1
MEMBRANE OF EXCITABLE CELL.
ELECTRICAL TRANSMISSION OF
INFORMATION.
Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
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ligand
hydrophilic
glycocalyx ion
hydrophobic
I – integral protein
R – receptor
E – enzyme
K – channel (kanál)
P – pump (ATP-ase)
Membrane
molecules
Protein molecules
PLASMATIC MEMBRANE
Nexus (gap junction)
Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University3
SODIUM-
POTASSIUM
EXCHANGER
Marie Nováková
Department of Physiology
Faculty of Medicine, Masaryk University
4
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
Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University5
ACTION POTENTIAL
Concentration gradient
Electrical gradient
+ + + + + + - - - - - - - - - + + + +
- - - - - - - - + + + + + + + - - - - -
Na+
gNa
K+
(E-EK)
Depolarisation
Transpolarisation
Repolarisation
(Hyperpolarisation)
Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University6
Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University7
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
Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
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Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University9
• 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
Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University10
• ACTION POTENTIAL REPRESENTS UNIT OF
INFORMATION
• CODING OF INFORMATION IN THIS SYSTEM IS
PERFORMED BY CHANGED FREQUENCY OF
ACTION POTENTIALS