1. Action Potential in a Neuron. Rricketson 11.16.2012Copyright 2012 Seaspine. All rights reserved.1

2. THE MEMBRANE POTENTIAL-THE NA-K ATPASE PUMPThe Na+/K+-ATPase pump helps maintain membranepotential. Moves 3 sodium ions out and 2 potassium ions in, (removes 1 +charge) against concentration gradient Responsible for up to 2/3 of the neurons energy expenditure.2 3. THE MEMBRANE POTENTIAL-THE NA-K ATPASE PUMPMechanism (PDB ID 2B8E, 2ZKEbiological assembly) K+K+ Unphosphorylated form binds 3intracellular Na+ ions whilebinding ATP Hydrolysis of ATP ADP + Phosphorylation of the pump ata highly conserved Aspartateresidue; ADP + Pi. Phosphorylated form has a lowaffinity for Na+ Release Pump binds 2 extracellular K+ions Dephosphorylation. Dephosphorylation high affinityfor Na+ ions. K+ (2) ReleasedNa+K+ ions are transported into thecell.Na+ Na+ 3 4. THE MEMBRANE POTENTIAL-THE POTASSIUM CHANNELMechanism (PDB ID 2EKW,biological assembly)A neuron is permeable to K+Allows K+ to move from high[K+]o =5 mmolconcentration in the cytoplasm to low K+concentration in the extracellularenvironmentK+ Potassium diffuses out of the cellfrom its higher to lowerconcentration (chemical force). The Electrical potential or Vm= -90 mVelectrical force pulls K+ in to thecell. At equilibrium Vm= -90 mV The forces are equal and opposite K+ [K+]i =150 mmoK+ K+ 4 5. THE RESTING POTENTIALResting potential (EK )refers tothe difference between thevoltage inside and outside theneuron when not propagating anCl-impulse. The resting potential of K+the average neuron is around -70Na+mVT The inside of the cell is 70Na+mV less than the outside of the Na+cell.Na+ K+Na+K+ K+Cl-K+ 6. VOLTAGE GATED SODIUM CHANNEL (NAV)Voltage Gated Na Channel(PDB ID 2EKW, biological assembly) 6 helical segments. S1-S6 S4-Voltage Sensor 4 Arg + chargedresidues. Depolarization phase of AP Conformational change via linker S4-S5 P loops between S5 and S6 form pore - charged Glu and Asp line pore and attract Na+ ions. Inactivaton Gate (S5 and S6) closes pore (repolarization) Three states: Deactivated (closed) Activated (open) Inactivated (closed)- 6 7. GENERATING THE ACTION POTENTIALGenerated in axon hillock and Nodes ofRanvier of neurons by special types ofvoltage gated ion channels (Na+, Ca++)embedded in a cells plasma membrane Threshold is 55 mV for Na+ channel recruitment Amplitude is independent of the amount of current (all or nothing) Rising Phase: Rapid influx of Na+ causes a: Depolarization of membranepotential Inactivation of Na+ channels (ENa+55 mV) Falling Phase: K+ channel activation(repolarization) Afterhyperpolarization K+ channels slow to close 7 8. VOLTAGE GATED SODIUM CHANNEL (NAV)Interactive walk-through of the Action Potential.8 9. THANK YOU9