post-mortem examinations

-vital for providing a foundation for early understanding of key processes in the brain (broca and wernicke) relied on post-mortem studies to establish links between language, brain and behaviour decades before the availability of neuroimaging. 

limitations of post-mortem examinations

-brain is no longer active so only structure can be observed

-findings may be affected by post-mortem changes and causation issue as damage may not be linked to the deficits under review, but rather unrelated trauma or decay

-ethical issues as may not always be able to attain consent, challenging the usefulness of post-mortem studies in psychological research (HM was unable to give consent but still had his brain checked)

biological rhythms: circadian rhythms

biological rhythms exert an important influence on the way our body systems behave.

all biological rhythms are governed by:

• endogenous pacemakers: internal body clocks

• exogenous zeitgebers: external changes in the environment

biological rhythms: circadian rhythms

the sleep/wake cycle

the effect of daylight (an exogenous zeitgeber) on our sleep/wake cycle is demonstrated when we feel tired at night and alert during the day.

-the sleep/wake cycle is also governed by am endogenous pacemaker - a biological clock called the SCN, which lies just above the optic chiasm, which provides information from the eye about light. light input can reset the SCN

biological rhythms: circadian rhythms

siffre’s cave study

michel siffre spent an extended period of time underground to study the effects on his biological rhythms after being deprived of exposure to natural light and sound, with access only to sound and communication. he resurfaced mid-september 1962 believing it was mid-august. his free running biological rhythm settled to one just over 24hours though he continued to sleep and wake at a regular schedule.

biological rhythms: circadian rhythms

the bunker study

aschoff and wever (1976) - group of p’s to spend four weeks in a ww2 bunker deprived of natural light. all but one displayed a circadian rhythm between 24 and 25 hours. these studies suggest our natural sleep/wake cycle may be slightly longer than 24h but is entrained by exogenous zeitgebers associated with our 24h day.

biological rhythms: circadian rhythms

other research

despite this, we shouldn’t overestimate the effects of exogenous zeitgebers on our internal biological clock: folkard (1985) studied 12 p’s who lived in a dark cave for 3 weeks, going to bed when clock said 11:45pm and rising at 7:45am, not knowing the researchers would gradually speed up the clock (for a 22hour day) - only 1 p comfortably adjusted to the new regime, suggesting the existence of a strong free-running circadian rhythm that cannot be easily overridden by exogenous zeitgebers.

biological rhythms: circadian rhythms

other research

dont need to remember this

-core body temp varies across the course of the day. evidence suggests body temperature can have an effect on mental abilities (warmer means better cognitive abilities)

folkard (1977) demonstrated children who were read stories to them at 3pm showed superior recall the next week than those read stories at 9am. similarly, gupta (1991) found improved performance on IQ tests when p’s were assessed at 7pm as oppose to 2pm and 9am.

biological rhythms: circadian rhythms

evaluation: strengths

-provides understanding of adverse consequences that occur when circadian rhythms are disrupted (desynchronisation) e,g. night workers experience reduced concentration at 6am (a circadian trough) meaning mistakes and accidents are more likely (boivin et al 1996). research also suggests relationship between night shift work and poor health (x3 more likely to develop heart disease) (knutsson 2003), demonstrating practical economic implications this research has on how to manage worker productivity.

counterpoint: only a correlation has been established, not a cause-and-effect relationship. solomon (1993) suggests high divorce rates in night shift workers may be to deprived sleep and absence at family events, suggesting it may not be a biological factor creating adverse consequences associated with shift work.

-used to improve medical treatments: circadian rhythms co-ordinate multiple bodily basic processes such as heart rate, digestion and hormone level, which rise and fall across the day which has led to the chronotherapeutics field (how medical treatment can be administered in synchrony with biological rhythms. bonten et al 2015 research into how aspirin for heart attacks should be taken last thing at night for maximum chance reduction of heart attack.

biological rhythms: circadian rhythms

evaluation: limitations

-generalisations are difficult to make: (aschoff and wever, siffre) studies based on very small samples, which each showed that sleep/wake cycles vary from person to person, czeisler (1999) found individual differences varying from 13 to 65 hours. duffy (2001) found some people have natural preferences for going to bed early and rising early (larks) or opposite (owls). 

