Organisation of cerebral cortex Flashcards
What are the three types of fibre of the cerebral white matter?
Association fibres= connect with areas in same hemisphere
Commisural fibres= connect with two hemispheres-corpus callosum, anterior and posterioir
Projection fibres= connect the cortex with lower brain structures (e.g. thalamus), brainstem and spinal cord - cortical spinal tract
Grey matter consists of?
How is the grey matter organised?
Cell bodies
It is organised into layers (laminar structure) with 3-6 cortical layers which are designated by roman numerals with letters for laminar subdivisions (layer 1 most dorsal, layer 6 most ventral–nearest to white matter)
Layer 1-3-Mainly cortico-cortical connections
layer 1) largely acellular–some glial few neurones-mostly association fibres local connectivity
Layer 4 -Input from thalamus
Layer 5-6- Connections with subcortical, brain stem and spinal cord
5- bett cells large upper motor neurones with long projection of spinal cord and brainstem
From this slide onwards grey matter
Neocortex arrangement?
How are the neurones with similar properties locally organised into?
Layers (lamina structure) and columns
Columns
More dense vertical connections in columns are the basis for
Topographical organisation
What is the occipital cortex involved with?
Temporal lobe
Frontal lobe
Vision:
Visual cortex and Visual association cortex
Auditory cortex, auditory association area
Prefrontal association area
-Coordinates info from other association areas, controls some behaviours
What is the parietal lobe involved with?
Primary somatic sensory cortex and sensory association area
Sensory information from skin, musculoskeletal system, viscera and taste buds:
What does the posterior parietal association cortex do?
It creates a spatial map of body in its surroundings from multi-modality information
What does injury to the posterior parietal association cortex lead to?
It may cause disorientation, inability to read a map or understand spatial relationships, apraxia, hemispatial neglect
What is apraxia?
Part of brain responsible for memory
Inability to make skilled movements with accuracy
Hippocampus – in temporal
What is the temporal lobe involved with?
Language
Object recognition
Memory–hippocampus
Emotion
What does injury to the temporal lobe lead to?
Agnosia-
Receptive aphasia
What is agnosia?
-not in lecture slides
Disorder of brain whereby patient can’t interpret sensations correctly although the sense organs and nerves conducting sensation to brain function normally
Auditory- can hear but can’t interpret
Tactile- Normal sensation in hands but can’t recognise 3D objects with touch alone
Visual- See but can’t interpret symbols
What is receptive aphasia?
-not in lecture slides
Patient is unable to understand language in its spoken or written form
Hemispheric specialisation
Left hemisphere dominant
Right hemisphere dominant
Patients who have had a callosotomy -split brain have lateralised deficits in function
Left side of brain - Language dominant
Isabella
Right- Spatial processing-arty
Post callosotomy– corpus callosum
Image on right- Can verbally process cant draw
Image on left side- cant verbally explain, can draw tho
How do primary cortices and association cortices compare?
Primary cortices:
Function is predictable
Organised topographically
Left-right symmetry
Association cortices:
Less predictable
Not organised topographically
Left-right symmetry is weak or absent
How are image attributes processed?
Separately:
What (colour and form)- ventral stream- visual identification
Where (spatial relationships)- Dorsal stream- localisation
What is prosopagnosia?
Where are the lesions located
Where lesions of the visual posterior association area can result in inability to recognise faces or learn new faces but other parts are intact– face blindness
Posterior association area– fusiform gyrus
Frontal cortex function
What did frontal cortex lesions show?
judgement, foresight, personality, appreciation of self in relation to world
Characterised by lack of planning, disorganised, reduced attention span and concentration and self control hugely impaired–> inappropriate behaviour
What is a callosotomy?
Palliative surgical procedure for treatment of seizures because corpus callosum is key for interhemispheric spread of epileptic activity
How is diffusion tensor imaging- tractography used?
Movement of water molecules in brain can be used to infer underlying structure of white matter. This information is used to estimate location and connections between different white matter pathways
to measure the effect of lesions in white matter – or how these lesions might disconnect different brain areas, and lead to complex symptoms.
How does transcranial magnetic stimulation (TMS) work?
Magnetic field induces an electridc current in the cortesx, casuing neurons to fire. This can be used to test whether a specific brian area s reponsible for a funcion e.g speech
How does transcranial direct current stimulation (TDCS) work?
It changes the local excitability of neurones, increasing or decreasing the firing rate. This doesn’t directly induce neuronal firing like TMS.
What can TDCS be used to treat?
It could be used to reduce motion sickness by suppressing the area of cortex associated with processing vestibular information
How does positron emission tomography (PET) work?
Put ligand into patient and look for its binding. Diagnostic use look for dopamine metabolism –parkinsons loss of metabolism.
What is the difference between magnetoencephalography (MEG) and electroencephalography (EEG)?
MEG:
Measures magnetic fields
EEG:
Measures electric fields
What similarities are there between MEG and EEG?
Both non-invasive
MEG/ EEG measures the surface activity of the brain, but cannot directly measure the activity of interior structures.
Both noisy signals
Event related potential/evoked potentials.
Participants perform large numbers of trials then take average, as they are coarse measurements with high background.
How does functional magnetic resonance imaging work?
Measures brain activity by detecting changes associated with blood flow. This relies on fact that cerebral blood flow and neuronal activation are coupled- blood flow increases when area of brain in use
Alignment of water molecules soft tissue method of choice – ct: vascular prob acute bleed
infart- mr –spatial resolutiona dn function- activity.
How was optimism measured?
When participants imagined positive events in the future or past, the amygdala and rostral anterior cingulate cortex were more active than when they imagined negative events
Back of frontal lobe, in front of central sulcus is
Primary motor cortex–> motor association area (premotor cortex)
Skeletal muscle movement
Anterior to parietal lobe, behind central sulcus is
Primary somatic sensory cortex
Primary cortices
Location of each
Primary Motor cortex, somatic sensory cortex, visual, auditory, gustatory, olfactory
Location of each of the primary cortices
Primary motor cortex- back of frontal
Primary somatosensory cortex- anterior of parietal
Visual- Occipital
Auditory- Temporal lobe
Gustatory and olfactory less well defined
How is the grey matter organised?
It is organised into layers (laminar structure) with 3-6 cortical layers which are designated by roman numerals with letters for laminar subdivisions
What does layer 1 mainly contain?
Neuropil- area composed mostly of unmyelinated axons, dendrites and glial cell processes that form a synaptically dense region containing a relatively low number of cell bodies
What is layer 4 typically rich in?
Stellate neurones with locally ramifying axons, in the primary sensory cortices-these neurones receive input from thalamus
What do layer 5 and layer 4 to a lesser extent contain?
Pyrimidal neurones whose axons typically leave the cortex
