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Basic Electrophysiology forElectrotherapy

Nan-Ying YuMar.4.2008

Textbook: Robinson, Andrew J., & Snyder-Mackler, Lynn,

Clinical electrophysiology: electrotherapy and electrophysiologic

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

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Electrical Excitability of Muscle andNerve

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 currentsin 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

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Experiment Setup for ExaminingAP 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 forceproduction

Frequency of Activation Number ofFibers Activated

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Frequency ofActivation

v.s.Number ofFibers Activated

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Control ofForce Generation inVolitional 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 withelectrical stimulation

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Stimulus characteristics for activationof excitable tissues

strength-duration curve

rheobase

chronaxie

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S-D curves

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

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Clinical responses to nerve andmuscle stimulation

Sensory-Level Stimulation

Motor-Level Stimulation

Noxious-Level Stimulation

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Clinical responses to nerve andmuscle 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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