In its resting state, which ions can cross the membrane of a neuron?

1. A cell membrane is semipermeable, meaning only some ion types can cross it. 2. At rest it lets potassium and chloride ions through but blocks sodium ions. 3. Diffusion of those two permitted species builds the charge layers on either face of the membrane. 4. The Coulomb force then halts further transfer, leaving a steady voltage across the membrane. 5. Sodium permeability appears only when a stimulus changes the membrane, which is a later stage. _Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section Nerve Conduction_