Resting membrane Potential (RMP)
Electrical potential of cell at rest. Above example is cardiac muscle tissue.
The five – phase process characterized by the movement of K+, Na, and Ca++( primarily) across cell membrane.
Threshold potential (TP)
The point at which a stimulus will initiate a response helps determine Automaticity of pacemaker cells.
Depolarization–fast NA+ channels open–Na+ rushes in to replace “lost” positive charges.
Overshoot–rush of positive Na+ ions causes polarity to be positive for a short time.
Plateau Phase–Na channels close, K= channels decrease permeability, slow Ca++ channels open–Ca++ goes into cell, Ca++ maintains cell in depolarized state for a prolonged period of time.
(Verapamil works here)
Repolarization — rapid loss of K+ ions restores and
electrogenic pump RMP to 90 mV.
Polarized (resting) Cell–negative polarity inside slowly K+ leaves IC space (concentration gradient). Decreasing RMP to TP (Note; in SA node, CA++ influx responsible for decay of RMP to TP) K+—Electrolyte most likely to affect electrophysiology.
Resting Membrane Potential (RMP)
SA Node -50 to -60 mV
AV Node -65 to -70 mV
Muscle – 90 to – 100 mV
Threshold Potential (TP)
SA Node – 40 mV
AV Node -55 to – 60 mV
Muscle – 60 mV