chapters 17 18 single

8/14/2019 Chapters 17 18 Single

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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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InterneuronsStellate

Aka granule

Small

Extensivedendritic tree

Layer IV

Excitatoryinterneuron


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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)

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