-siffre used a lamp which couldve altered his circadian rhythm

siffre found, in a later 1999 study, his sleep/wake cycle slowed down with age, meaning its difficult to use the research data to discuss anything more than averages, which is quite useless. 

biological rhythms: circadian rhythms

evaluation: other relevant research

suggested the school day should be shifted for later hours to adjust to the teenage chronotype. research has shown benefits for academic and behavioural performance when lessons start later in the day, including reduced dependence on caffeine (adolescence sleep working group 2014)

-however it would be disruptive for parents and teachers and limits opportunity for extra-curricular activity.

types of biological rhythms

infradian rhythms: type of biological rhythm with a frequency of less than one cycle in 24 hours

ultradian rhythms: frequency of more than one cycle in 24 hours, such as cycles of sleep

biological rhythms: infradian rhythms

the menstrual cycle

governed by monthly changes in hormone levels that regulate ovulation. the cycle refers to the time between the first day of the period where the womb lining in shed to the day before the next period, typically lasting 28 days. during each cycle, rising levels of oestrogen cause the ovaries to develop an egg and release it. after ovulation, progesterone helps the womb lining grow thicker, readying the womb for pregnancy, where if it doesnt occur, the egg is absorbed into the body and the womb lining leaves the body (menstrual flow).

biological rhythms: infradian rhythms

synchronising the menstrual cycle

although the menstrual cycle is endogenous, evidence suggests it is influenced by exogenous factors, such as the cycles of other women. stern and mcclintock (1998) demonstrates how menstrual cycles may synchronise due to the influence of pheromones by studying 29 women with a history of irregular periods. pheromone samples (via a cotton pad placed on their armpit, worn for at least 8 hours to ensure the pheromones were picked up) was collected by 9 of the women at different stages of their menstrual cycle, which was treated and put on the upper lip of the other women. research found 68% of p’s experienced changes in the cycles that brought them closer to their ‘odour donor’.

biological rhythms: infradian rhythms

seasonal affective disorder (SAD)

-(the winter blues) depressive order with a seasonal pattern of onset by DSM-5. persistent low mood and anhedonia, triggered by the winter months where number of daylight hours become shorter.

-circannual, although can be considered a circadian as the cause can be attributed to sleep/wake cycle disruption from prolonged daily darkness in winter

-psychologists theorise melatonin is involved in SAD as with lack of light in waking hours, the pineal gland secretes melatonin for longer, which is predicted to effect on serotonin production (linked to the onset of depressive symptoms).

biological rhythms: infradian rhythms

evaluation

-menstrual synchrony has evolutionary basis as it may have been advantageous for women to menstruate and become pregnant at the same time, allowing babies who lost their mothers after childbirth to have access to breast milk, increasing chances of survival, and for alloparenting purposes.

-methodological limitations: many factors can affect changes to menstrual cycle including stress, changes in diet and exercise, which may act as confounding variables in the research, could explain why ‘trevathan et al 1993’ failed to replicate these findings, suggesting menstrual synchrony studies are flawed

-SAD research has practical application: light therapy is used as a treatment (a box which stimulates very strong light to reset the bodys internal clock), which sanassi 2014 shows helps reduce the effects of SAD in 80% of people. its the preferred treatment over antidepressants as its regarded as safe. however, it can produce headaches and eye strain- and kelly rohan 2009 recorded a relapse rate of 46% over successive winters, compared to 27% in comparison group receiving CBT.

biological rhythms: ultradian rhythms

stages of sleep

psychologists identified five distinct sleep stages that altogether span approximately 90 minutes, this cycle repeats through the night. each stage is characterised by a different level of brainwave activity, monitored using an EEGs.

-stages 1+2: might be easily woken. brainwaves have high frequency and short amplitude (alpha waves). stage 2 differs due to occasional random changes in pattern called sleep spindles

-stage 3+4: (deep sleep) delta waves; lower in frequency and higher in amplitude: difficult to wake someone atp.

-stage 5 (REM (rapid eye movement) sleep) - body is paralysed but brain activity resembles that of the awake brain, dreaming is likely, theta waves are produced.

biological rhythms: ultradian rhythms

evaluation

-improved understanding of age related changes in sleep: sleep scientists observed stages 3 and 4 duration reduces with age, because growth hormones are mostly produced during these stages, which older people use less. cauter et al (2000), theorised the resulting sleep deficit may explain various issues in old age, such as reduced alertness. to increase this, relaxation and meditation is used, suggesting knowledge of ultradian rhythms has practical value.

