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McGill University
PHGY 311
Ellis Cooper

Question 1: The two graphs below are results from a voltage clamp experiment and show: 1) the I-V curve for the peak voltage-gate Na current and the K current; and 2) the time for recovery of inactivation for the peak Na current, measured at -75 mV. a) What is the threshold for this neuron? (Be as accurate as possible.) b) What is the absolute refractory period? (Assume no change in K conductance from rest.) c) If a stimulus activates a 80 nS chloride conductance at rest, what is the new threshold at rest (assume that E = -ClmV). Explain how you arrived at all your answers. I-V Curve for peak Na and K currents nA 2 IK mV -100 -80 -60 -40 -20 20 40 60 80 100 -2 -4 -6 INa -8 -10 100 80 60 40 % of Maximum Recovery from Inactivation 0 0 5 10 15 20 25 30 35 40 45 50 TIME (ms) Question 2 This neuron has a resting G = 16 nS, a resting G = 2nS and G = 0. The resting V = - K - Na Cl m 70mV and E = K85 mV, E Na= +50 mV and Cl is passively distributed. The Table gives the results from a voltage-clamp experiment on this neuron. The left column is the membrane potential of the voltage step and the right column is the corresponding peak Na current. A) Plot the I-V for the peak Na current and for the K current (assume that G K remains constant at its resting value). B) Using the data from the voltage-clamp experiment, what is the maximum G Na for this
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