Last update: Dec 2nd, 2017

Distribution of Ions In Resting Axons

• The ion concentrations in the extracellular fluid (ECF) and intracellular fluid (ICF) of a resting axon can be measured.

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These concentrations are often expressed in millimolar (mM) units.

Molarity:

• Molarity (M) is the number of moles of a solute in one liter of solution.
• One Mole of a solute contains 6.023 x 1023 particles.
• Thus, a 1 molar (M) solution contains 6.023 x 1023 particles in a liter of solution.
• A 1 millimolar (mM) solution is 1000 X less concentrated than a 1 M solution.

• These measurements show that Na+ (sodium) and Cl- (chloride) are concentrated in the ECF.

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• In contrast, K+ (potassium) and proteins- (organic anions) are concentrated in the ICF.

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