Problem 4 Flashcards
Histological organization of the cortex
- Neocortex
- -> 6 layers, whereas older version had 3 layers:
Paleocortex= Olfactory bulbs Architocortex= Hippocampus
- Major neuronal cell types
- -> pyramidal + granular neurons - Cytoachitecture
- -> organized into functional units
Functional units
Refer to columns specialized to process specific inputs + outputs
–> broadmann found areas with different histological organizations, penciled established that these areas correlate with functionally different areas
Subcortical fibre bundels
Relay info to + from specific brain areas
–> depends on their classification as
a) association
b) commissural
c) projection fibers
Association fibres
Interconnect cortical areas within a hemisphere
eg.: short ones connect to adjacent gyri; long ones to more distant ones
Superior longitudinal fasciculus
Association fibre
Spreads out from anterior FL to posterior PL + OL, and connects the overlying cortex of the
a) frontal
b) parietal
c) occipital lobes
–> arcuate fibre is an important subset
Inferior occipitofrontal fasciculus
Association fibre
Located below the insula and runs from the
a) frontal
b) temporal
c) occipital lobes
AND: interconnects them
–> uncinate fasciculus is an important subset
Superior occipitofrontal fasciculus
Association fibre
Located superior + adjacent to corpus callosum
–> interconnects
a) frontal
b) parietal
c) occipital lobes
Cingulum
Located within the limbic lobe
–> interconnects areas of the limbic cortex (=those above limbic system)
=> subset of SOF fibers
Commissural fibres
Connect similar functional areas between the hemispheres
–> enables coordination of cortical activity across the hemispheres
Corpus callosum
Commissural fibre
Largest cortical commissure, that connects the
a) 2 PLs
b) posterior parts of FLs
AND: as their fibers enter the hemispheres they can reach out to all parts of the cortex
Anterior commissure
Connects the
a) anterior temporal lobes
b) olfactory bulbs
Posterior commissure
Located in the midbrain and connects the pretectal nuclei
Projection fibres
Travel to + from the cortex
- via or from the Thalamus
- -> to descend to brainstem, basal ganglia or SC - and come from the corona radiata and converge into the internal capsule
Anterior limb
Located between the caudate + lenticular nucleus
–> part of Internal capsule
Posterior limb
Located between the thalamus lenticular nucleus
–> part of internal capsule
Brodmann’s map
Suggests that the human cortex has 43 cytoarchitectonic areas
- each area in human brain has a number between 1-52
- areas 12-16 + 48-51 are not identifiable in the human cortex but other mammalian species
Which problems arise in the brodmanns map?
Lack of
a) observer independency, reproducibility, objectivity
b) inter-subject variability
- -> maps must be probabilistic
c) inter-individual differences
- -> not all brains are the same
BUT: the relation between cytoarchitecture + connectivity between brain areas was further shown by DTI + fibre tracking, thus the map had a great impact
Large scale functional organisation
Provides insight into how the intrinsic functional architecture of the brain facilitates
- segregation of neural signals
- allows flexible interactions
–> for goal directed behavior
Name the 6 main points that have been discovered about the whole brain network.
- Non random small-world organization
- -> optimal connectivity due to nodes + hubs - Strong inter hemispheric connectivity between homologous regions
- -> heterogenous regions not as their function is lateralized + specialized - Intrinsically organized into multiple coherent networks
- -> segregate specific signals to functional systems + constrain info processing (14 NW) - Brain areas with common patterns of activation/de-activation are organized into distinct brain systems
- Most commonly deactivated brain regions form a default-mode network
- Includes Front-opercular-parietal brain regions
- -> implicated in range of cognitive tasks
Nodes
Represents some predefined collection of brain tissue
–> as the functional NW are co-activated for many tasks, they can flexibly interact to facilitate cross NW signaling
Hubs
Refer to brain areas that are central to communicating info across different brain systems
–> central node
Which brain regions are part of the default mode network?
- PCC
- mPFC
–> functional brain system is important for self-referential info processing
Fronto-opercular-parietal brain regions include the … ?
- Salience network
- -> attentional capture of biologically + cognitively relevant events - Anterior Insula + ACC
- -> signal other brain areas for additional, more goal directed processing - Frontoparietal central executive network
- -> DLPFC + PPC
Axoplasmic transport
Refers to the process that is responsible for the movement of parts of the cell between the soma + synapses
e.g.: proteins, vesicles, Organelles
Anterograde transport
Transport away from soma
(Soma –> synapse)
=> motor protein of conduct is kinesin
Retrograde transport
Transport towards/back to soma
(Synapse –> Soma)
- recycle some of the substances found at the synapse
- inform soma of conditions at the axon terminals
=> motor protein of conduct is dynein
Tracing
Is used to map the connectivity between brain areas
- Delineate the location of the injection site
- Slice the brain
- Create microscopic preparations, that allow to visualize the amount of substances that have arrived in each slice
What are the advantages of the tracing method ?
One learns where specifically the input to a field comes from + where it sends its output to
Disadvantages of the tracing method ?
- Injection site never perfectly matches the field of interest
- Substances may spread into adjacent fields
- Substances affect all neurons in the injection site
- -> not a single one
Pyramidal cells
Are the main output cells of the cortex, with triangular structure
–> project into other regions of brain + spinal cord
(Layers 3+5
Granular neurons/
Stellate neurons
Are the main interneurons, with short axons + dendrites
–> remain within the cortex
Layers 2+4
Agranular vs granular cortex
Refer to cortical areas where there are few (Primary sensory cortex) or a lot granular cells (Primary motor cortex)
Limbic lobe
Is comprised of the cingulate + parahippocampal gyri
–> refers to the area lying just above the limbic system
Splenium
Refers to the posterior pole of the Corpus callosum
–> interconnects the
a) OLs
b) posterior TLs
Genu
Refers to the anterior pole of the corpus callosum
–> interconnects the FLs
Microtubules
Provide the tracks for the proteins/motors that provide fast transport
–> vesicles are then loaded onto motors and carried into or out of soma via microtubules
e.g.: kinesin, dynactin
