Pumps move substances a concentration gradient, a process that requires energy. channels instead provide the means to move a substance a concentration gradient. neurons contain the following major types of channels: • channels that are always open, allowing continuous diffusion of a specific ion from a region of concentration to a region of concentration are leak channels. • channels that are normally closed that open in response to the binding of a are chemically gated channels. when open, they allow a specific ion to across the plasma membrane. • channels that are normally closed, but open in response to changes in across the plasma membrane are voltage-gated channels. when open, they allow a specific ion to diffuse across the membrane.