1) Question 2 (8 pts) You discover a new organism living at the bottom of a cave
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1)Question 2 (8 pts) You discover a new organism living at the bottom of a cave. You characterize its nervous system by the Nernst potentials and permeabilities to particular ions. The data is summarized in the table below.
Equilibrium Potential
Permeability
Mg2+
-50 mV
1
Li+
20 mV
0.05
a.(2 pt) How would you expect the resting potential to change if the permeability to Li+ was tripled (more positive, more negative, no large change). Explain your answer.
a.(1 pt) You add a drug that blocks Mg+2 channels and causes the permeability of Mg+2 to decrease to 0. What is the new resting potential of the neuron.
b.(2 pt) Is there any net flow of ions at the resting potential in part ‘b’ above? Why or why not?
c.(2 pt) You discover that there are also K+ ions present at the same intracellular and extracellular concentrations as the Mg+2 ions (although there are no channels for the K+ ions to pass through). What is the Nernst potential of K+? Explain your thinking.
d.(1 pt) Assume that the resting potential of the neuron is -40 mV. You are conducting a voltage clamp experiment, and decide to depolarize the membrane by 25 mV. What is the new membrane potential?
Equilibrium Potential
Permeability
Mg2+
-50 mV
1
Li+
20 mV
0.05
Explanation / Answer
Resting potential will become more positive because of Lithium ion concentration increase. Lithium is positively charged so positive contribution will be more.
New resting potential will be -20 mv.
In resting potential there will not be any ion exchange.
K+ ion potential =70mv
New membrane potential = 40-25 mv= 15mv
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