Basic Electrophysiology for Electrotherapy

Nan-Ying Yu Mar.4.2008

Textbook: Robinson, Andrew J., & Snyder-Mackler, Lynn, Clinical electrophysiology: electrotherapy and electrophysiologic

testing, Williams & Wilkins, pp.83-119, 1995.

Electrical Excitability of Muscle and Nerve

Resting membrane potential

-90 mV for muscle fibers

-75 mV for peripheral nerve fibers Action potentials (depolarization/

repolarization/ hyperpolarization) “all or none” in character

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Action Potential Propagation

Two most important passive electrical properties with respect to the transmission of ion currents in nerve and muscles are the membrane resistance (rm) and the internal (intracellular) resistance (ri)

Small-diameter fibers have relative high internal resistance as compared to large-diameter fibers

The higher the ri the slower the propagation speed 3

Experiment Setup for Examining AP Propagation

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Orthodromic v.s. Antidromic Propagation(Physiologic)

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Classification of Peripheral Nerve

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Factors influencing muscle force production Frequency of Activation Number of Fibers Activated

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Frequency of Activation v.s. Number of Fibers Activated

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Control of Force Generation in Volitional Contraction

“size principle” (recruitment)

S FR FF“rate coding” (discharge frequency)

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Volitional Contraction

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Activation of excitable tissues with electrical stimulation

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Stimulus characteristics for activation of excitable tissues

strength-duration curve

rheobase

chronaxie

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S-D curves

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Diagrammatic representation for the result of S-D curves in different excitable tissues

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Clinical responses to nerve and muscle stimulation

Sensory-Level Stimulation Motor-Level Stimulation Noxious-Level Stimulation

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Clinical responses to nerve and muscle stimulation

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Sensory-Level Stimulation

Frequency set 1 to 5 pps “Tapping” sensation

Frequency >15 gradual diminution in the ability to sense the stimulation (adaptation)

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Motor-Level Stimulation Compared to volitional recruitment, recruitment order in ES tends to

be reversed.

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