A researcher is analyzing the distribution of ion channels in the nervous system. He finds that a type of ion channel is a lot more abundant in the neurons than in the glial cells. What can you conclude about this ion channel?

I. It is a lot faster than G protein-coupled receptor (GPCR)

II. It responds to changes in voltage

III. It is involved in depolarization

G protein-coupled receptor is an example of __________ ion channel and the insulin receptor is an example of __________ ion channel.

Which of the following is true regarding ligand-gated ion channels?