The nervous system of a new organism is characterized by Nernst potentials and p
ID: 705030 • Letter: T
Question
The nervous system of a new organism is characterized by Nernst potentials and permeabilities to particular ions. The data is summarized in the photo attached:
a) Is there any net flow of ions at the resting potential in part ‘b’ above? Why or why not?
b) 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.
c) 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 -50 mV 20 mV Permeability 1 0.05 2+ Li*Explanation / Answer
a) If we consider that the resting potential of a neuron is -70 mV, then as per the data presented, the equilibrium potentials of both Mg2+ and Li+ are higher than the resting potential. As a result there will be a net ion flow inside the cell.
b) The equilibrium potential of an ion is given by the Nernst equation:
Eion = RT/zF * log[ion]out/[ion]in
where R = gas constant; T = temperature; z = ion charge; F = faraday constant
[ion]out = ion concentration outside membrane
[ion]in = ion concentration inside
The membrane potential corresponding to K+ and Mg2+ ions are:
E(K+) = RT/(+1)(F)*log[K+]out/[K+]in ----------------(1)
E(Mg2+) = RT/(+2)(F)*log[Mg2+]out/[Mg2+]in ------------(2)
It is given that E(Mg2+) = -50 mV and the concentrations of both the ions inside and out are the same. Therefore, based on equation (1) divided by (2) we can write:
E(K+) /(-50 mV) = 2/1
E(K+) = 2 *(-50 mV) = -100 mV
c) Given:
Resting potential of neuron - -40 mV
Poial applied = 25 mV
In this case, depolarization causes the inside of the membrane to become less negative : -40 + 25 = - 15 mV
New membrane potential is - 15 mV
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