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# More problems.pdf

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McGill University

Physiology

PHGY 311

Ellis Cooper

Fall

Description

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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