Summary Neuroscience; The Nernst Equation Review

The Nernst equation
The transport equation can be narrowed down to an equation called the Nernst equation.
As ions move across the membrane, they affect the potential difference due to a change in
ions (which affects +ve/-ne concentration). The Nernst equation is as followed:


RT [X]o
EX = ln
zF [X]i
R = 8.315 V C K-1mol-1 (Ideal gas constant)
T = K (Absolute temperature, kelvin)
Z = Charge of an ion (Valence) If you have a negative ion flip the final fraction
F = 96,500 C mol-1 (Faraday’s constant)
[X]o = Ionic concentration outside the cell
[X]I = Ionic concentration inside the cell
Ex = Ionic equilibrium potential




The Nernst equation can be further simplified to the followed:


[X]o
E X = 61.5 log10
[X]i
At Ek there is a balance between the concentration gradient that forces K + to move from left
to right through a membrane. The resulting negative charge on the left of the membrane
and positive charge on the right of the membrane that holds K+ inside the cell. The potential
at which these 2 forces balance is the reversal potential the potential at which there is no
net movement of K+ across the membrane. Ek is the potential at which there is no net
movement of potassium across the membrane – this is the reversal potential for that
particular ion. The reversal potential is the logarithm of the ratio of the outside vs the
inside.