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Recording of Membrane Potential Recording oscilloscope Nerve cell Stimulating electrode + 60 - + 30 - 0 - - 30 - - 60 - - 90 - Oscilloscope display mV.

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Presentation on theme: "Recording of Membrane Potential Recording oscilloscope Nerve cell Stimulating electrode + 60 - + 30 - 0 - - 30 - - 60 - - 90 - Oscilloscope display mV."— Presentation transcript:

1 Recording of Membrane Potential Recording oscilloscope Nerve cell Stimulating electrode Oscilloscope display mV Insert electrode Resting potential Electrotonic potential

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

3 Membrane Potential in Response to Current Injection Outward Current Inward nA Time mV Membrane potential Time

4 Current-Voltage (I-V) Relationship  V=I x R in R in (input resistance) can be defined by slope of the I-V curve. The I-V curve shown here is linear; V m changes by 10 mV for every 1 nA change in current, yielding a resistance of 10 mV/1nA, or 10 x 10 6  I (nA) HyperpolarizationDepolarization Outward Inward Slope dV/dI = R in

5 Capacitive property of neural membrane Membrane potential Time Applied current Time

6 Current flow across the neural membrane ionic and capacitive current KKNa K K Ionic current Capacitive current

7 Electrical equivalent circuit for examining the effects of membrane capacitance R in _ Current generator Cytoplasmic side Extracellular side + CmCm ImIm IiIi IcIc Ionic current Capacitive current

8 Electrical equivalent circuit for examining the effects of membrane capacitance Extracellular side R in Current generator Cytoplasmic side C in RESTING STATE: No current flow through capacitor or resistor. ImIm IiIi IcIc

9 Electrical equivalent circuit for examining the effects of membrane capacitance - + Extracellular side R in Current generator Cytoplasmic side C in INITIAL STEP: V = 0 and no current flow through the resistor. I m = I c ImIm IiIi IcIc

10 Electrical equivalent circuit for examining the effects of membrane capacitance V m increase and drive the current to flow through the resistor. I m = I i + I c ImIm IiIi IcIc - + Extracellular side R in Current generator Cytoplasmic side C in

11 Electrical equivalent circuit for examining the effects of membrane capacitance - + Extracellular side R in Current generator Cytoplasmic side C in V m increase and drive the current to flow through the resistor. I m = I i + I c ImIm IiIi IcIc

12 Electrical equivalent circuit for examining the effects of membrane capacitance - + Extracellular side R in Current generator Cytoplasmic side C in Capacitor is fully charged and no more current flow through capacitor. The system approach steady state and all current flow through the resistor. I m = I i ImIm IiIi IcIc

13 Electrical equivalent circuit for examining the effects of membrane capacitance - + Extracellular side R in Current generator Cytoplasmic side C in The process is reversed after no current is applied. ImIm IiIi IcIc

14 Membrane capacitance and time course of potential change Membrane potential (  V m ) 63% Time constant (  ) a b Membrane current (I m ) IcIc IiIi Ionic current (I i ) Capacitive current (I c ) ImIm Out In 0

15 Neuronal process as a co-axial fiber Current Generator RaRa RmRm R ECF

16 Neuronal process as a co-axial fiber Inner layer insulation (membrane) Inner conductor (cytoplasm) Outer conductor (ECF) Outer layer insulation (ECF) Cytoplasm Membrane

17 Neuronal process as a co-axial fiber Extracellular fluid (outer conductor) rmrm cmcm rara Cytoplasm (inner conductor) Membrane Tranmembrane resistance (r m ) Axial resistance (r a ) Outer resistance (r aECF )

18 Neuronal process as a co-axial fiber Current Generator RaRa RmRm

19 The Length Constant 37% 100% 0distance stimulation

20 Propagation of action potential The continuous conduction _ _ _ _ _ _ _ _ _ _ _ + + _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Direction of propagation

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 _ _ _ + + _ _ _ _ _ _ + + +


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