Organisation of Cerebral Cortex Flashcards
Grey Matter?
Neurons (50bn) Glial cells (500bn)
30% is visible
70% is hidden in the SULCI
White Matter?
Includes
o myelinated neuronal axons
which go on to form white matter tracts
3 types of White Matter fibres?
- Association fibres
o connect areas within the same hemisphere - Commissural fibres
o connect left hemisphere to right hemisphere - Projection fibres
o connect cortex with lower brain structures (e.g. thalamus), brainstem and spinal cord
What is the neocortex?
A new evolutional development that describes the 6 layers in the diagram!
a part of the cerebral cortex concerned with sight and hearing in mammals, regarded as the most recently evolved part of the cortex
ONENOTE!
How many Cortical layers are there in the Grey Matter?
6!
Layer 1 of the Grey Matter?
Contains mainly o neuropil (dense network of interwoven nerve fibres & glia)
Layer 2/3 of the Grey Matter?
Contains
o pyramidal neurons that have primary Cortico-cortical connections
Layer 4 of the Grey Matter?
Has mainly
o stellate neurones
o with local axons in the primary sensory cortices
o that RECEIVE input from the thalamus
Layer 5/6 of the Grey Matter?
Typically contain
o pyramidal neurons
o whose axons leave the cortex (there are about 50 distinct cortical regions)
- contains the large BETZ CELLS
Output/Inputs of the cortical layers of the Grey Matter?
Layer 1/2/3 = Output to CORTEX
Layer 4 = INPUT
Layer 5/6 = Output to NON-CORTEX
How are the neurones organised locally in the cortical layers?
Into COLUMNS
o along the columns, have dense vertical connections
o these neurones interact with one another
o basis for TOPOGRAPHICAL ORGANISATION
Brodmann’s Areas?
Split the cerebral cortex up into areas with distinct histological patterns & functions
i.e. (respond to same stimuli)
Explain the Association Fibres
WHITE MATTER
2 TYPES
o Short Association Fibres - connect SHORT distances
o Long Association Fibres = connect more DISTANT structure
LUDLEYS!!
Long Association Fibres?
White Matter - connect more distant structures
e.g.
o Super Longitudinal Fasciculus
- connects frontal & occipital lobes
o Arcuate Fasciculus
- connects frontal & temporal lobes
o Inferior Longitudinal Fasciculus
- connects temporal & occipital lobes
o Uncinate Fasciculus
- connects anterior frontal & temporal lobes
Function of Commissural and Projection Fibres?
WHITE MATTER
Commissural Fibres
o connect hemispheres e.g. corpus callosum
Projection Fibres
o long projections out of cortex e.g. internal capsule
Neocortex is comprised of different lobes - what are these lobes?
Frontal Lobe
Parietal Lobe
Occipital Lobe
Temporal Lobe
Occipital Lobe?
Vision Association Cortex
o Ventral pathway = form & colour
o Dorsal pathway = spatial relationships * movement
Parietal Lobe?
Posterior Parietal Association Cortex
o Spatial map of the body in the surroundings
Injury may cause
o disorientation
o inability to read a map
o inability to understand spatial relationships e.g. apraxia & neglect
Temporal Lobe?
Language, object recognition, memory & emotion
Injury leads to o Agnosia (inability to interpret sensations although sense organs & nerves are functioning normally)
o Receptive aphasia (inability to create speech)
Frontal Lobe?
Judgement, foresight, personality and appreciation of self in relation to the world
Injury leads to
o deficits in planning
o inappropriate behaviour
Primary Cortices?
Predictable function
Organised topographically
Left-right symmetry
Association Cortices?
Function less predictable
Not organised topographically
Left-right symmetry weak/absent
What helps in ‘Voluntary skeletal muscle movements’?
o Primary motor cortex
- precentral gyrus
o Premotor cortex
- motor association area
What helps in ‘Recognition & interpretation of sensory information from skin, muscles and taste buds’?
o Primary somatosensory cortex
- postcentral gyrus
o Sensory association area
BOTH = Parietal Lobe
What helps in ‘Vision’?
