Explain the mechanisms responsible for the cell resting membrane potential (60% of marks) and describe the Gibbs Donnan effect (40% of marks)
A good answer included a definition of the resting membrane potential and a clear description of
the factors that determine it. Explanation of these factors should have included a detailed
description of the selective permeability of the membrane, electrochemical gradients and active
transport mechanisms. Answers should demonstrate awareness of the Nernst equation and the
Goldman-Hodgkin-Katz equation. These were often confused, sometimes with the GibbsDonnan
effect. Descriptions of the Gibbs-Donnan effect generally lacked detail and
understanding. The better answers included a definition and discussed in detail the influence of
non-diffusible ions (intracellular proteins) on the distribution of diffusible ions.
This is a topic which generally takes an entire book chapter to describe. What follows is an attempt to explain/describe the main concepts as briefly as possible while including the essential details.
Resting membrane potential: the voltage (charge) difference between the intracellular and extracellular fluid, when the cell is at rest (i.e not depolarised by an action potential).
Mechanisms responsible for the resting membrane potential:
Now, as for the Gibbs-Donnan effect:
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