Synaptic plasticity

Definition Alteration of synapse response to input

Synaptic plasticity Relevance –Adapting to environment –Neurodevelopment –Learning & memory

Examples PTP versus fatigue LTP vs LTD

LTP NMDA hypothesis

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

Spike timing Variant of Hebbian learning –Donald Hebb (1949) NMDA Dependent Reversible strengthening is function of EPSP-spike delay

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

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

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)

Membrane properties R M (per unit length) =  d R I (per unit length) = 4  /  d 2 C M (per unit length) = c  d