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RMP and AP propagation

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Western University
Physiology 3120
Tom Stavraky

Human Physiology Monday, September 28, 2009 Resting Membrane Potential • Resting membrane potential  Membrane permeable to a variety of ions, so can’t use the Nernst equation  Each ion affects the RMP depending on its permeability & concentration gradient  Therefore use the Goldman equation • Goldman equation  No valence in the equation because the charge is taken into account based on the position of the ion in the equation  Shows  Important ions (K, Na, and Cl) and their concentration gradients  Degree of importance of each ion at a particular time is proportional to membrane permeability • RMP = -70mV (can vary from cell to cell)  This potential maintains the concentration gradient of chloride  Some potassium will leak out because the RMP isn’t strong enough to counter the movement of potassium  Potassium moved back in using the Na/K pump  Sodium (whose equilibrium potential is much higher than the RMP) theoretically should move down its gradient, but membrane is less permeable to sodium than potassium  Cells in the heart don’t have an RMP Ionic Basis & Propagation of the Action Potential • Neuron  Excitable cells (i.e. capable to self-generating electrochemical impulses)  Parts  Soma/cell body (contain all the organelles)  Dendrites (receive signals from other neurons)  Axon (send signals to other neurons/muscles via the nerve terminals) • The action potential  Initiated at the axon hillock by a depolarizing stimulus  Not completely dependent on each other because one can function without the othe
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