Rapid changes in membrane potential that spread rapidly along nerve fiber membrane. Resting: initial state, -90 mv - depolarization: sudden permeability to na+, neutralizes -90 mv - repolarization: na+ channels close, k+ channels open more, rapid k+ diffusion to exterior reestablishes -90 mv - voltage-gated na+ channel: 2 gates, 1 near the outside (activation, closed @ -90 mv open @ -70~-50 mv increase permeability 500~5000x times) 1 near the inside (inactivation, closes @ -70~-50 mv 0.001 seconds later, opens @ -90 mv) - voltage clamp 2 electrodes inserted into nerve fiber - 1 for voltage of membrane potential and 1 for conducting electrical current into/out of nerve fiber. potential increased from -90 -> 0, voltage-gated na/k channels opened. to counterbalance na/k transport, current injected automatically to maintain 0 mv (current must be equal but opposite polarity to net current flow)
