biopsychology

• the nervous system: a specialised network of cells in the human body and is our primary internal communication system. it has two main functions:

  1. to collect, process and respond to information from the environment
  2. to co-ordinate the working of different organs and cells in the body

  it is divided into two sub-systems

  1. central nervous system
  2. peripheral nervous system
• the central nervous system:

  • made up of the brain and spinal cord

  brain = the centre of all conscious awareness, the brains outer layer (cerebral cortex) is highly developed in humans. the brain is divided into 2 hemispheres.

  spinal cord = extension of the brain. responsible for reflex actions

  • passes messages to and from the brain and connects nerves to the PNS
• the peripheral nervous system:

  transmits messages via millions of neurons to and from the CNS. the PNS is further sub-divided into the:

  • autonomic nervous system (ANS) which governs vital functions into the body such as breathing, heart rate, sexual arousal and stress responses
  • somatic nervous system (SNS) controls muscle movement and receives information from sensory receptors
• the endocrine system: glands and hormones

  • acts more slower than the nervous system but has powerful effects
  • various glands in the body such as thyroid gland produce hormones
  • hormones are secreted into the bloodstream and affect any cell in the body that has a receptor for a particular hormone
  • the thyroid gland produces the hormone thyroxine which affects cells in the heart (increases heart rate) it also affects cells throughout the body increasing metabolic rates which affects growth rates
• the endocrine system: glands and hormones

  • the major endocrine gland is the pituitary gland which is located in the brain
  • it is often called the master gland because it controls the release of hormones from all the other endocrine glands in the body
• the endocrine system: fight or flight

  • the endocrine system and the ANS work together e.g. during a stressful event
  • when a stressor is received the first thing that happens is the hypothalamus triggers activity in the sympathetic branch of the ANS
  • the ANS changes from its resting state (parasympathetic state) to the psychologically aroused state (sympathetic state)
  • the stress hormone adrenaline is released from the adrenal medulla into the bloodstream
  • adrenaline triggers psychological changes in the body e.g. increased heart rate which creates the arousal fight or flight response
• the endocrine system: fight or flight response

  • the psychological changes include increased heart and breathing rate, dilated pupils and saliva production
  • once the threat has passed the parasympathetic branch of the ANS works in opposition to the sympathetic nervous system
  • the parasympathetic system acts as a brake and reduces the activities in the body that were increased by the actions of the sympathetic branch ( rest and digest response)
• structure and function of neurons:

  • there are 100 billion neurons in the human nervous system
  • 80% of them located in the brain
  • by transmitting signals electrically and chemically they provide the nervous system with primary needs of communication
• sensory neuron = carry messages from the PNS to the CNS. they have long dendrites and short axons
• relay neurons = they connect sensory neurons to the motor or other relay neurons. they have short dendrites and short axons
• motor neurons = these connect the CNS to effectors such as muscles and glands. they have short dendrites and long axons
• the structure of a neuron:

  • the cell body includes a nucleus which contains genetic material of the cell, branch like structures called dendrites produce from the cell body. these carry nerve impulses from neurons to the cell body
  • the axon carries impulses away from the cell body down the neuron, the axon is covered in a fatty layer called the myelin sheath that protects the axon and speeds up electrical transmission of impulses
• the structure of a neuron:

  • the myelin sheath is segmented by gaps called nodes of ranvier. these speed up the transmission of impulses by forcing it to jump across the gaps along the axon
  • at the end of the axon is terminal buttons that communicate with the next neuron across the gap known as a synapse
• electrical transmission - the firing of a neuron

  • when a neuron is in a resting state the inside of the cell is negatively charged compared to the outside
  • when a neuron is activated by a stimulus the inside of the cell becomes positively charged for a split second causing action potential to occur
  • this creates an electrical impulse that travels down the axon towards the end of the neuron
• synaptic transmission: chemical transmission synapses

  • neurons communicate with each other in groups known as neural networks
  • each neuron is separated from the next by a synapse
  • the synapse includes spaces between them (synaptic cleft) as well as the presynaptic terminal and postsynaptic receptor site
  • signals within neurons are transmitted electrically however signals between neurons are transmitted chemically by synaptic transmission
  • when the electrical impulse reaches the end of the neuron it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles
• synaptic transmission: neurotransmitters

  • chemicals that diffuse across the synapse to the next neuron in the chain
  • once the neurotransmitter crosses the gap it is taken up by the postsynaptic receptor sites where the chemical message is converted back into an electrical impulse and the process of the transmission begins again in another neuron
  • each neurotransmitter has its own specific molecular structure that fits perfectly into a post-synaptic receptor site (lock and key method)
  • neurotransmitters also have specialist functions
• excitation and inhibition:

