BIOPSYCHOLOGY RECAP -
THE NERVOUS SYSTEM -
the nervous system is a specialised network of cells in the human body and is our primary internal communication system
it is based on electrical and chemical signals, whereas other systems such as the endocrine is based on hormones
it has two main functions -
to collect, process and respond to different organs and cells in the body
to co-ordinate the working of different organs and cells in the body
the nervous system is split into two subdivisions -
the central nervous system (CNS)
the peripheral nervous system (PNS)
THE CENTRAL NERVOUS SYSTEM (CNS) -
the CNS is made up of the spinal cord and the brain
BRAIN - the centre of conscious awareness, its highly developed and its split into two hemispheres (left and right)
SPINAL CORD - an extension of the brain, that passes messages to the PNS from the brain, and its also responsible for reflex actions
THE PERIPHERAL NERVOUS SYSTEM (PNS) -
the PNS transmits messages via millions of neurones, to and from the central nervous system
the nervous system is further divided into the -
AUTONOMIC NERVOUS SYSTEM - governs vital functions in the body such as breathing, heart, rate, digestion, sexual arousal and stress responses
SOMATIC NERVOUS SYSTEM - governs muscle movement and receives information from sensory receptors
the autonomic nervous system then divides further into -
SYMPATHETIC NERVOUS SYSTEM - this alerts the body to threats and prepares it for the flight or fight response (EG increase in heart and breathing rate, inhibited digestion and sweating)
PARASYMPATHETIC NERVOUS SYSTEM - carries signals to relax the bodies systems back to its resting state (rest and digest response)
THE ENDOCRINE SYSTEM -
GLANDS AND HORMONES -
the endocrine system works alongside the nervous system to control vital functions in the body
the endocrine system acts more slowly than the nervous system but has very widespread and powerful effects
various glands in the body produce hormones that are secreted to the blood stream and affect any cell in the body that has a receptor for that particular hormone
most hormones affect cells in more than one body organ, leading to diverse powerful responses
some examples of endocrine glands and the hormones they produce are -
PITUITARY - master gland, controls the other endocrine glands
TESTES - releases testosterone
OVARIES - releases oestrogen
ADRENAL - releases adrenaline
THYROID - releases thyroxine
ENDOCRINE AND ANS WORKING TOGETHER -
often the endocrine system and ANS work in parallel with each other, normally in a stressful event
EG if you become scared, the hypothalamus activates the pituitary gland and this triggers activity in the sympathetic nervous system, this makes the body change from its resting parasympathetic state to its aroused sympathetic state
ADRENALINE -
the stress hormone adrenaline is released from the adrenal gland into the bloodstream, this triggers physiological changes in the body which creates the physiological arousal necessary for the fight or flight response
IMMEDIATE AND AUTOMATIC -
all of this happens in an instant as soon as the threat is detected, this is an acute response and an autonomic reaction in the body
PARASYMPATHETIC ACTION -
finally once the threat has passed, the parasympathetic system returns the body to its resting state, it works in opposition to the sympathetic system
THE STRUCTURE AND FUNCTION OF NEURONES -
there are 100 billion neurones in the human nervous system, 80% of these are located in the brain, by transmitting signals electrically and chemically, these neurons provide the nervous system with its primary means of communication
TYPES OF NEURONES -
there are three types of neurones, all with different variations in their structure and function, they are:
sensory neurones
relay neurones
motor neurones
THE STRUCTURE OF NEURONES -
they vary in size from less than a millimetre, to up to a meter long, but they all share the same basic structure
the cell body includes a nucleus, which contains the genetic material of the cell
branch like structures called dendrites protrude from the cell body to carry nerve impulses from near by neurones towards the body
the axon is covered in a fatty layer that protects the axon and speeds up transmission of the impulse
the myelin sheath has segmented gaps called nodes of Ranvier, these speed up transmission by forcing the impulse to jump across the gaps along the axon
finally at the end of the axon are terminal buttons that communicate with the next neurone in the chain across a gap known as the synapse
LOCATION OF NEURONES -
the cell bodies of motor neurones may be in the central nervous system (CNS) but they have long axons which form part of the PNS
sensory neurones are located outside of the CNS, in the PNS in clusters known as ganglia
relay neurones makeup 97% of all neurones and most are found within the brain and visual system
ELECTRICAL TRANSMISSION -
when a neurone is in a resting state, the inside of the cell is negatively charged compared to the outside, when a neurone is activated by a stimulus, the inside of the cell becomes positively charged for a small period of time causing an action potential to occur, this creates an electrical impulse that travels down the axon towards the end of the neurone
SYNAPTIC TRANSMISSION -
CHEMICAL TRANSMISSION -
neurons communicate with each other within groups known as neural networks
each neuron is separated by an extremely tiny gap called a synapse
signals are transmitted electrically in neurones, but chemically across synapses
when the electrical impulse reaches the end of a neurone (presynaptic terminal) it triggers the release of neurotransmitters from tiny sacs called synaptic vesicles
NEUROTRANSMITTERS -
neurotransmitters are chemicals that diffuse across the synapse to the next neuron in the chain, once a neurotransmitter crosses the gap, its taken up by a postsynaptic receptor site on the dendrite of the next neuron
here the chemical signal is transferred back into an electrical impulse and the process of transmission begins again in this other neuron
