Cortex Flashcards
Cortex means?
bark
Pallium means?
shell
-embryonic structure of cortex
Gross Structure of Cortex?
- dominated by convoluted gyri and sulci
- laminar structure with many diff. cell types
Cerebral Cortex Prenatal Development
-outpocketing of Prosencephalon (most anterior part of neural tube)
-its a telencephalic structure (2 cerebral hem. form laterally on either side of the telencephalon)
~100 days, grows over most of brain
Lissencephalic
-smoothness of cortex until 6 months gestation
Gyrencephalic
-cortex surface with ridges & valleys to package it
Brain to Body Weight Ratio
helps normalize brain size differences b/w species
Weight of human brain
3-4 lbs.
Is there a correlation b/w brain size & intelligence within humans?
no
Lobes of the Cerebral Cortex?
- Frontal Lobe (frontal pole to central sulcus)
- Parietal Lobe (central sulcus to imaginary line connecting the preoccipital notch to the parietooccipital sulcus)
- Occipital lobe (line to occipital pole)
- Temporal Lobe
3 Types of Cortex (histology)?
- allocortex
- isocortex
- mesocortex
Allocortex
-3 layered
Isocortex
-6 layered, I to VI starting from pia surface, layer I is cell poor
Mesocortex
-less regular, 3-5 layers
3 Types of Cortex (origin)?
- Paleocortex (oldest, olfactory) - formed from lateral pallium
- Archiocortex (next, hippocampal formation) - formed from medial pallium
- Neocortex (new, isocortex) - formed from dorsal pallium
Isocortex Layers
I - molecular layer, poor in cells (GABAergic interneurons)
II & III - continuous & hard to tell apart from one another, superficial pyramidal cell layer
IV - contains many small cells (granular layer)
V - deep pyramidal cell layer (largest pyramidal cells)
VI - multiple cell types (polymorphic layer)
V & VI - subgranular layers, I-III supragranular
Pyramidal Cells
- pear-shaped soma & a single dominant apical dendrite
- send axons to deep white matter & are projection neurons of cortex, local collaterals
- variable density of spines
- project locally & to other cortical/subcortical areas
- excitatory (glutamate or aspartate)
- Apical Dendrite, Basal Rosette of Dendrites, Axon
Nonpyramidal Cells
- GABAergic interneurons (local circuit neurons that only project locally within a given area of cortex)
- multipolar or bipolar
- in layer IV of primary sensory cortex, glutamate is used as neurotransmitter (spiny stellate cell) - local
GABAergic interneurons?
-aspiny or very sparsely spiny
Nonpyramidal cell types?
- chandelier
- basket
- neuroglia form
- bipolar
Basket Cells
- nonpyramidal cell
- layers II/III and V
- vary in size
- multipolar and axons have basket-shaped terminations that surround somas of pyramidal cells
Chandelier Cells
-axonal terminations, cassettes of which contact the initial segments of pyramidal neurons & collectively make the cell look like a chandelier
Bipolar & Bi-tufted cells
- cells have long dendrites & axons that are organized vertically as opposed to the more horizontal organization of basket & chandelier cells
- tend to innervate more distal dendrites of pyramidal neurons (compared to chandelier or basket cells)
Dominant Input to most cortical neurons?
- comes from other cortical neurons
- excitatory pyramidal neurons are highly interconnected
Main extrinsic input to the cortex comes from?
-the thalamus
others are: widely-projecting brainstem nuclei which serve modulatory functions (locus ceruleus, raphe nuclei, ventral tegmental area, & basal forebrain nuclei
2 Types of Thalamic Input to Cortex?
- Specific - from thalamic nuclei that project to a single cortical areas & typically concerns a single modality (VL to motor cortex, VPL for somatosensory cortex, lateral geniculate for visual cortex, or medial geniculate to auditory cortex
- layer IV - Non-specific - comes from thalamic nuclei that integrate info from many sources & this input is thought important for general brain states & arousal (intralaminar & midline thalamic nuclei)
- layer I
Path of all extrinsic inputs to enter the cortex?
-enter from deep white matter & travel vertically
Cortical Outputs?
- Cortico-cortico connections - layers II & II (pyramidal)
- include association fibers that project ipsilaterally (local & long distance) & callosal projections (cortralateral cortex via the corpus callosum)
Layer V Pyramidal Neurons
- pyramidal neurons are the main output of cortex in general
- project to various subcortical regions, including the spinal cord (corticospinal tract), pons (corticopontine), tectum (corticotectal), & basal ganglia (corticostraiatal)
Layer VI Pyramidal Cells
- primarily project to thalamus
- thalamus projects to cortex & cortex projects back to the same areas of thalamus (feed-back loop)
- basis for several thalamocortical rhythms in EEG (sleep-wake cycle, consciousness)
Cortical White Matter
-axons of cortical projection neurons have different targets
Layers II & III - primarily project to the contralateral cortex (commissural) or other cortical areas on the same side of the brain (associational)
-may project to striatum
Layer V - (superficial) cells are thinner with less robust apical dendrite, project to contralateral cortex & to subcortical telencephalic targets like the striatum (deep) robust in form & tend to project beyond the telencephalon
Basis of Neural Diseases
-subtle changes in balance of excitation to inhibition in local cortical circuits `
Mini Column
-all cells encode similar features
Microcolumn or Hyper column
-encompass all of the cells allied together for a particular function
What are cortical columns?
10000 macrocolumns act as a basic functional unit and are made up of 200 cells minicolumns (vertical arrangement of cells in local circuits that encode similar features). Layer 4 spiny stellates get thalamus input, then excite 5 and 6 pyramidal cells (5 gives output locally, to other cortex, and subcortically); interneurons exist laterally in columns for regulation.
How does the cortex work?
-functions can be localized within the cortex
How can cortical areas be classified?
- Histology (Brodmann’s, for example prefrontal cortex is homotypic because all 6 layers are obvious but primary sensory is heterotypic granular (large 4, small 5) while primary motor is heterotypic agranular (small 4, large 5)), connections (each part gets input from thalamus, i.e. VPL/VPM for somatosensory, VL for motor), or function.
(sensory modalities first go to their respective cortex, then are processed first at unimodal association areas and then combined with other senses at heteromodal ones; motor functions also have association processing, hence why most of the cortex is association and not simple motor or sensory).