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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
• RESTING MEMBRANE POTENTIAL IS A CONDITION
OF EXCITABILITY
• IT DEPENDS ON HIGH RESTING MEMBRANE
CONDUCTIVITY FOR POTASSIUM
ACTION POTENTIAL
Concentration gradient
Electrical gradient
+ + + + + + - - - - - - - - - + + + +
- - - - - - - - + + + + + + + - - - - -
Na+
gNa
K+
(E-EK)
Depolarisation
Transpolarisation
Repolarisation
(Hyperpolarisation)
ACTION POTENTIAL IS A PROPAGATED
ELECTRICAL SIGNAL GENERATED BY FAST
SODIUM CURRENT INTO THE CELL
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
MUSCLE: striated, heart, smooth
MYOFIBRILE
T-canalSR
sarcolemma
mitochondrion
actin
myosin