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Cerebral Cortex Neocortex
6 layers Recent phyolgenetically
Paleocortex 3 layers Older Insular cortex, piriform cortex, primary olfactory cortex
Archicortex
3 layers Older Hippocampal formation
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Microscopic structure
Principalneurons
Aka projection
Pyramidal
Fusiform
Excitatory
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Microscopic structure
InterneuronsStellate
Aka granule
Small
Extensivedendritic tree
Layer IV
Excitatoryinterneuron
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Microscopic structure
InterneuronsHorizontal
Layer I
Development& neonatal
Martinotti
Multipolar
Axon ascends
Deep layers
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Cortical Layers
Layer I MolecularMostly processes
Axons and dendrites
Sparseinterneurons
Horizontal cellsNeuroglia
Synaptic area
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Cortical Layers Layer II External
granular Dense Small and medium-
sized pyramidal &
interneurons Axons and dendrites
Coming here Passing through Pyramidal
Dendrites extend toLayer I
Axons project todeeper layers
Intracortical circuitry
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Cortical Layers
Layer III ExternalPyramidalLarger pyramidals
Dendrites -> Layer I Axons -> deeper
layers, contralateral,
extracorticalprojections
Receives axonsfrom other cortical &extracortical areas
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Cortical Layers Layer IV Internal
Granular Pyramidal cells Stellate/Granule cells Densest layer
Best developed inprimary sensory areas
Input layer V1
Stripe of Gennari Dense band of
horizontally orientedthalamocortical nerve
fibers Hence striate cortex
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Cortical Layers Layer V Internal
Pyramidal Large & medium-sized
pyramidal cells (largest)
Stellate cells
Cells of Martinotti
Least dense
Dendrites project to
superficial layers Axons to mainly:
subcortical, and to othercortical areas
Output layer
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Cortical Layers
Layer VI Multiform
Variety of cells of
different sizes
Primary location of
Martinotti cells
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Cortical Layers Paleocortex &
Archicortex Layers I, V, VI
Neocortex
Layers I-VI
Columnar organization
Modules Inhibit nearby modules
Critical periods
Increase synapticconnections
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Inputs
ThalamusModality specific
Layer IV
Nonspecific
Project diffusely
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Inputs
Extrathalamicmodulatory
Serotonergic
Dopaminergic
Noradrenergic
HistaminergicCholinergic
GABAergic
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Inputs
Association FibersFrom same
hemisphere
Short Nearby regions
Long Distant regions
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Inputs
Association Fibers Long
Superior longitudinalfasciculus
Frontal lobe withother 3
Arcuate fasciculus
Frontal -> speech
areas Cingulum
Core of the cingulategyrus
Frontal ->parahippocampalgyrus
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Inputs
Commissural fibersFrom other
hemisphere
Corresponding andnon-correspondingregions
Travel via corpuscallosum
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Outputs
Association FibersShort
Layer II
Long Layers III & V
CommissuralFibers
Layer III
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Outputs Corticofugal
Output to subcorticalstructures
Corticospinal
Corticoreticular
Corticobulbar
Corticopontine Corticothalamic
Corticohypothalamic
Corticostriate
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Corticospinal Tract
Cortex to motorneurons in the spinalcord
Skilled volitionalmovements
Pyramidal cells in
Layer V Primary motor,
premotor,
somatosensory areas
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Corticoreticular Tract
Cortex to reticular formation in brainstem
Bilateral projections
Predominantly from motor, premotor,
somatosensory areas Accompanies corticospinal tract
Many fibers continue to brainstem nuclei [cranialnerves], thus forming corticoreticulobulbar tract
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Corticobulbar Tract Motor cortex (face
representation) -> motornuclei of cranial nerves Trigeminal, facial,
glossopharyngeal, vagus,accessory, hypoglossal
5 face representations M1, supplementary motor
