Lecture 04 Action Potential

# Lecture 04 Action Potential - The Action Potential Chapter...

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The Action Potential Chapter 4

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Action Potentials • Action potentials are the signals the nervous system uses to send information • During rest the inside of a neuron is negatively charged relative to the outside. This is the resting membrane potential and it is about -65 mV • During an action potential the inside of the neuron briefly becomes positively charged compared to the outside
From 0 mV to -80 mV by opening K+ channels All channels closed. Membrane potential 0 mV K+ channels open. K+ ions flow out of cell. Inside becomes negatively charged compared to outside Equilibrium potential for K reached. Membrane potential is -80 mV. No net K+ current, equal number of ions leave and enter

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(a) Starting at equilibrium potential for K+ (E K ), -80mV (b) Na+ channels open. Na+ ions (positively charged) rush in and make inside positive. Membrane potential depolarize. K+ ions also start to flow out because voltage has moved away from E K , but Na+ rushes in so fast that membrane potential briefly approach E Na (c) Na+ channels close. K+ ions rush out because of large driving force, taking their positive charges with them to make the inside negative (d) Resting membrane potential restored. Inside is again more negative than outside
I ion = g ion (V m –E ion ) g = conductance = permeability I ion = ionic current V m = membrane potential E ion = equilibrium potential for the ion Based on Ohm’s Law: V = R I Æ I = V / R • Membrane conductance used instead of resistance. Conductance (g )= 1 / R. Conductance corresponds to the number of open ion channels • Electrical driving force is the difference between V m and E ion Mathematical description of membrane current Current (I) is zero if g is zero (if channels are not open, or when V m –E ion = 0, that is at the equilibrium potential for the ion)

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IV-curve assumes channels are open E K = -80mV E Na = +62mV inward current outward current I V Can be used to determine when currents reverse (goes from inward to outward), and the relative size of the current through a single channel at different voltages
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## This note was uploaded on 04/03/2008 for the course CELL BIO & 245 taught by Professor Schjott during the Spring '08 term at Rutgers.

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Lecture 04 Action Potential - The Action Potential Chapter...

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