Potassium channels are specialized proteins found in cell membranes that allow the selective passage of potassium ions (K+) in and out of cells. They play a crucial role in maintaining the cell's electrical balance and are essential for various physiological processes, including nerve impulse transmission and muscle contraction. These channels open and close in response to changes in voltage across the cell membrane, a process known as voltage gating. By regulating the flow of potassium ions, these channels help control the cell's resting membrane potential and contribute to the repolarization phase of action potentials in neurons and muscle cells.