(M2), rostral cingulategyrus (M3), caudalcingulate gyrus (M4),ventral lateral premotorcortex (LPMCv)
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Corticopontine Tract
Cortex (frontal,parietal, occipital)-> pontine nuclei
Lesions
Contralateral ataxia
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Corticothalamic Tract
Cortical areas thatreceive thalamic input
Feedback
Reciprocal connections
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Corticohypothalamic Tract
Cortex -> hypothalamus Primarily from prefrontal cortex, cingulate
gyrus, amygdala, olfactory cortex,
hippocampus, septal area
i.e. decisions, emotions, memory
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Corticostriate Tract Cortex -> striatum
Direct
Indirect via Corticothalamostriate
Corticopontine -> collaterals Corticoolivary -> collaterals
3 zones:
Sensorimotor Associative
Limbic
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Intracortical Circuitry
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Cytoarchitecture
Architecture of the layersThickness of cortex
Width of the different layers
Cell types in each layerCell density in each layer
Nerve fiber lamination
Define areas based on thisBrodmann areas: 52 of them
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Primary Somatosensory Area (S1)
Postcentral gyrus
Brodmann areas 1-3
Cutaneous: Touch, pain,temperature
Proprioceptive: position, vibration,2-point discrimination
Input from thalamus, commissural,
short association (M1) Outputs: M1, contralateral S1,
association somatosensory cortex(area 5 & 7), thalamus, medulla,
dorsal horn of spinal cord
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Primary Somatosensory Area (S1)
Area 1Cutaneous or
proprioceptive
Area 2 & 3AProprioceptive
Area 3BCutaneous
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Somatosensory Homunculus Body
Representation
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Somatosensory Association Areas Perception of shape, size, texture
Stereognosis Identification of objects by contact
Area 5
Goal-directed voluntary movements Manipulation of objects
Tool use/body image
Area 7 Integration of visual and somatosensory stimuli
Hand-eye coordination
Fake arm study
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Primary Visual Cortex (V1)
Surface of theoccipital lobe &calcarine sulcus
Area 17
Striate cortex
Band of Gennari
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Inputs to V1 Retina to LGN
Via opticnerve, optic
chiasm, optictract
LGN to V1
Via opticradiations
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V1: Visual Field Representation Contralateral Visual
Field
Contralateral Eye:
Nasal retinaprojections cross atoptic chiasm
Ipsilateral Eye: Temporal retina
projections pass
straight through
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V1: Central vs Peripheral
Central:
Macula
Fovea
Cones and RodsOccipital surface
PeripheralMostly Rods
Calcarine sulcus
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V1
Cortical magnification
Phosphenes
Cortical blindness
Blindsight
Lesions:
Can be macular-sparing
Vascular damage to calcarine sulcus
Occipital surface spared
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Extrastriate Cortex Later stages of
visual processing 2 pathways
Ventral:
What Dorsal
Where
Lesions causevarious disorders Prosopagnosia Akinetopsia
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Primary Auditory Cortex (A1)
Superior temporalgyrus
Areas 41 & 42
Input from medialgeniculate nucleus
StimulationTinnitus
Buzzing, humming,knocking
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Auditory Association Cortex Area 22
Wernickes area (dominant hemisphere) Comprehension of speech Lesion
Receptive aphasia Cannot comprehend spoken words
Nondominant hemisphere Non-speech
Environmental sounds Musical melodies Tonal qualities
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Primary Gustatory Cortex Area 43
Parietal operculum
Taste
Input from posteroventral medial nucleusof the thalamus
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Primary Olfactory Cortex Piriform cortex
Tip of temporal lobe
Input bypasses thalamus
Discriminates different odors
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Primary Vestibular Cortex Lateral cortical temporoparietal area
Lesions
Impair preception of body orientation and
movement
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Cortical Motor Areas Primary Motor (M1)
Supplementary Motor Area (SMA/M2)
Premotor area (PMv and PMd)