1. Recording of Membrane Potential
+ 60 -
+ 30 -
0 -
- 30 -
- 60 -
- 90 -
Oscilloscope display mV
Insert electrode
Resting potential
Recording oscilloscope
Nerve cell
Stimulating electrode
Electrotonic potential

2. Local Electrical Circuit
Stimulation +
The resting membrane potential
Intracellular axial resistance
Membrane capacitance +

3. Membrane Potential in Response to Current InjectionmV
-45 -
-50 -
-55 -
-60 -
-65 -
-70 -
-75 -
Outward
Current
Inward
0.5 nA
Time
Membrane potential
Time

4. Current-Voltage (I-V) Relationship
I (nA)
Hyperpolarization Depolarization
+ 1
+ 2
- 1
- 2
Outward
Inward
Slope dV/dI = Rin
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 membrane ionic and capacitive current
Ionic current - - - K Na K Na K Na K + + +

7. Electrical equivalent circuit for examining the effects of membrane capacitance
Rin
_ _
Current generator
Cytoplasmic side
Extracellular side
+ + Cm
Ionic current
Capacitive current Ic Ii Im

8. Electrical equivalent circuit for examining the effects of membrane capacitance
Extracellular side Im
Rin
Current generator
Cytoplasmic side
Cin Ic Ii
RESTING STATE: No current flow through capacitor or resistor.

9. Electrical equivalent circuit for examining the effects of membrane capacitance
Extracellular side Im
Rin
Current generator
Cytoplasmic side
Cin Ic
- -
+ + Ii
INITIAL STEP: V = 0 and no current flow through the resistor. Im = Ic

10. Electrical equivalent circuit for examining the effects of membrane capacitance
- -
+ +
Extracellular side
Rin
Current generator
Cytoplasmic side
Cin Im Ic Ii
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
- -
+ +
Extracellular side
Rin
Current generator
Cytoplasmic side
Cin Im Ic Ii
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
- -
+ +
Extracellular side
Rin
Current generator
Cytoplasmic side
Cin Im Ic Ii
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 Ic
Current generator
- -
+ +
Rin
Cin Ii
Cytoplasmic side
The process is reversed after no current is applied.

14. Membrane capacitance and time course of potential change
Membrane potential (D Vm)
63%
Time constant (t) a b
Out Im
Membrane current (Im) Ii
Ionic current (Ii) Ic 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 conductor (cytoplasm)
Outer conductor (ECF)
Outer layer insulation (ECF)
Inner layer insulation (membrane)
Cytoplasm
Membrane

17. Neuronal process as a co-axial fiber
Membrane
Tranmembrane resistance (rm)
Axial resistance (ra)
Outer resistance (raECF)
Extracellular fluid (outer conductor) rm cm ra
Cytoplasm (inner conductor)
Membrane

18. Neuronal process as a co-axial fiber
Current Generator Rm Ra

19. The Length Constant 100% 100 10 37% 1 l 0 distance 0 1 2 3 4
stimulation
100 10 1

20. Propagation of action potential The continuous conduction
+50
- 60
Direction of propagation
+50
- 60
_ _ _ _ _ _ _ _ _ _ _
_ _ _ _
1 2 3
_ _ _ _ _
+ + +
_ _ _
_ _ _ _ _
_ _ _ _ _ _ _ _ _ _ _ _ _ _
1 2 3

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 potential The saltatory conduction
_ _ _ _
+ + +
_ _ _ _
+ + +
_ _ _