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Ch 3 Computing Brains

Ch 3 Computing Brains - Ch 3 Computing Brains 1 Brain has...

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Ch 3 Computing Brains 1. Brain has several diff levels of organization: lobes, nuclei, nerve tracts, cytoarchitectonic areas (spatial distribution of cell shapes and sizes) and interconnections, neurons, subcellular structures (synapses), molecular structures *** what’s important is the collective state of its neurons 2. The building blocks: neurons and synapses a. Neurons i. Horace Barlow: functioning of the brain best understood at level of neurons ii. Basic representational unit of the brain iii. Wired together in an orderly manner iv. Sends signals to other neurons by emitting all-or-none impulses (action potentials/spikes) whose timing and frequency reflect various qualities of its combined inputs v. Hyperpolarized depolarized repolarized vi. Action potentials traverse the axon before splitting (arborizing) to other neurons at synapses b. Synapses i. Narrow gap between axon of a presynaptic neuron and cellular membrane of the postsynaptic neuron ii. Electrochemical: spike causes release and diffusion of neurotransmitters into synaptic gap iii. Efficacy low; near-simultaneous action of many presynaptic neurons needed for postsynaptic neuron to fire iv. Modifies transmitted signal: output a function of a weighted sum of its inputs, each weight controlling contribution of an input v.
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