  • the neurotransmitter serotonin causes inhibition in the receiving neuron resulting in a negative charge meaning it is less likely to fire
  • in contrast adrenaline causes excitation of the postsynaptic neuron by increasing its positive charge and making it more likely to fire
• summation:

  • the question whether a postsynaptic neuron does fire is decided by the process of summation
  • if the net effect on the postsynaptic neuron is inhibitory then the neuron is less likely to fire if the net effect is excitatory it is more likely to fire
  • the inside of the neuron then becomes positively charged and once the electrical impulse is created it travels down the neuron
  • therefore action potential of the neuron is only triggered if the sum of excitatory or inhibitory signals at one time reaches the threshold
• localisation of function in the brain: holistic theory

  • scientists such as Broca and Wernicke discovered that specific areas of the brain are associated with particular physical and psychological functions
  • before these scientists supported the holistic theory that all parts of the brain were involved in processing thought and action
  • Broca's and Wernicke's idea is that different parts perform different tasks involved in the body which then follows if a certain area of the brain becomes damaged through illness or injury the function associated with that area will also be affected
• hemispheres of the brain and the cerebral cortex:

  • the brain is divided into 2 symmetrical halves called the left and right hemispheres
  • some of our physical and psychological functions are controlled by a particular hemisphere
  • activity on the left side of the body is controlled by the right hemisphere and activity on the right side is controlled by the left hemisphere
  • the outer layer of both hemispheres is the cerebral cortex like a tea cosy covering the inner parts of the brain
  • it is 3 mm thick and it separates us from others because the cortex is more developed
• cerebral cortex = appears grey due to the location of cell bodies hence the phrase 'grey matter' to describe the surface of appearance of the brain
• the motor, somatosensory, visual and auditory centres:

  • at the back of the frontal lobe in both hemispheres is the motor area which controls voluntary movement in the opposite side of the body. damage to this area may result in loss of control over fine movements
  • at the front of both parietal lobes is the somatosensory area which is separated from the motor by the central sulcus. it is where sensory info from skin e.g. touch, pressure, is represented. the amount of the area devoted to a particular body part demotes its sensitivity
• the motor, somatosensory, visual and auditory centres:

  • in the occipital lobe at the back of the brain is the visual area. each eye sends info from the right visual field to the left cortex and the left visual field to the right cortex. this means damage to the left hemisphere can produce blindness in part of the right visual field
  • the temporal lobes house the auditory area which analyses speech based info. damage may produce partial hearing loss depending on the damage can be worse. damage to the Wernicke's area may affect the ability to comprehend language
• the language area of the brain:

  • Broca identified that a small area in the left frontal lobe is responsible for speech production. damage to this area causes Broca's aphasia which is characterised by speech that is slow and lacking in fluency
  • around the same time, Wernicke identified a region in the left temporal lobe as being responsible for language comprehension which would result in Wernicke's aphasia which is where people will produce nonsense words as part of content in their speech
• A03 localisation of brain function:

  + brain scan evidence of localisation

  • Petersen et al used brain scans to demonstrate how Wernicke's area was active during a listening task and Broca's area was active during a reading task suggesting areas of the brain have different functions
  • Tulving et al study of LTM revealed that semantic and episodic memory reside in different parts of the prefrontal cortex
  • there are many objective methods measuring brain activity which provides scientific evidence for localisation in the brain
• A03 localisation of brain function:

  +neurosurgical evidence

  • in the 1950s surgery's involved connections in the frontal lobe in attempt to control aggressive behaviour
  • neurosurgery is still used today in extreme cases of OCD and depression
• A03 localisation of brain function:

  + case study evidence

  • Phineas gage worked on a railway line where a pole went through his left cheek into his skull into the most of his left frontal lobe
  • gage survived but the damage to his brain left a mark on his personality where he turned from someone calm and reserved to quick tempered and rude
  • this is significant evidence as it suggests the frontal lobe may be responsible for regulating mood
• plasticity and functional recovery:

  brain plasticity

  • the brain is 'plastic' as it has the ability to change throughout life
  • during infancy, the brain experiences a rapid growth of synaptic connections peaking at 15,000 per neuron at the age 2-3
  • synaptic pruning = rarely used connections are deleted and frequently used connections are strengthened
  • recent research has suggested that at any in life existing neural connections can change or new ones can be formed through learning and experience
• plasticity and functional recovery:

  research:

