Ch2part2

Ch2part2 - Ch 2 CELLS OF THE NERVOUS SYSTEM Continued What...

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CELLS OF THE NERVOUS SYSTEM Continued Ch 2
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What Causes the Membrane Potential? +ve charge outside and –ve charge inside Large molecules carry a negative charge and never leave the neuron More Na+ ion outside more K+ ion inside as a protein called the sodium-potassium transporter lets 3 (Na+) ions out per 2 (K+) ions in. Protein channels let some ions pass but not other ions to create environments with charges.
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Why Does the Membrane Potential Change? Two Primary Forces on Ions 1. Diffusion : • The process whereby molecules distribute themselves evenly throughout water • Move from high to low concentrations 2. Electrostatic Pressure : The pressure exerted by charges: • like charges repel (+ +) or (- -) • opposite charges attract (+ -)
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+ve outside –ve inside More Na + ion outside more K + ion inside Na + -K + ATPase pumps out 3 Na + ions and pumps in 2 K + ions Voltage gated K + channels open so K + goes out. Voltage gated Na + channels closed. More –ve charged proteins inside Fig 2.10 from Meyer and Quenzer Distribution of Ions Across the Neuronal Membrane at Rest
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Intracellular Fluid: The fluid contained within cells Extracellular Fluid: The fluid contained outside cells Charge of the INSIDE of a Neuronal Membrane at rest: -70 mV Fig. 2.18 Forces on Ions Across a Neuronal Membrane at rest
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Action Potential (AP): A rapid reversal of the membrane potential An action potential is triggered when the threshold of excitation (or threshold of activation) is reached, which is approximately -55 mV.
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Characteristics of an Action Potential 1. All or None Law 2. Found in axons only (not soma) 3. Voltage-dependent 5. Involves sequence of Na+ then K+ channels opening 6. Action Potential has a typical bell shape
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This note was uploaded on 03/24/2009 for the course PGS 24674 taught by Professor Biswas during the Spring '09 term at ASU.

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Ch2part2 - Ch 2 CELLS OF THE NERVOUS SYSTEM Continued What...

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