Homework_03_solution - describe or draw their effects on...

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BME 402 Homework 3 Due 11am, 2/7/06 Hodgkin-Huxley What makes an action potential? You should be able to draw what is happening to g Na and g K during an AP in either current clamp or voltage clamp mode. Given the plots of n , τ n , etc., you should be able to plot exactly, by inspection (i.e. without calculation), the time course of n, m, or h in response to a series of constant voltage steps. Understand the notion of a gating particle, and why HH tried multiplying variables together to predict channel open probabilities. You should know how to write or derive the 4 equations of the HH model, and how to set the equations up for numerical integration using the forward Euler method. You should be able to explain why the voltage clamp is useful in studying ionic currents from an experimental point of view, and you should know the plotting convention for inward vs. outward currents. Know the names of the agents that block voltage dependent Na+ and K+ channels and the Na-K pump, and be able to
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Unformatted text preview: describe or draw their effects on the action potential (short and long term). Homework question: 1. In a voltage-clamp experiment, you clamp the membrane of an excitable neuron from an initial holding potential of -70 mV (where the cell has been resting for a long time) to the following 3 values in: -100 mV, -30 mV, +100 mV, and then back to –70 mV in each case after 2 ms. Assuming E K = -90 mV and E Na = +50 mV, plot the following semiquantitatively for each of the 3 experiments: current, leak current, capacitive current, sodium current, and potassium current, and total clamp current. This means the waveforms should be about right in their form, direction, duration, etc. If they are easily describable functions (like exponentials), then indicate by labelling with time constant. For full credit, label all axes legibly. Organize the responses in 3 columns labelled A, B, and C. CLAMPED AT -100mV CLAMPED AT -30mV CLAMPED AT +100mV...
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