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Structure of the Nervous System (Cortical Columns (Mountcastle (Recorded…
Structure of the Nervous System
Levels of organisation
Cerebral Cortex
Divided into
4 lobes:
Frontal, Parietal, Temporal and Occipital
Divided into zones based on:
Gross anatomy, variations of cellular properties, connectional anatomy & functional properties
Communicating areas should perform similar functions
A lot of variation between people for each area
Frontal Lobes
Central Sulcus & Prefrontal Sulcus divides the frontal & parietal lobes
Motor striate controls body movement
Severe reduction in grey matter levels as you age
Gogtay
Higher order association cortices mature only after lower-order somatosensory and visual cortices
Behaviour comes from the brain's anatomy - understanding its organisation allows us to understand behaviour
Neural Networks
Nervous system consists of NN that integrate and distribute information
Simplest NN can be represented as a
chain of connected neurones
E.g. knee jerk arc or cells connecting retinal receptors of the visual cortex
Cortical neuron -> thalamic neuron (both brain) -> optic nerve ->bipolar cell -> retina (eye)
Convergence
Info from
several neurones
is integrated to influence the firing of
a few
Divergence
Info from a few neurones is distributed to several other neurones
Networks are organised
hierarchically
- info is passed from one place to the next and is transformed as it crosses various points
Cortical Networks
Input =
Association Fibre
Association fibres connect areas of the brain but they DO NOT cross hemispheres
Layer 3 input from other brain areas
No inputs in layers 1,2,5&6
Cortical Columns
Mountcastle
Recorded the firing properties of neurones
Moved the recording electrode to the surface and the firing properties changed
Hubel & Wiesel
Recorded from PVC mapping inputs from each eye & looking for neurones with 'ocular dominance'
Ocular dominance columns are organised into stripes - unique patterns in everyone
In many regions of the cerebral cortex, neurones are organised into
columnar modules = information processing units
Vertical because neurones from above and below form dense connections and fewer connections with neurones in some layers
Around 110 neurones in each column
Human cerebral cortex has 1 million cordial columns
Orientation Columns
PVC neurones have columns that respond specifically to visual stimuli
Cytoarchitecture
The properties of the layers change from one part of the cortex to the other
Cellular properties vary - reflects the variability in the way information is processed in these zones
3 main zones in the frontal lobes are distinguished on the basis of cytoarchitecture - no gross landmark to divide them
Connectional Anatomy
Cortical zones are connected to each other and subcortical areas in specific ways - E.g. frontal lobe connections of the motor system
PFC -> Premotor cortex -> primary motor cortex -> spine -> muscles
The cerebellum & basal ganglia modulate activity in each cortical area through independent 'looped' connections
Each level of frontal lobe exchanges info with the cerebellum and basal ganglia - monitor and modify activity in each level
Cerebral Cortex
= The outer surface of the forebrain that covers the other forebrain structures
6 Layers:
Molecular layer
External granular layer
External pyramidal layer
Internal granular layer
Internal pyramidal layer
Polymorphical layer