Specialized glial cells called remove excess potassium ions from the extracellular fluid in the central nervous system.

The specialized glial cells that remove excess potassium ions from the extracellular fluid in the central nervous system are called Astrocytes.

Here are the steps of how they do it:

1. Astrocytes have a type of potassium channels on their membranes called inwardly rectifying potassium channels (Kir).

2. When the concentration of potassium ions increases in the extracellular fluid, these channels allow more potassium ions to enter the astrocyte.

3. Inside the astrocyte, potassium ions are dispersed in the large intracellular volume, which helps to decrease their concentration in the extracellular fluid.

4. Astrocytes can also move potassium ions to areas of lower concentration through a process called spatial buffering.

5. Finally, astrocytes can release the potassium ions back into the extracellular fluid when the concentration decreases, thus maintaining a balance.