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Cellular structure of cortex


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Molecular Layer
Superficial layer, rich in axon and dendrite fibers horizontally oriented.
Relatively few cell bodies (neurons)
No inputs or outputs
External Granular layer
Layer 2; mostly small neurons, a few small pyramidal neurons. input from layer 3 association fibers.
External pyramidal layer
Layer 3; medium-sized pyramidal cells, which give association and commisural fibers
pyramidal cells
have apical dendrites and several basal dendrites, give the cell a pyramidal shape.
internal granular layer
layer 4; composed of stellate neurons, and a few pyramidal neurons. Mostly receives thalamus input, especially in the primary somatosensory cortex.
internal pyramidal layer
layer 5; medium/large pyramidal cells, giant Betz pyramidal cells. these are so big cuz they project to subcortical areas.
multiform layer
layer 6; mixed bag; includes stellate, pyramidal neurons. the pyramidals project to thalamus.
cell types in the neocortex
glial, neurons
neuron cell types in neocortex
stellate, pyramidal, basket
glial cell types
microglia, oligodendrocytes, astrocytes
Divisions of the cortex
Isocortex (neo);
allocortex: paleocortex and archicortex
olfactory center is an example
hippocampal formation is an example
half of brain's volume
comprised of the cerebral cortex
cortical connection fiber types
association, commisural, projection
association fibers
interconnect cortex within the same hemisphere; primarily in layer 3 to layer 2
arcuate fibers
short association fibers that connect adjacent gyri
longitudinal association fibers
long, intercortical connections; like cingulate gyrus, superior/inferior occipitofrontal fasciculi, uncinate fasciculus.
commissural fibersq
interconnect the two cerebral hemispheres; such as corpus callosum, or anterior/posterior commisure.
corticofugal systems
projection fibers from the cerebral cortex layer 5 (large/giant betz pyramidal cells) to subcortical structures. 7 different systems
corticothalamic system
projection fibers from layer 5 of cortex to thalamus
corticosubcortical system
a re-entrant circuit; corticostriatal is an example, as it goes from corticostriatopallidothalamocortical loop. basically starts in cortex and ends in cortex.
projection fiber from layer 5 of cortex 1) red nucleus, then subcortical structure
2)red nucleus to IO to cerebellum
corticopontine system
a projection system from layer five of cerebrum to the pons then to the cerebellum
projection fiber system from layer 5 of the cerebrum to the reticular structures to subcortical structures
corticobulbar system
corticofugal system from the cortex layer 5 through the internal capsule, descend into the brain stem, emerge on either side of the mesencephalon as the cerebral peduncles, then synapse on lower motor neurons of c.n. 5,7, 9-12.
Motor inputs via superior colliculusand reticular formation for eye movement coordination.
corticofugal projection system from the 5th layer of the cortex through the internal capsule in three tracts: corticobulbar, lateral corticospinal and anterior corticospinal; the tracts exit the internal capsule on either side of mesencephalon as cerebral peduncles.
7 corticofugal systems
corticothalamic, corticosubcortical, corticopontine, corticorubral, corticoreticular, corticospinal, corticobulbar. all project from layer 5 except corticothalamic, from layer 6

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