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.