What are the roles of channels in cell membranes? What different types of channels exist and why are the different types important?

Channel proteins are  pores (or tunnels) that enable ions to diffuse through the cell membrane into or out of the cell. Some channels are open all the time, allowing continuous free movement. Others are gated, meaning that movement through them is controlled. This is important in physiological functions such as the action potential used by nerves to transmit information. In nerves, it is the gated sodium and potassium channels that are most important. Each ion has its own channel through which it passes - there are separate Na and K channels in the membrane. Thse ions can't pass directly through the membrane because of its lipid core.