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Spontaneous Activity on Needle EMG 02

Topic: Physiology

Created on Friday, January 26 2007 by jdmiles

Last modified on Friday, January 26 2007.

Of the following, which pattern of spontaneous activity on EMG represents the firing of motor units (as opposed to muscle fibers)?

 
        A) Endplate spikes
 
        B) Enplate noise
 
        C) Complex repetitive discharges
 
        D) Myotonia
 
        E) Doublets
 

 


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This question was created on January 26, 2007 by jdmiles.
This question was last modified on January 26, 2007.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ANSWERS AND EXPLANATIONS




A) endplate spikes

This answer is incorrect.


Endplate spikes represent muscle fiber activity  (See References)

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B) enplate noise

This answer is incorrect.


Endplate noise represents miniature endplate potentials  (See References)

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C) complex repetitive discharges

This answer is incorrect.


Complex repetitive discharges (CRDs) represent spontaneous activity of multiple muscle fibers  (See References)

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D) myotonia

This answer is incorrect.


Myotonia represents muscle fiber activity  (See References)

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E) doublets

This answer is correct.


Doublets represent motor unit activity  (See References)

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References:

1. Preston, D.C., and Shapiro, B.E. (2005). Electromyography and Neuromuscular Disorders: Clinical-Electrophysiologic Correlations, 2nd Edition. Elsevier, Philadelphia.
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physiology
Spontaneous Activity on Needle EMG 02
Question ID: 0126070002
Question written by J. Douglas Miles, (C) 2006-2009, all rights reserved.
Created: 01/26/2007
Modified: 01/26/2007
Estimated Permutations: 12600

User Comments About This Question:

3 user entries
 

dzr3s
physiology Comment Feb 13, 2010 @ 19:01
More explanation please?


 

blondarb
physiology Re: Comment Feb 15, 2010 @ 11:14
I think Dr. Miles is simply noting that all the other choices are due to increased insertional activity. I assume the question is kind of a "which one of these things is not like the other". All the distractor answers describe classic insertional activity pattern which is typically caused by individual muscle fiber activity or release of Ach across the neuromuscular membrane. The only spontaneous motor unit activity you may see is a fasciculation. If you see a doublet/multiplet then it must be a motor unit firing. Looking at the wording of the question it may be slightly poorly worded.  Doug, am I wrong?


   

jdmiles
physiology Re: Re: Comment Apr 24, 2010 @ 11:45

Actually, all the choices represent some form of spontaneous activity.  The question is about the generator of said activity. 

Fasciculations, doublets, triplets, multiplets, myokymia, cramp potentials, neuromyotonic potentials, and the potentials of a resting tremor all represent electrical activity generated by one or more motor unit .  In all of those cases, the signal originates somewhere in or proximal to a motoneuron.  What we measure on EMG is the motor unit action potential.

Fibrillation potentials, positive sharp waves, and myotonic potentials are all generated by the muscle fiber itself.  What we measure are the action potentials of individual motor fibers.  Similarly, complex repetitive discharges (CRDs) are generated by individual muscle fibers linked by ephaptic coupling.  Endplate spikes are generated by the muscle fiber; although they are triggered by the distal twigs of motoneurons, they don't result in the firing of an entire motor unit.

A good reference for this is Preston & Shapiro's "Electromyography and Neuromuscular Disorders," 2nd Edition, chapter 14 (pages 199-213).

I hope this answers the question.  Please post again if it doesn't, or if you have more questions.  Thanks. 



 
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