the direction of transmission can only be one way and only specific neurotransmitters will have a receptor site on certain neurons
when a specific number of postsynaptic receptor sites are full, the next neuron will then fire, the neurotransmitters then release and are either broken down or reabsorbed back into the presynaptic terminal
EXCITATION AND INHIBITION -
neurotransmitters wither have an inhibitory or excitatory effect on the neighbouring neurons
for example the neurotransmitter serotonin causes inhibition in the receiving neuron, resulting in the neuron becoming more negatively charged and less likely to fire
in contrast noradrenaline causes an excitation of the postsynaptic neuron by increasing the positive charge, making it more likely to fire
SUMMATION -
whether a postsynaptic neuron fires is decided by the process of summation, the excitatory and inhibitory effects are summed
if the net results inhibitory, the neuron wont fire, if its excitatory it will
therefore the action potential of the neuron is only triggered if the sum of the excitatory and inhibitory signals at any one time reaches the threshold
LOCALISATION OF FUNCTION IN THE BRAIN -
LOCALISATION VS HOLISTIC THEORY -
during the 19th century, scientists such as broca and wernicke discovered that specific areas of the brain are associated with particular physical and physiological functions
before these investigations, scientists generally supported the view that the brain works holistically (all parts of the brain worked together to perform all cognitive functions)
in contract broca and wernicke argued that the brain worked in a localised way, the idea that different parts of the brain perform different functions and are involved with different part of the body
it also suggests that if a certain brain area becomes damaged, the function associated with that area will also be affected
HEMISPHERES OF THE BRAIN -
the main part of the brain is split into two symmetrical left and right hemispheres
some of our physical and physiological functions are controlled or dominated by a particular hemisphere, this is called lateralisation for example, language is linked with the left hemisphere
as a general rule, activity on the left hand side of the body is controlled by the right hemisphere, and visa versa for the right hand side
THE MOTOR, SOMATOSENSORY, VISUAL AND AUDITORY CENTRES -
the cortex of both hemispheres are subdivided into four lobes, they are called the:
frontal lobe
parietal lobe
temporal lobe
occipital lobe
each lobe in the brain is linked with different functions
at the back of the frontal lobe is the motor area which controls voluntary movement in the opposite side of the body
at the front of the parietal lobes is the somatosensory cortex, that separated by the central sulcus, this is where sensory information from the skin is represented, the amount of somatosensory area devoted to a body part denotes its sensitivity
in the occipital lobe at the back of the brain is the visual area, each eye sends information from the left visual field to the right visual cortex, and information from the right visual field to the left visual cortex
the temporal lobes house the auditory area which analyses speech based information
THE LANGUAGE CENTRE OF THE BRAIN -
unlike the areas found in both hemispheres, language is restricted to the left side of the brain in most people
in the 1880s broca identified a small area in the left frontal lobe responsible for speech production
damage to broca’s area causes brocas aphasia which is characterised by slow, labourus and influent speech
wernicke was describing people who had no problem speaking, but had difficulty understanding it (could speak fluently, but it was meaningless to them)
wernicke identifies a region in the left temporal lobe as being responsible for language understanding, damage to this area results in wernickes aphasia, people who have it will often produce nonsense words as part of the content of their speech
EVALUATION POINTS -
EVIDENCE FROM NEUROSURGERY -
one strength of the localisation theory is that damage to areas of the brain has been linked to mental disorders
neurosurgery is a last resort method for treating some mental disorders, targeting specific areas of the brain which may be involved
for example a report on a surgery to isolate a region of the brain linked to OCD showed that out of 44 people who had the surgery, 30% had met the criteria for a successful surgery and 14% had partially met the criteria
this success of these procedures suggests that behaviours associated with serious mental disorders may be localised
EVIDENCE FROM BRAIN SCANS -
another strength is evidence from brain scans that supports the idea that many everyday brain functions are localised
for instance, Petersen et al (1988) used brain scans to demonstrate how wernickes area was active during a listening task and brocas area was active in a reading task
also a review of long term memory studies by Buckner and Petersen revealed that semantic and episodic memories reside in in different parts of the prefrontal cortex
these studies confirm localised areas for everyday behaviours
therefore objective methods of study for measuring brain activity have provided scientific evidence that many brain functions are localised
LANGUAGE LOCALISATIONS QUESTIONED -
one limitation is that language may not be localised to just brocas and wernickes areas
a review by dick and tremblay (2016) found that only 2%of modern researchers think that language in the brain is completely controlled by broca and wernickes areas
advances in brain imaging techniques, such as fMRI mean that neural processes in the brain can be studied clearer than before, these show that language function is distributed far more holistically than it was originally thought before, as ‘language streams’ have been identified across the cortex, including in areas of the right hemisphere
this suggests that rather than being confined to a few key areas, language may be organised more holistically in the brain, which contradicts the localisation theory
