Organisation of the Cerebral Cortex Flashcards
What are the three types of fibre that make up white matter?
Association Fibres – connect with areas in the same hemisphere
Commissural Fibres – connect the two hemispheres
Projection Fibres – connect the cortex with lower brain structures (e.g. thalamus)
How many layers of grey matter are there?
3-6 (they are usually numbered by roman numerals)
What is the neocortex?
A part of the cerebral cortex (grey matter) concerned with sight and hearing in mammals, regarded as the most recently evolved part of the cortex
Describe the arrangement of the neocortex.
- Arranges in layers (lamina structure) and columns
- More dense ventral connections - basis for topographical organisation
- Neurons with similar properties are connected in the same column
Describe the different connections of the 6 layers of grey matter.
Layers 1-3 = mainly cortico-cortical connections
Layer 4 = input from the thalamus
Layer 5-6 = connections with subcortical, brainstem and spinal cord
What does layer 1 mainly consist of?
Neutropil – an area composed mostly of unmyelinated axons, dendrites and glial cell processes that forms a synaptically dense region containing a relatively low number of cell bodies
What type of neurone is found in layer 4?
Stellate neurones
What type of neurone is found in layer 5?
Pyramidal neurones
What are the differnet lobes of the neocortex?
- Frontal
- Parietal
- Occipital
- Temporal
Describe the organisation of the primary cortices.
Primary cortices
- function predictable
- organised topographically
- left-right symmetry
- Taste (gustatory) cortex in the inferior frontal lobe
- Smell (olfactroy) cortex in the medial temporal lobe
Describe the organisation of the association cortices.
Association cortices
- function less predictable
- not organised topographically
- left-right symmetry weak or absent
- Broca’s area in inferior frontal lobe; Wernicke’s at junction between parietal and temporal lobe
- Broca’s and Wernicke’s found on L side thus stroke on left side causes language deficits.
What are the two parts of the visual association cortex and what are they responsible for?
WHAT and WHERE pathways for analysng different attributes of visual image in different places:
Dorsal Pathway – responsible for interpretation of spatial relationships and movements
Ventral Pathway – responsible for form and colour
What is the result of lesions of the visual posterior association area(fusiform gyrus)?
- inability to recognize familiar faces
- inability to learn new faces
=a deficit called prosopagnosia (aka face blindness).
What is the role of the frontal lobe?
Executive functions e.g. planning, judgement, foresight, personality
What two areas does the prefrontal cortex receive massive inputs from?
- Sensory association cortex (somatosensory, visual and auditory)
- Dorsomedial Nucleus of the thalamus
NOTE: lesion of the dorsomedial nucleus will have similar consequences to prefrontal lobotomy
If you give someone with a unilateral parietal lobe lesion something to draw, what will you expect him or her to do?
Hemispatial neglect – they will only draw half of it
What are the consequences of a prefrontal lobotomy?
- Change in personality
- Inappropriate behaviour
- Lack of planning
- Lack of ability to remember and relate things over time
- Attention span and ability to concentrate are diminished
- Self-control is hugely impaired
What is the role of the posterior parietal association cortex?
It creates a SPATIAL MAP of the body in its surroundings from multi-modality information
What could injury of the posterior parietal association cortex lead to?
- Disorientation
- Inability to read a map or understand spatial relationships
- Apraxia
- Hemispatial neglect
Define apraxia.
Inability to make skilled movements with accuracy
What is the temporal association cortex responsible for?
- Language
- Object Recognition
- Memory
- Emotions
What are the two main consequences of injury to the temporal lobe?
AGNOSIA – inability for the brain to interpret sensory information although the nerves carrying sensory information to the brain are fine
- E.g. visual agnosia – patients can see perfectly fine but they can’t interpret sympbols such as letters
RECEPTIVE APHASIA –unable to understand language in the spoken or written forms
Who was patient HM and what was the result of his surgery?
Patient HM = bilateral ressection of anterior medial temporal lobe structures (lost most of hippocampus) to cure epilepsy.
Treated palliated seizures, but created dense anterograde amnesia –> can’t form new memories.
Describe hemispheric specialisation.
Right hemisphere = spacial perception, drawing, music.
Left hemisphere = language dominant + calculations, writing, both ears.
