This is a longwinded question but it is easy to follow along

This is a long-winded question but it is easy to follow along if you know the basics of Nernst potentials.

Lets say there is a negatively charged ion A-.

The concentration of A- outside of the neuron is greater than the concentration of A- inside the neuron.

The Nersnt potential of this ion is -50mV.

The resting membrane potential of the neuron is -70mV.

Will increasing the permeability of the ion cause a depolarization or a hyperpolorization.

I am confused because there are two viable solutions here. Either increasing the permeability will lead to more negative ions entering the cell causing a hyperpolarization. Or because increasing the permeability of the ion causes the cells potential to go more towards the Nernst potential of the ion the cells potential will go from -70mV towards -50mV causing a depolarization. Which is it?

Solution

A neuron is said to be polarized when there is difference in +ve and -ve charge of electric potential across the membrane. Generally an axon shows high potassium, low Na+,Cl- internally and outside axon low potassium and high Na+ , Cl- could be seen. Equilibrium of an ion could be finding using the Nernst equation. Through Nernst equation it is possible to calculate the electrical charge required to balance the concentration of an ion across the membrane which results in equilibrium potential. When the Na+ permeability across the membrane, if gets increased, the equilibrium potential for the Na+ gets unchanged. Depolarization results due to increased of K+ concentration outside the membrane in the resting membrane potential. Hyperpolarization is opposite to depolarization, as it results in efflux of K+ or influx of cl- ions across the membrane. Whereas hyperpolarization gets inhibited due to influx of Na+ ions across the membrane through sodium gated channels. At resting potential, the Na+ influx into membrane is zero with a resting potential of -70mV.