Task 4 - organization of cerebral cortex Flashcards
Neocortex vs Paleocortex, Archicortex
-Neocortex: most of human cortex, 6 layers
- Paleocortex: in olfactory bulb
- Archicortex: hippocampus
- > older areas of cortex, 3 layers
Major neural cell types in the cortex
- pyramidal
- granular
Pyramidal cells
- layer 3 and 5
- axons project out of cortex into other regions of the brain and spinal cord
- main output cells of cortex
- primary motor cortex: large number of pyramidal neurons -> to lower motor areas -> via corticospinal and corticobulbar tracts
- primary motor cortex also referred to as ‘agranular cortex’
Granular cells
- layers 2 and 4
- ‘stellate neurons’
- shorter axons, smaller dendrites
- remain within cortex, main interneurons
- primary sensory cortex has a lot (‘granular cortex’)
Layer 1 and Layer 6
- layer 1: molecular layer, mainly neuronal processes
- layer 6: multiform layer, output neurons of varying shapes and sizes
Cytoarchitecture
- functional units -> cortical columns
- > specialized to process specific inputs/outputs
- > cytoarchitecture of columns depends on function
different subcortical fibers (3)
1) Association
2) Commissural
3) Projection
Association fibers in general
- interconnect areas within one hemisphere
- short ones -> adjacent gyri, sulci
- long -> more distant areas
Association fibers (a,b,c,d)
a) superior longitudinal fasciculus, arcuate fasciculus
b) inferior occipitofrontal fasciculus, uncinate fasciculus
c) superior occipitofrontal fasciculus
d) Cingulum
superior longitudinal fasciculus
- most compact in midportion, above insula
- spreads to frontal lobe anteriorly and to parietal and occipital lobes posteriorly
inferior occipitofrontal fasciculus
- below insula
- frontal -> through temporal -> to occipital
cingulum
- deep in cingulate and parahippocampal gyri (limbic lobe)
- connects areas of the limbic cortex
Superior occipitofrontal fasiculus
-
Superior occipitofrontal fasiculus
- adjacent and superior to corpus callosum
- connects frontal, parietal and occipital lobes
commissural fibers in general
- connect areas of cortex in one hemisphere with some areas in opposite hemisphere
- majority of commissural fibers cross the midline in largest cortical commissure (corpus callosum)
commissural fibers (a,b)
a) corpus callosum
b)
corpus callosum
-connects to parietal lobes and posterior parts of frontal lobes
corpus callosum
- connects to parietal lobes and posterior parts of frontal lobes
- fibers enter hemispheres and fan out to reach all parts of cortex
- forceps minor: anterior end
- forceps major: posterior end
Genu
- anterior of cc
- connect 2 frontal lobes
splenium
- posterior pole of cc
- connects occipital lobes and posterior temporal lobes
anterior commissure
connects anterior temporal lobes and olfactory bulbs
posterior commissure
-located in the midbrain and connects pretecal nuclei
Projection fibres in general
- travel to and from the cortex
- to/from thalamus
- descend to basal ganglia, brainstem, spinal cord
-internal capsule
Anatomy of internal capsule
- V shaped in horizontal section
- anterior limb: between caudate and lenticular nucleus (GP and putamen)
-posterior limb: between thalamus and lenticular nucleus and genu, where two limbs meet
2 approaches to solve problem of high complexity and structural variability between individuals
1) volumetric approach: define outer boundaries of cerebrum and anterior and posterior commissure -> then rescale subvolumes according to a specific brain -> problem: when 2 different brains are put in same system they don’t align
2) cortex surface based approach: alignment of cortices of individuals brains (aufpumpen)
Axpolasmatic transport
- process responsible for movement of organelles (mitochondria), lipids, proteins, synaptic vesicles and other parts of cell membrane to and from the soma
- > down the axon to the synapse and back up to soma
microtubules
- run along length of axon and provide main cytoskeletal tracks for transportation
- motor proteins (Kinesin, Dynein) bind and transport different cargoes
Axonal transport can be fast/ slow and in different directions:
- Anterograde: from soma to axon tip/cell body to synapse, cell membrane
- > mediated by Kinesins
- Retrograde: from synapse/plasma membrane -> to cell body / soma
- mediated by Dynein
- > source of recycling substances found at synaptic ending+ informs soma of conditions at axon terminals
global brain architecture: small world architecture
- network in which constituent nodes exhibit a large degree of clustering
- a dense local clustering of connections between neighbouring nodes
- short span length between nodes due to relatively few long-range connections
- > minimizes wiring
- > high specialization and high integration
global brain architecture: hub , edges
- hub: node that is central to communication across different brain systems ( discussion leader)
- module: cluster of nodes
- > modular organization in brain
- edge: connection between two nodes
- > edges are not random, they are the most ideal connection there is
global brain architecture - hemispheric connectivities
- highest correlation is among the primary sensory cortices
- left hemisphere: strong bias towards intrahemispheric connectivity: language and motor coordination
- right hemisphere: visuospatial and attentional processing -> stronger connectivities with homologous regions in the left hemisphere
- > interhemispheric bias
global brain architecture - networks
-many brain areas that are engaged during diverse sets of cognitive tasks also form a coherent large-scale network that can be readily identified
global brain architecture - activated and deactivated brain systems
- neural plasticity
- > in some systems supressed
- > other systems are preferentially actively engaged in processing task-relevant info
- > responses within these regions increase/decrease proportionately and often antagonistically in relation to specific cognitive demands
default-mode network
- important for:
- self-referential mental processes
- self-monitoring
- other cognitive functions that support self-referential mental activity
- brain regions that are deactivate during wide range of cognitive tasks
- > posterior cingulate gyrus and medial PFC
- active during:
- > episodic memory retrieval
- > autobiographical memory
- > internal speech
-> activity mediated by salience network
salience network
integrates brain signals involved in conflict monitoring, interoceptive-autonomic and reward-processing areas into a common salience network
-attentional capture and signaling to other brain systems
- anterior insula and anterior cingulate cortex
- strong links with paralimbic and limbic areas
central executive network
- actively maintaining and manipulating information in the working memory, for rule-based problem-solving and decision-making in the context of goal-directed behaviour
- Dorsolateral and ventrolateral prefrontal cortices and the supramarginal gyrus
- > dynamic interactions between these networks regulates shifts in attention and access to goal-relevant cognitive resources
example default mode/salience/executive network
- you are in a lecture, just dreaming instead of listeniing
- > default mode network is active
- Suddenly, you hear a word that sounds important
- > salience network kicks in
consider the stuff that caught your attention to be important
-> salience network mediates a shift from the default mode network to central executive network
