Q2. (20 pts) Consider an axon in which ALL voltage-gated ion channels have beern
ID: 202752 • Letter: Q
Question
Q2. (20 pts) Consider an axon in which ALL voltage-gated ion channels have beern BLOCKED, so that the axon membrane only contains leak conductance and capacitance Now, we patch into the axon and provide a step voltage command to +30mV. The graph below shows the time course of voltage change at a point 50 microas away from where the voltage command is applied. +30 mV -20 mV Tau 70 mV Time A) What determines the value of Tau (T)? (4 pts) voltage command? (8 pts) C) Draw a curve on the graph above to indicate the voltage change over time at a point only 25 microns away from the voltage command point. Indicate (approximately and qualitatively) the Tau, the maximum voltage achieved, and why, if at all, these values differ from those for the membrane at 50 microns away. (8 pts)Explanation / Answer
a. At first the nerve cell had a resting potential of -70 mV. Once the voltage is applied, a small number of Na+ channels get depolarize and open up at a threshold level due to increased voltage, that cause this transition shown by Tau.
b. Voltage rise to a steady rate at -20 mV only because When a definite membrane potential depolarization level is reached, the membrane potential depolarize rapidly to reach equilibrium state from a resting state. When few voltage dependent Na+ channels open, they cause more Na+ channels to open and depolarize. At this point, the membrane potential gradient has found its Na+ equilibrium by sodium pump at -20mV voltage so it has become steady at this point however +30mV is given.
c. No changes will be there as these values will not change because the membrane resting potential, threshold and equilibrium state all will remain the same at any voltage applied.
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