How is the resting membrane potential established?

Question

What will be an ideal response?

Answer 1

Resting potential arises from the distribution of charged proteins and small ions.

First, the cytoplasm of a neuron at rest has more negatively charged proteins than the extracellular fluid. Being large and charged, these proteins cannot diffuse across the lipid bilayer of the cell membrane. Therefore, the proteins contribute to the negative charge inside the neuron.

Secondly, positively charged potassium ions (K+) and positively charged sodium ions (Na+) also influence resting potential. Sodium ions cannot cross a resting neuron's membrane, but potassium ions can (through passive transport proteins).

Sodium and potassium are actively moved across the neuron membrane by a sodium-potassium pump. The transport proteins pump out three sodium ions and pump in two potassium ions. This sets up concentration gradients across the cell membrane. Since sodium cannot freely move into the neuron, there is a steep gradient set up across the membrane. The pumping out of positively charge sodium also makes the cytoplasm even more negatively charged.

Since potassium ions can freely cross the membrane, some potassium ions leave the cell through passive transport proteins in the membrane. They move along their concentration gradient, since the levels are higher in the cytoplasm due to the sodium-potassium pump. Movement of potassium out of the cell further increases the charge difference across the membrane, making the cytoplasm even more negative.