Thankfully, the sodium-potassium pump isn't the only way in or out of the cell – the membrane is also riddled with ion channels, large proteins that can provide safe passage across the membrane, when their respective gates are open. What are ion channels?
1) Proteins that allow the passage of ions across the cell membrane
2) Proteins that pump sodium and potassium ions in and out of the cell
3) Proteins that regulate the opening and closing of ion channels
4) Proteins that transport ions across the cell membrane