-studying sleep in lab allows control over EVs: meaning researcher can exclude temporary variables such as noise and temperature that may affect sleep. however they involve p’s being connected to complicated machinery, not sleeping in a way that demonstrates their ordinary sleep patterns, lack of external validity

-a limitation is significant differences in variations between people. tucker et al (2007) found large differences between p’s for duration of each sleep stage, particularly 3 and 4, where he suggested these may be biologically determined, making it hard to describe ‘normal sleep’ in any meaningful way.

endogenous pacemakers and the sleep/wake cycle

the superchiasmatic nucleus (SCN)

-bundle of nerve cells located in the hypothalamus in each brain hemisphere.

-one of the primary endogenous pacemakers in mammals and is influential in maintaining circadian rhythms, like the sleep/wake cycle. the optic chiasm receives information about light from the SCN directly, which continues even when our eyes are closed, allowing the biological clock to adjust to changing patterns of daylight during sleep

endogenous pacemakers and the sleep/wake cycle

animal studies on SCN

decorusey et al (2000) destroyed the SCN connections in 30 chipmunks, returned them to their natural habitat and observed them for 80 days. their sleep/wake cycles disappeared and by then end, a significant amount had been killed by predators (presumably because they were awake, active and vulnerable to attack when they shouldve been asleep)

ralph et al (1990) took SCN cells from ‘mutant’ hamsters and put them into regular hamsters who had previously a normal circadian sleep, and showed their sleep/wake cycles changed to 20 hours

endogenous pacemakers and the sleep/wake cycles

the pineal gland and melatonin

SCN passes information on length of day and night that it receives to the pineal gland, an endogenous pacemaker of the sleep/wake cycle that releases melatonin (hormone that induces sleep at night and inhibits sleep in the day). has been suggested as a causal factor in SAD (seasonal affective disorder)

endogenous pacemakers and the sleep/wake cycle

evaluation: limitations

-may obscure other body clocks as research has revealed that there are numerous circadian rhythms in may organs and cells in the body (peripheral oscillators found in lungs, pancreas and skin) that are influenced by the SCN but also act independently. damiola et al (2000) demonstrated how changing mice’s feeding patterns could alter the circadian rhythms of liver cells by up to 12 hours, whilst leaving the SCN unaffected

-endogenous pacemakers cant be studied in isolation as in everyday life, pacemakers and zeitgebers interact and it may make little sense to separate the two for research purposes, lowers research validity 

-animal studies are justified because they have similar mechanisms (the SCN and pineal gland) however ethical considerations as decoursey study exposed animals to risk and most died as a result of the research (not protected from more harm than the average day)

exogenous zeitgebers and the sleep/wake cycle

-external factors that influence or entrain our biological rhythms. in the absence of external cues, our free running biological clock has a distinct cyclical pattern, but is entrained by environmental cues (interaction of internal and external factors)

exogenous zeitgebers and the sleep/wake cycle

light

can reset the body’s main endogenous pacemaker (SCN), thus playing an important role in the sleep/wake cycle, while having an indirect influence in key processes such as hormone secretion and blood circulation. campbell and murphy (1998) demonstrated light  can be detected by skin receptor sites on the body even when the same information isnt received by eyes: 15 p’s were woken at various times and light was shone on the back of their knees, suggesting light is an important exogenous zeitgeber

exogenous zeitgebers and the sleep/wake cycle

social cues

at about 6 week of age, circadian rhythms begin and 10 weeks later, their rhythms have been entrained by schedules imposed by parents, including adult-determined mealtimes and bedtimes

research on jet lag shows adapting to local eating and sleeping times (not responding to own hunger and fatigue feelings) can entrain circadian rhythms, beating lag - burgess et al (2003)

exogenous zeitgebers and the sleep/wake cycle

evaluation: limitations

-dont have the same effects for all; environments with little darkness in summer and little light in winter have similar sleep patterns all year around, suggesting sleep/wake cycles are primarily controlled by endogenous pacemakers that can override environmental changes in light

-miles et al (1977) study of blind man from birth with abnormal 24.9 circadian rhythm despite social cues like regular mealtimes., suggesting social cues alone arent effective in resetting biological rhythms.

-people have poorer sleep quality with age hood et al (2004) found insomnia management in elderly was improved with more exercise and exposure to natural light