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Published byTyra Coker Modified about 1 year ago

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

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

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Membrane Potential in Response to Current Injection Outward Current Inward 0 0.5 nA Time mV -45 - -50 - -55 - -60 - -65 - -70 - -75 - Membrane potential Time

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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 - 80- 70- 50- 40 + 1 + 2 - 1 - 2 Outward Inward Slope dV/dI = R in

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Capacitive property of neural membrane Membrane potential Time Applied current Time

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

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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

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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

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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

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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

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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

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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

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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

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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

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

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

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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 )

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

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The Length Constant 37% 100% 0distance stimulation 100 10 1 0123401234

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Propagation of action potential The continuous conduction +50 0 - 60 + + + + + + + + + + + _ _ _ _ _ _ _ _ _ _ _ + + _ _ 123123 _ _ _ _ _ + + + + + + + + _ _ _ _ _ _ _ _ + + + + + + + + + + + + _ _ _ _ _ _ _ 123123 Direction of propagation +50 0 - 60

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Effect of myelination Increase membrane resistance Decrease membrane capacitance Less charge loss in charging capacitor and leakage across membrane, therefore increase the length constant.

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Propagation of action potential The saltatory conduction + + + _ _ _ + + _ _ _ _ _ _ + + +

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