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Published byMoses Marshall Davidson Modified over 9 years ago
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Synaptic plasticity
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Definition Alteration of synapse response to input
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Synaptic plasticity Relevance –Adapting to environment –Neurodevelopment –Learning & memory
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Examples PTP versus fatigue LTP vs LTD
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LTP NMDA hypothesis
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LTP Presynaptic modification –AA → G-protein –NO → GC Postsynaptic modification –CaM Kinase II –cAMP, cGMP-dependent –Tyrosine kinase (fyn) Synaptic structure –widening of neck of spine Glutamate release TF Activation Receptor Upregulation
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Spike timing Variant of Hebbian learning –Donald Hebb (1949) NMDA Dependent Reversible strengthening is function of EPSP-spike delay
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Integration Convergence of much information –Input:up to 10,000 synapses + sensory input –Output:one axon Time dependent –Long term state of cell –State of receptors + membrane in short term Each synapse different –distance from soma, other synapses –neurotransmitter combination –receptor types, number and sensitivity
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Neuronal mechanisms of integration Dendritic tree –diameter –voltage gated ion channels EPSP and IPSP –temporal + spatial summation –decay with distance and time –shunting inhibition Axon hillock –threshold behaviour
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Calcium mediated integratory effects Repetitive firing Adaptation Accommodation Delay firing Subthreshold oscillation LTP / LTD (De-)sensitisation Down- / Upregulation Synaptic growth Fast (ionic)Slow (second messenger)
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Membrane properties R M (per unit length) = d R I (per unit length) = 4 / d 2 C M (per unit length) = c d
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