Check out this Cartoon on how your thyroid works. Thyroid issues can get complicated, so this might help explain a little bit better what dotors do not explain to their patients. Check out that T-shirt here:
This diagram shows how sodium and potassium ions are pumped through protein channels. The sodium ions are pumped out of the cell, while potassium is pumped into the cell. The movement of these ions creates resting potential and action potential.