Schémata a animace zpracovalo Servisní středisko pro e-learning na MU http://is.muni.cz/stech/ MEMBRANE OF EXCITABLE CELL ELECTRICAL TRANSMISSION OF INFORMATION ligand hydrophilic glycocalyx ion hydrophobic I – integral protein R – receptor E – enzyme K – channel P – pump (ATP-ase) Membrane molecules Protein molecules PLASMATIC MEMBRANE Nexus (gap junction) SODIUM-POTASSIUM PUMP 3 2 ATP ase Na+ K+ 150mM 155mM + + + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - Na+ K+ Concentration gradient Electrical gradient Nernst equation: Ex = R . T (Cxout) F (Cxin) ln ENa = +40 mV EK = -90 mV ECl = -70 mV ECa = +60 mV Ix = gx . (E - Ex) I – current, E – voltage, g – specific voltage and time-dependent conductance RESTING MEMBRANE VOLTAGE Er = -85 mV Equilibrium potential ACTION POTENTIAL Concentration gradient Electrical gradient + + + + + + - - - - - - - - - + + + + - - - - - - - - + + + + + + + - - - - - Na+ gNa K+ (E-EK) Depolarisation Transpolarisation Repolarisation (Hyperpolarisation) 50mV -100 -50 0 Threshold potential Resting potential transpolarisation depolarisation repolarisation influx of sodium eflux of potassium ACTION POTENTIAL hyperpolarisation •Unit of excitation activity •„All or nothing“ response •Propagation without decrement („domino effect“) •Refracterity Local current + depol. pol. Propagation with decrement Velocity of excitation propagation (depolarisation front) is a function of: •Intensity of local currents •Resistance outside the conductor (myelin) •Resistance of the conductor (indirect relationship) Nodes of Ranvier, saltatory conduction Neuron input section transmission section output section (coding of inf.) (transmission of inf.) (decoding of inf.) dendrites body ending synapses SYNAPSIS Synaptic vesicles (exocytose) Neurotransmitter (mediator) Presynaptic membrane Synaptic cleft Postsynaptic membrane (local change of voltage) Action potential Calcium ions •excitatory •inhibitory SYNAPSIS: A – axodendritic B – axosomatic C - axoaxonal A B C A actin myosin S. Silbernagl, A. Despopoulos: Color Atlas of Physiology • RESTING MEMBRANE POTENTIAL IS A CONDITION OF EXCITABILITY • IT DEPENDS ON HIGH RESTING MEMBRANE CONDUCTIVITY FOR POTASSIUM ACTION POTENTIAL IS A PROPAGATED ELECTRICAL SIGNAL GENERATED BY FAST SODIUM CURRENT INTO THE CELLx • ACTION POTENTIAL REPRESENTS UNIT OF INFORMATION • CODING OF INFORMATION IN THIS SYSTEM IS PERFORMED BY CHANGED FREQUENCY OF ACTION POTENTIALS