HEMISPHERIC LATERALISATION AND SPLIT BRAIN RESEARCH -
LOCALISATION AND LATERALISATION -
localisation refers to the fact that some functions such as vision and language are governed by very specific areas in the brain
lateralisation refers to the fact that the brain has two hemispheres, for some functions, the localised areas appear in both hemispheres EG the visual cortex appears in both the left and right hemispheres
LEFT AND RIGHT HEMISPHERES -
in the case of language, the two main centres are only in the left hemisphere for most people, brocas area is in the left frontal lobe and wernickes area is in the left temporal lobe, so we can say language is lateralised as its performed by one hemisphere rather than the other
the right hemisphere can only produce rudimentary words and phrases but does contribute emotional context to what is being said, so it can be said the LH is the analyser and the RH is the synthesiser
many functions are not lateralised, for example vison, motor and somatosensory areas appear in both hemispheres
but the brain works in a contralateral wiring way, meaning movement in the left side of the body is controlled by the right hemisphere, and the left hemisphere controls movement in the right side of the body
for vision, the function is contralaterally and ipsilaterally wired, as each eye has a left and right visual field, both LVFs send information to the right hemisphere and both RVFs send information to the left hemisphere
this allows the visual areas to compare the slightly different perspectives from each eye to aid depth perception
SPLIT BRAIN RESEARCH -
a ‘split brain’ operation involves severing connections between the right and left hemispheres, it was thought to reduce epilepsy by stopping the excessive electrical activity between the hemispheres in an epileptic fit
by cutting the connections, split brain studies could happen to investigate how the hemispheres function when they cant communicate with each other
SPERRYS RESEARCH -
Sperry (1968) devised a program to study how two separated hemispheres deal with, for example speech or vison
PROCEDURE -
eleven people who had split brain operations were studies using a special set up in which an image would be projected to a participants RVF (processed by the LH) and the same or different image would be projected into the LVF (processed by the RH)
in a normal brain the corpus callosum would immediately share the information between both hemispheres to give a complete picture of the visual world
however presenting the image to one hemisphere of a split brain patient means that the information cannot be conveyed from one hemisphere to the other
FINDINGS -
when a picture of an object was shown to a participants RVF (linked to LH), the participant could describe what they had seen
but they could not do this if the object was shown in the LVF and relayed to the RH - they would say nothings there, this is because in the connected brain, messages from the right hemisphere are relayed to the language centres in the left hemisphere, but this is not possible in the split-brain patients
although participants could not give verbal labels to objects projected in the LVF, they could select a matching object out of sight using their left hand as its linked to the right hemisphere that controls the the side of the body
the left hand was also able to select an object that was most closely associated with an object presented to the LVF (EG selecting an ash tray when shown a cigarette)
if a pinup picture was shown to the LVF there was an emotional reaction (EG a giggle) but the participants usually reported seeing nothing or just a flash of light
CONCLUSIONS -
these observations show how certain functions in the brain are lateralised in the brain and support the view that the LH is verbal and the RH is silent but emotional
EVALUATION POINTS -
LATERALISATION -
LATERALISATION IN THE CONNECTED BRAIN -
one strength is research showing that even in connected brains, the two hemispheres process information differently
for example Fink et al (1996) used PET scans to identify which brain areas were active during a visual processing task
when participants with connected brains were asked to attend to global elements of an image, regions in the RH were much more active, but when asked to focus on the finer details, the specific areas of the LH tended to dominate
this suggests that, at least as far as visual processing is concerned, hemispheric lateralisation is a feature of the connected brain as well as the split brain
ONE BRAIN -
one limitation is the idea that the LH as the analyser and the RH as the synthesiser may be wrong
there may be different functions in the two hemispheres, but research suggests that people do not have a dominant hemisphere which create a different personality
Nielsen et al (2013) analysed brain scans of over 1000 people aged 7 to 29 years old and did find people used one side of their brain more for certain tasks, but no evidence to suggest there is a dominant side (EG no artists brain or mathematicians brain)
this suggests that the notion of left or right brained people is wrong
SPLIT BRAIN RESEARCH -
RESEARCH SUPPORT -
one strength is support from more recent split brain research
this study showed that split brain participants actually perform better than connected controls on certain tasks, for example they were faster at identifying odd ones out in an array of similar items than controls
in the normal brain, the LHs better cognitive strategies are watered down by the RH
this supports sperrys earlier findings that the left brain and right brain are distinct
GENERALISATION ISSUES -
one limitation of sperrys research is that causal relationships are hard to establish
the behaviour of sperrys split brain patients was compared to a neurotypical group, an issue though is that non of the control group had epilepsy, which is a major confounding variable
this means that some of the unique features of the split brain participants cognitive abilities might have been due to their epilepsy and not their split brain operation