Recording of Membrane Potential

1
Recording of Membrane Potential
Electrotonic potential
2
Local Electrical Circuit
Stimulation
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Membrane Potential in Response to Current
Injection
mV -45 - -50 - -55 - -60 - -65 - -70 - -75 -
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Current-Voltage (I-V) Relationship
DV I x Rin
Rin (input resistance) can be defined by slope of
the I-V curve. The I-V curve shown here is
linear Vm changes by 10 mV for every 1 nA change
in current, yielding a resistance of 10 mV/1nA,
or 10 x 106W.
5
Capacitive property of neural membrane
Membrane potential
Time
Applied current
Time
6
Current flow across the neural membraneionic and
capacitive current
Capacitive current
Ionic current
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K
K
K
Na
K
Na
Na



7
Electrical equivalent circuit for examining the
effects of membrane capacitance
8
Electrical equivalent circuit for examining the
effects of membrane capacitance
Extracellular side
Im
RESTING STATE No current flow through capacitor
or resistor.
9
Electrical equivalent circuit for examining the
effects of membrane capacitance
Extracellular side
Im
- -
INITIAL STEP V 0 and no current flow through
the resistor. Im Ic
10
Electrical equivalent circuit for examining the
effects of membrane capacitance
Im
Vm increase and drive the current to flow through
the resistor. Im Ii Ic
11
Electrical equivalent circuit for examining the
effects of membrane capacitance
Im
Vm increase and drive the current to flow through
the resistor. Im Ii Ic
12
Electrical equivalent circuit for examining the
effects of membrane capacitance
Im
Capacitor is fully charged and no more current
flow through capacitor. The system approach
steady state and all current flow through the
resistor. Im Ii
13
Electrical equivalent circuit for examining the
effects of membrane capacitance
Extracellular side
Im
- -
Current generator
Cin
Rin
Cytoplasmic side
The process is reversed after no current is
applied.
14
Membrane capacitance and time course of potential
change
Out
Im
Ii
Membrane current (Im)
Ionic current (Ii)
Ic
0
In
Capacitive current (Ic)
15
Neuronal process as a co-axial fiber
Current Generator
RECF
Rm
Ra
16
Neuronal process as a co-axial fiber
Inner layer insulation(membrane)
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Neuronal process as a co-axial fiber
Extracellular fluid (outer conductor)
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Neuronal process as a co-axial fiber
Current Generator
Rm
Ra
19
The Length Constant
20
Propagation of action potentialThe continuous
conduction
50 0 - 60
Direction of propagation
50 0 - 60
21
Effect of myelination

• Increase membrane resistance
• Decrease membrane capacitance

Less charge loss in charging capacitor and
leakage across membrane, therefore increase the
length constant.
22
Propagation of action potentialThe saltatory
conduction
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