Visual Association Area
Primary Visual Cortex
BOTH = Occipital Lobe
What helps in ‘Hearing’?
Auditory Association Area
Primary Auditory Cortex
BOTH = Temporal Lobe
What helps in ‘Coordinate information from other association areas’?
Prefrontal Association Area
= Frontal Lobe
Lesion in posterior part of brain (Onenote!)?
Primary Motor Cortex
o Paralysis
- full or partial loss of fine voluntary movements contralateral
o Paresis
- muscular weakeness
Pre-motor cortex/Motor association cortex
o Apraxia
- difficulty in motor planning to perform voluntary tasks
Lesion in Frontal Lobe?
Prefrontal Association Area
o Deficits in planning & inappropriate behaviour
- due to what the area controls!
o Aphasia
- inability to create speech but preserved comprehension
- BROCA’S AREA is in the frontal lobe!!
Lesion in Parietal Lobe?
Primary Somatosensory Cortex
o Sensory deficits - in PERCEPTION of basic sensory information
Sensory Association Area
o Sensory deficits - in INTERPRETATION of sensory information
- e.g. Spatial neglect (unaware of contralateral side)
- Area involved in tactile recognition, flavour recognition, spatial orientation, ability to read maps, reading, writing and calculations
SO
Can have
o Alexia - inability to recognise/read words
o Agraphia - inability to write words
o Acaluclia - inability to perform calculations
Lesions in Occipitial Lobe?
Primary Visual Cortex
o Blindness
Visual Association Cortex
o Visual deficits - in interpretation of visual info.
e.g. PROSOPAGNOSIA - inability to recognise familiar faces
Lesions in Temporal Lobe?
Primary Auditory Cortex
o Deafness
Auditory Association Cortex
o Visual deficits - in interpretation of auditory info.
e.g. Wernicke’s/receptive aphasia - impaired comprehension but preserved speech function
Temporal Lobe
o Anterograde amnesia - inability to form NEW memories
Functional methods available to test functionality of the different parts of the brain?
TMS (Transcranial Magnetic Stimulation) PET fMRI EEG MEG Structural Imaging (DTI)
How is TMS used to test lesions?
Transcranial Magentic Stimulation
Measures the effects if interference with normal info. processing due to electro-magnetic stimulation of neurones
Benefits of using TMS?
o Effects of stimulation generally more precise
o Healthy ppts. can be used as control
o Insufficient time for functional reorganisation to take place so recovery processes of the brain unlikely to confound results
o Allows investigation of temporal dynamics of on-line neuronal processing
How is PET used to test lesions?
Positron Emission Tomography
Measures changes in amount of flow directly to a brain region
o use radioactive tracer attached to a molecule which is absorbed in brain
Limitations of PET?
£££
How is fMRI used to test lesions?
Measures changes in amount of blood O2 in a brain region
How is EEG used to test lesions?
Electroencephalography
Measured ELECTRICAL SIGNALS generated by the brain
How is MEG used to test lesions?
Magnetoencephalography
Measured MAGNETIC FIELDS generated by the electrical currents in the brain
How is Structural Imaging used to test lesions?
Measures effects of lesions in white matter
o DTI - diffusion tensor imaging
- (movement of water molecules in brain can be used to infer underlying structure of the white matter which can estimate connections)
Traumatic brain injury
o thought to be due to disruptions in these white matter tracts
Hemispheric Specialisation?
One or the other hemisphere is more active during certain tasks
e.g. language dominant in L-SIDE
Left Hemisphere?
Verbal + Analytical
Logical + Scientific
Right Hemisphere?
Non-Verbal!
Artistic + Creative
Callosotomy?
Pallative surgical procedure for treatment of seizures
o remove corpus callosum as key for the interhemispheric spread of epileptic activity
Callosotomy and seeing the hemispheres?
Can show things to one eye or another and see that the image is being processed by ONE HEMISPHERE
e.g.
o If show the L-hemisphere (flashes on right field of view), will be able to READ
o If show the R-hemisphere (flashes on left field of view), will be able to DRAW but NOT read
