Question

What happens to the membrane potential when a neuron is placed in a solution that is high in K+? Why does this occur?

Answer 1

ANSWER: Increase in the extracellular potassium results in the following effects:

The normally present hyperpolarising outflow of the potassium ions will be slowed down. Less hyperpolarising outflow is equivalent to depolarisation, since there is depolarising inflow of sodium that was also not slowed down by an equivalent increase in the intracellular sodium. This results in the change in equilibrium potential of the cell.

The increase in the membrane potential opens up the sodium channels, which lets in more sodium into the cell causing to depolarise the cell more.

The slow depolarisation causes partial sodium channel inactivation to haplen as well. This prevents the neuron from triggering a full action potential. As a result the cell remains in the slightly depolarised state but never fires.