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4. Na+ channels and Action Potential Initiation. Action potentials are often initiated at the axon hillock, where the axon leaves the cell body. The axon hillock has a high density of Na+ channels, which lowers the threshold for initiating an action potential. MetaNeuron can be used to measure the effect of Na+ channel density on the threshold of action potential generation. Vary "gNa max" from 200 to 380 mS/cm2 in 20 mS/cm2 steps. (Na+ channel density is proportional to gNa max.) For each "gNa max" value, determine the threshold stimulus amplitude (in μA) for initiating an action potential. Plot the threshold current as a function of gNa max. Why does the action potential threshold vary as Na+ channel density is changed? 5. Action Potential Membrane Conductances. Starting with the default parameter values. Select "Show ionic conductances" in the "Conductances and Currents" window. The green and blue Iraces show the time course of the Na+ and K+ conductances that are activated during the action potential. Why does the K+conductance turn on slower and last longer than the Na+ conductance? 6. Action Potential Membrane Currents. Select "Show ionic currents" in the "Conductances and Currents" window. The green and blue traces show the time course of the inward (negative) Na+ current and the outward (positive) K+ current that generate the action potential. Why does the initial phase of the Na+ current have an inflection point?

4. Na+ channels and Action Potential Initiation. Action potentials are often initiated at the axon hillock, where the axon leaves the cell body. The axon hillock has a high density of Na+ channels, which lowers the threshold for initiating an action potential. MetaNeuron can be used to measure the effect of Na+ channel density on the threshold of action potential generation. Vary "gNa max" from 200 to 380 mS/cm2 in 20 mS/cm2 steps. (Na+ channel density is proportional to gNa max.) For each "gNa max" value, determine the threshold stimulus amplitude (in μA) for initiating an action potential. Plot the threshold current as a function of gNa max. Why does the action potential threshold vary as Na+ channel density is changed? 5. Action Potential Membrane Conductances. Starting with the default parameter values. Select "Show ionic conductances" in the "Conductances and Currents" window. The green and blue Iraces show the time course of the Na+ and K+ conductances that are activated during the action potential. Why does the K+conductance turn on slower and last longer than the Na+ conductance? 6. Action Potential Membrane Currents. Select "Show ionic currents" in the "Conductances and Currents" window. The green and blue traces show the time course of the inward (negative) Na+ current and the outward (positive) K+ current that generate the action potential. Why does the initial phase of the Na+ current have an inflection point?

Human Anatomy & Physiology (11th Edition)
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
Section: Chapter Questions
Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...
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4. Na+ channels and Action Potential Initiation. Action potentials are often initiated at the axon hillock, where the axon leaves the cell body. The axon hillock has a high density of Na+ channels, which lowers the threshold for initiating an action potential. MetaNeuron can be used to measure the effect of Na+ channel density on the threshold of action potential generation. Vary "gNa max" from 200 to 380 mS/cm2 in 20 mS/cm2 steps. (Na+ channel density is proportional to gNa max.) For each "gNa max" value, determine the threshold stimulus amplitude (in μA) for initiating an action potential. Plot the threshold current as a function of gNa max. Why does the action potential threshold vary as Na+ channel density is changed? 5. Action Potential Membrane Conductances. Starting with the default parameter values. Select "Show ionic conductances" in the "Conductances and Currents" window. The green and blue Iraces show the time course of the Na+ and K+ conductances that are activated during the action potential. Why does the K+conductance turn on slower and last longer than the Na+ conductance? 6. Action Potential Membrane Currents. Select "Show ionic currents" in the "Conductances and Currents" window. The green and blue traces show the time course of the inward (negative) Na+ current and the outward (positive) K+ current that generate the action potential. Why does the initial phase of the Na+ current have an inflection point?
Transcribed Image Text:4. Na+ channels and Action Potential Initiation. Action potentials are often initiated at the axon hillock, where the axon leaves the cell body. The axon hillock has a high density of Na+ channels, which lowers the threshold for initiating an action potential. MetaNeuron can be used to measure the effect of Na+ channel density on the threshold of action potential generation. Vary "gNa max" from 200 to 380 mS/cm2 in 20 mS/cm2 steps. (Na+ channel density is proportional to gNa max.) For each "gNa max" value, determine the threshold stimulus amplitude (in μA) for initiating an action potential. Plot the threshold current as a function of gNa max. Why does the action potential threshold vary as Na+ channel density is changed? 5. Action Potential Membrane Conductances. Starting with the default parameter values. Select "Show ionic conductances" in the "Conductances and Currents" window. The green and blue Iraces show the time course of the Na+ and K+ conductances that are activated during the action potential. Why does the K+conductance turn on slower and last longer than the Na+ conductance? 6. Action Potential Membrane Currents. Select "Show ionic currents" in the "Conductances and Currents" window. The green and blue traces show the time course of the inward (negative) Na+ current and the outward (positive) K+ current that generate the action potential. Why does the initial phase of the Na+ current have an inflection point?
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