(1) Cerebral Cortex

(1) Cerebral Cortex - Weapons in neurophysiologist s armory...

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1 Weapons in neurophysiologist ` s armory • Recording – Individual neurons – Gross potentials – Brain scans • Stimulation • Lesions – Natural lesions – Experimental lesions Cerebral Cortex • Every cubic inch of cerebral cortex has about 10,000 miles of nerve fibers in it • The number of neurons in the brain is about 30 X greater than the number of humans on the planet. (180 billion) • A typical neuron is wired to about 1000-2000 of its neighbors – It is the pattern of these connections that determines what the brain does Cerebral Cortex • Humans are quite good at storing & processing sensory information – So we can use it better in making effective responses to our environment • Immense degree of convergence and divergence from one neuron to another – Most cortical neurons are a site of converging input from multiple neurons and source of diverging output to multiple neurons Cerebral Cortex Silent Areas • Most areas of the cortex neither respond in an obvious way to: – simple sensory + – nor produce movements when electrically + The Cerebral Cortex • Layer I -Molecular Layer – mostly axons • Layer II-External Granule Layer – granule (stellate) cells • Layer III-External Pyramidal layer – primary pyramidal cells Cerebral Cortex • Layer IV-Internal Granule Layer – main granular cell layer • Layer V- internal pyramidal layer – dominated by giant pyramidal cells • Layer VI- multiform layer – all types of cells-pyramidal, stellate, fusiform
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2 Cerebral Cortex • Three major cell types – Pyramidal cells • souce of corticospinal projections • major efferent cell – Granule cells • short axons- – function as interneurons (intra cortical processing) – excitatory neurons release 1 o glutamate – inhibitory neurons release 1 o GABA – Fusiform cells • least numerous of the three • gives rise to output fibers from cortex Cerebral Cortex • Most output leave cortex via V &VI – spinal cord tracts originate from layer V – thalamic connections from layer VI • Most incoming sensory signals terminate in layer IV • Most intracortical association functions - layers I, II, III – large # of neurons in II, III- short horozontal connections with adjacent cortical areas Cerebral Cortex • All areas of the cerebral cortex have extensive afferent and efferent connections with deeper structures of brain. (eg. Basal ganglia, thalamus etc.) • Thalamic connections (afferent and efferent) are extremely important and extensive • Cortical neurons (esp. in association areas) can change their function as functional demand changes Secret of the Cerebral Cortex • Resultant network of links between neurons in the cortex mimics relationships between things in the outside world – Probabilistic model of the world in the brain which can predict what is likely to happen next • Mechanism for making the strength of these connections change to reflect observed associations is the secret of the CC
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(1) Cerebral Cortex - Weapons in neurophysiologist s armory...

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