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Excitable Cells - Lecture 5 (13/02/2018)
Ionic Basis of the Membrane Potential
If there is a hole in a membrane which is separating two solutions of glucose, one high concentration and one low concentration, then we'll get glucose moving from one compartment to the other via diffusion.
In this method only the concentration gradient determines the direction of movement.
(The Cell interior is -70 mV negatively charged with respect to outside.)
However it needs to be stated that in addition to concentration gradient, the electric gradient also has to be accounted when calculating the diffusion pathway of ions.
The interior of cells is generally negative as there are a large quantity of negatively charged proteins which are fixed inside the cell that balance out the negative and positive ions across the membrane.
Hence both the Concentration gradient and the Electric gradient influence which direction the ions travel across the membrane.
So as seen above the direction of movement of K + and Cl- cannot be estimated by solely focusing on the concentration gradient.
For example, by using the example of K+, the concentration gradient is trying to move potassium out of the cell but the electrochemical gradient is trying to hold it inside the cell,
so movement of ions cannot be predicted using only its concentrations.
In order to calculate the direction and energy due to the electrical and concentration gradients mathematical equations must be applied.
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