Term
| What is a motor unit? What is the start and end? |
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Definition
| A nerve and all the muscle fibers it innervates. Includes the anterior horn cell as well as the neuromuscular junction. |
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Term
| How many muscle fibers can a single axon of a motor unit innervate? |
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Definition
| Highly variable. 1-8 in intrinsic eye muscles. 2000 in the gastrocnemius. |
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Term
| What is the electrical signal of a muscle at rest? |
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Definition
| No signal, muscle is quiescent at rest. - flat baseline. |
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Term
| At what point is electromyography used to measure muscle? |
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Definition
when muscle is at rest
during minimal contraction
during maximal contraction |
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Term
| What are the three electrodes in electromyography? |
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Definition
Reference electrode on skin surface
Recording electrode inserted into muscle (extracellular!)
A ground to minimize interference |
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Term
| What does minimal contraction produce normally? |
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Definition
| A single Motor Unit Potential (MUP). Appears as a triphasic wave (usually - normal can also be 2 or 4). Preceise motor skills |
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Term
| Increased force contraction produces what normally? |
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Definition
| Increase in firing rate of the motor unit. Next, a greater number of MUPs become active - normal recruitment. Alteranation of different MU's prevents fatigue. |
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Term
| Where is the ground electrode placed? |
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Definition
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Term
| What is the time between stimulation and the recording of the CMAP (compound muscle action potential with multiple motor units). |
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Definition
| Distal or proximal latency as appropriate. |
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Term
| An elbow stimulis will activate what nerve? |
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Definition
| Median nerve, pickup is still from the median innervated thenar muscles. A forearm stimulation only activates thenar muscles while the elbow stimulation activates all muscles innervated by the median nerve. |
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Term
| What is the time for satlatory conduction between the elbow and the wrist. The wrist and the thumb? |
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Definition
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Term
| How is conduction velocity calculated? |
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Definition
Distance from elbow to wrist divided by (latency of elbow to thenar muscles minus latency from wrist to thenar muscles).
Must use elbow to thenar muscle distance (once you hit thenar muscle, signal slows). |
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Term
What is Nerve Degeneration (Wallerian Degeneration)?
What are the subtypes? |
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Definition
Axonal death.
Two types: degeneration of all axons, degeneration of some axons in the nerve.
IN EITHER DEGENERATION, FIBRILLATIONS WILL BE SEEN AT REST (continue with total denervation). |
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Term
| What happens to the potential in partial denervation? |
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Definition
| Polyphasic potentials develop after 1-2 months. Parent axon has developed peripheral sprouts which are smaller and less myelinated that original branches. Original branches contract first, followed by new ones - polyphasic! |
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Term
| What does partial denervation mean? |
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Definition
| some muscle fibers lose innervation. |
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Term
| What happens 2-3 weeks after Wallerian degeneration in minimal contraction? |
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Definition
| Muscle fibers lose all neuronal control 2-3 weeks after Wallerian degeneration (at this point they are denervated). |
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Term
| What happens 2-3 weeks after partial denervation in minimal contraction? |
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Definition
| The axon dies. Line of normal motor unit that is still functioning is a normal phasic. |
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Term
| What happens 6-8 weeks after denervation in minimal contraction? |
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Definition
| Small poorly myelinated peripheral branches are given off by the normal motor unit nearby. There is a polyphasic motor unit potential. |
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Term
| What happens with total denervation of muscle and minimal contraction? |
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Definition
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Term
| What happens with total denervation and maximal contraction? |
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Definition
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Term
| What happens with partial denervation and maximal contractions? |
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Definition
| There is decreased recruitment and repeat firing of the same motor unit over and over. Continues as long as there is partial denervation - results in fatigue! |
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Term
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Definition
| Speed of conduction and amplitude of response (R) from the stimulation (S) points along the extremity are all normal. |
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Term
Conduction in Wallerian (axonal) degeneration = axonal death
if
(a) All axons are degenerated
(b) Some axons are degenerated |
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Definition
If all axons are degeneraed, there will be no response (takes a few days for axons to die).
If some axons are degenerated, the speed of conduction can be normal but the amplitude of the response (R) is decreased independent of where the stimulation (S) is given. |
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Term
| What happens with sick myelin? |
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Definition
| Speed of conduction of compound muscle fibers is greatly slowed. Amplitude can become smaller in severe disease. |
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Term
| What happens in conduction block? |
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Definition
| There is no response (R) when the stimulation (S) is given proximal to the block. Speed and conduction are normal when it is distal, however. |
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Term
| What happens with a partial conduction block? |
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Definition
| There is decreased amplitude in response to stimulation given proximally. Normal distally. |
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