Cerebral Cortex Flashcards
What are grey and white matter?
Grey matter – there are around 50bn neurones and 500bn glial cells and only 30% is visible as 70% is hidden in the sulci
White matter - includes myelinated neuronal axons forming white matter tracts
What are the different fibres in white matter?
- Association fibres:
- Connect areas within the same hemisphere - Commissural fibres:
- Connect left -> right hemisphere e.g corpus calossum - Projection fibres:
- Connects cortex -> lower brain structures.
e. g Thalamus, brain stem and spinal cord.
What are the cortical layers in the grey matter?
Layer 1 – contains mainly neuropil (dense network of interwoven nerve fibres and glia)
Layers 2/3 – contains pyramidal neurones that have primary Cortico-cortical connections
*layers 1-3 mainly cortico-cortical connection (association)
Layer 4 - has mainly stellate neurones with local axons in the primary sensory cortices that receive input from the thalamus
Layers 5/6 - (projection neurons) typically contain pyramidal neurones whose axons leave the cortex (there are about 50 distinct cortical regions)
- Contains the large Betz cells
** also arranged in columns - more dense vertical connections, basis for topographical organisation - neurons with similar properties connected in same column
What are the functions of the lobes of the brainr?
occipital - vision association cortex
- Ventral pathway – form and colour
- Dorsal pathway – spatial relationships and movement
Parietal - spatial map of body in the surroundings
- Injury may cause disorientation and the inability to read a map or understand spatial relationships – i.e. apraxia and neglect
Temporal – language, object recognition, memory and emotion.
- Injury leads to agnosia (inability to interpret sensations) and receptive aphasia (inability to create speech)
Frontal – judgement, foresight, personality and appreciation of self in relation to world
- Injury leads to deficits in planning and inappropriate behaviour.
What would lesions in the primary motor cortex cause?
Paralysis – full or partial loss of fine voluntary movements contralateral
Paresis – muscular weakness
What would lesions in the pre motor cortex/ motor association area cause?
Apraxia – difficulty in motor planning to perform voluntary tasks
What would lesions in the pre- frontal association area cause?
- Deficits in planning and inappropriate behaviour.
> This area is often involved in – personality, self-control, attention, planning, emotions, motivation, decision making and reasoning. - Aphasia – inability to crate speech but preserved comprehension.
> Broca’s area is in the frontal lobe.
What would lesions in the parietal cortex cause?
Primary somatosensory cortex:
- Sensory deficits – in perception of basic sensory information
Sensory association area:
- Sensory deficits – in interpretation of sensory information e.g spatial neglect – unawareness of contralateral side
- Area is involved in – tactile recognition, flavour recognition, spatial orientation, ability to read maps, reading, writing and calculations
> Alexia – inability to recognise or read words
> Agraphia – inability to write words
> Acalculia – inability to perform calculations
What would lesions in the temporal cortex cause?
Primary auditory cortex:
- Deafness.
Auditory association area:
- Visual deficits – in interpreting auditory information.
> Wernicke’s/receptive aphasia – impaired comprehension but preserved speech function
Temporal lobe:
- Anterograde amnesia – inability to form new memories
What would lesions in the occipital lobe cause?
Primary visual cortex:
- Blindness.
Visual association area:
- Visual deficits – in interpreting visual information
> Prosopagnosia – inability to recognise familiar faces
What is hemispheric specialisation?
One or the other hemisphere is more active during certain tasks:
- e.g language is dominant in the left side – this does not mean the other hemisphere is not working
Left is more verbal and analytical
Right is more non-verbal
Corpus callosum has been cut
- See “FACE” on the right and they can say face as the verbal is on the same side as the contralateral recognition of sight.
- See “FACE” on the left and they can only draw a face and not say it
How can you test brain function by stimulation?
Transcranial Magnetic Stimulation (TMS)
Measures the effects if interference with normal information processing due to electro-magnetic stimulation of neurones
Benefits over lesion/patient studies:
- Effects of stimulation are generally more precise
- Healthy participants can be used as their own control – as they have a lesion that can be on/off
- Insufficient time for functional reorganisation to take place so recovery processes of the brain are unlikely to confound the results
- investigation of temporal dynamics of on-line neuronal processing
How can TDCS be used to test brain function?
transcranial direct current stimulation
changes the local excitability of neurons, increasing or decreasing the firing rate
How can PET be used to test brain function?
Positron Emission Tomography
measures changes in amount flow directly to a brain region
Uses a radioactive tracer attached to a molecule to locate brain areas where that molecule is being absorbed in the brain
Expensive
How can fMRI be used to test brain function?
measures changes in amount of blood oxygen in a brain region
presumed to be due to increased electrical activity in that area
