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Lecture 2

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University of Toronto St. George

Lecture 2 Synaptic Transmission Electrochemical Potential o When ions diffuse across the membrane they carry a net charge and generate an electrical potential o Net flow = 0 (equilibrium potential) = Nernst equation calculates the potential required to balance the concentration gradient Membrane Potential o Factors contributing to membrane potential: o Distribution of ions across the membrane o Relative permeability of the ions o Charges of the ions o Goldman equation for the calculation of membrane potential (Em) permeability included in this equation; will be somewhere between the potential of all three ions (Na, K and Cl) Conduction with Decrement graded potentials o Change in membrane potential due to the flow of ions o Membrane is degraded with the distance from the synapse Spatial Summation o The two different synaptic potentials can be summed up o Summation added effect of the synaptic input Temporal Summation o Too far apart no temporal summation Action Potentials o Occur only when membrane potential at axon hillock reaches threshold o Three phases: Depolarization Repolarization Hyperpolarization MP more polarized o Absolute refractory period Cell capable of generating a new AP o Relative refractory period More difficult to generate new AP Voltage-Gated Channels responsible for AP o Na channels open first depolarization o K channels open slowly repolarization o Na channels close
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