lon Channels Exterior Na Na Na ++++ Resting membrane potential 刘 Cytosol K' Resting Voltage-gated Ligand-gated Signal-gated channel- channel-opens channel-opens channel- always open一 (transiently) in response -or-opens or in response to to a specific closes in change in the extracellular response to membrane signal a specific potential intracellular molecule Ion Channels -or-