Transcript ELECTRPHYSILOGY ACTION POTENTIAL

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

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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
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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
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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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