Lecture 3-action potential II

Lecture 3-action potential II - Todays Lecture 1) Review...

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1 Today’s Lecture 1) Review the principles that create the resting potential. 2) Introduce Ohm’s Law. 3) Show how an oscilloscope works and how it is used to measure membrane potentials. 4) Introduce voltage gated ion channels and they operate. 5) Discuss how voltage gated Na + and voltage gated K + channels generate action potentials. 6) Consider how the operation of those channels allows for the propagation of an action potential along the entire length of an axon.
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2 Electrical pulse (Action Potential) starts here Release of neurotransmitter + + + + Neurotransmitter binds to receptor and opens an ion channel. Positive current is injected into neuron carried by Na+ + -
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3 In thinking about action potentials, keep your eye on the ball ! The whole idea of the action potential is to transmit information: 1) Over long distances 2) With high fidelity, so that the same action potential that appears near the cell body, appears at the terminal a short time later. 3) Rapidly
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4 Inside of Cell With efflux of + charges, inside of cell becomes slightly negative Additional efflux (loss) of K+ generates progressively larger negativity inside of cell Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Concentration force Electrical force
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5 Inside of Cell Concentration gradient continues to drive K+ out of cell. Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - However, the building negativity inside begins to attract some K+ back into cell. Concentration force Electrical force
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6 Inside of Cell Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Inside negativity continues to build until for each K+ driven out of the cell by concentration forces, an equal number are attracted back by electrical forces This potential defines the potassium equilibrium potential (E K ) Concentration force Electrical force
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7 Inside of Cell Inside is so negative so that for each K+ driven out of the cell by concentration forces, and equal number are attracted back by electrical forces Cell is at (E K ) -potassium equilibrium potential Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Concentration force Electrical force
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8 Inside of Cell Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + The membrane has some Na channels but is much more permeable to K+ than to Na+
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9 58 = log [K] o [K] i = 58 log 400 mM 20 mM = -75.4 mV Concentration (mM) Intracellular Extracellular Relative permeability Ion K+ 400 20 1.0 Na+ 50 450 0.01 Cl- 40 560 0.10 = 58 log V membrane potential P Cl P K P Na P K [K] o [K] i [Na] i P Na [Na] o [Cl] o P Cl [Cl] i + + + + = -70.18 mV E K 58 = log [Na] o [Na] i = 58 log 50 mM 450 mM E Na = +55 mV
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10 Inside of Cell Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na +
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11 1 2 3 4 The Na/K ATPase pump accounts for 20-40% of the brain’s energy consumption
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12 Na + Inside of Cell Na + Na + Na + Cl - Cl - Cl - Cl - Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - K+ Cl- Na+ Na-K pump
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13 I will frequently use the term: Driving Force Driving force refers to the net force acting on an ion Driving force is the difference between the membrane potential and the equilibrium potential for that ion.
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This note was uploaded on 10/25/2010 for the course BIO 365R taught by Professor Draper during the Spring '08 term at University of Texas at Austin.

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Lecture 3-action potential II - Todays Lecture 1) Review...

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