  • Maguire studied the brains of London taxi drivers and found significantly more volume of grey matter in the posterior hippocampus than in a matched control group
  • this part of the brain is associated with development of spatial +navigational skills
  • as part of taxi driver training the have to take a knowledge test which assesses recall of city streets and possible routes, it appears the result of learning this experience is to alter the structure of their brains
  • the longer they were in the job, the more pronounced the structural difference
• functional recovery of the brain after trauma:

  • following physical injury or other forms of trauma unaffected areas of the brain are often able to adapt and compensate for those damaged areas
  • the functional recovery which may occur after trauma is another example of neural plasticity
  • healthy brain areas may overtake the damaged or missing ones
  • neuroscientists suggest that the process can come quickly after trauma then slow down after weeks or months
  • the individual then may require rehabilitative therapy for further recovery
• what happens in the brain during recovery:

  • the brain is able to rewire and reorganise itself by forming new synaptic connections close to the area of damage
  • secondary neural pathways that wouldn't really be used to carry out functions are 'unmasked' to enable functioning to continue
• the process of structural changes:

  1. axonal sprouting = the growth of a new nerve endings which connect with other undamaged nerve cells to form new neural pathways
  2. reformation of blood vessels
  3. recruitment of similar areas on opposite side of the brain to perform specific tasks e.g. Broca's area, if the left side was damaged the right side would carry out its functions
• A03 plasticity and functional recovery:

  -practical application

  • contributed to neurorehabilitation
  • following injury or illness to the brain, spontaneous recovery tends to slow down after a number of weeks so physical therapy may be required to maintain improvements in functioning
  • techniques may include movement therapy and electrical stimulation of the brain to counter deficits in motor or cognitive functioning
  • this shows although the brain may 'fit itself' to a point the process requires further intervention to be fully successful
• A03 plasticity and functional recovery:

  -negative plasticity

  • the brains ability to rewire itself can have maladaptive behavioural consequences
  • e.g. prolonged drug use has been shown to result in poor cognitive functioning as well as increased risk of dementia in later life and 60-80% have experienced phantom limb syndrome experiencing limb sensations
  • these sensations are usually unpleasant, painful and are thought to be due to reorganisation in the somatosensory cortex that occurs as a result of limb loss
• A03 plasticity and functional recovery:

  + age and plasticity

  • functional plasticity tends to reduce with age, the brain has greater propensity for reorganisation in childhood as it is constantly developing to new experiences and learning
  • Bezzola demonstrated how 40hrs of golf training produced changes in the neural representation of movement in ages 40-60, using FMRI researchers observed reduced motor cortex activity in novice golfers compared to control group. this shows neural plasticity continues throughout lifespan
• split brain research into hemispheric lateralisation:

  hemispheric lateralisation:

  • language is the subject to hemispheric lateralisation
  • the specialised areas associated with language are found in one of the brain's hemispheres rather than both
  • the question whether other neural processes may be organised in this way was invested in a serious of ingenious experiments was conducted by Roger Sperry ad his colleagues which he later won a Nobel prize for
• split brain studies:

  • Sperry's studies involved a unique group of people who all had the same surgical procedure called commissurotomy in which corpus callosum and other tissues which connect the two hemispheres were cut down the middle in order to separate the 2 hemispheres and control frequent and severe epileptic seizures
  • this meant for these individuals the main communication line between the hemispheres were removed
  • this allowed Sperry to see the extent to which the 2 hemispheres were specialised for certain functions and whether the can perform a task individually without the other
• Sperry's split brain procedure:

  • an image or word would be projected into the individual's right visual field and the same or different image could be projected into the left visual field
  • in the 'normal' brain the corpus callosum would immediately share the info between the two hemispheres giving a complete image of the visual world
  • however, presenting the image to one hemisphere to a split individual patient meant that info could not be conveyed from one hemisphere to another
• Sperry's key findings:

  1. describing what you see

  • when a picture was shown to the individuals right visual field they could easily describe it however when shown to the left visual field they could not describe it or reported nothing was there

  2. recognition from touch

  • they were able to select a matching object from a grab bag of different objects using their left hand which were placed behind a screen. the left hand was also able to select the object closest associated with an object present in the left visual field
• Sperry's key findings continued:

  3. composite words

  • if two words were presented simultaneously on either side of the visual field the individual would select a key with their left hand and say the word ring. the superiority of the right hemisphere in terms of drawing tasks

  4. matching faces

  • the right hemisphere also appeared dominant in terms of recognising faces. when asked to match a face with a series of faces the picture processed by the right hemisphere was consistently selected while the left hemisphere was consistently ignored.