DPT 712: CLINICAL ELECTROPHYSIOLOGY EXAM
QUESTIONS WITH VERIFIED ANSWERS GRADED A++
What is EMG?
Measurement of a muscle contraction's electrical activity
The summation of action potentials from contracting muscle fibers
How do the number of muscle fibers firing relate to what is seen in the EMG?
The more muscle fibers that fire, the greater the number of APs recorded and the
greater the EMG voltage
What is intramuscular EMG?
Analyzes individual APs from a motor unit to determine the extent of nerve or muscle
damage
What is the electrical source in EMG?
The muscle membrane potential of about -90 mV. Measured EMG potentials range
between less than 50 uV and up to 20-30 mV depending on the muscle under
observation
Why is EMG needed?
Because it is the Gold Standard test for nerve function (phyisological)
Provides a better assessment of nerve damage than current diagnostic imaging
measures
,Used in conjuction with imaging studies (anatomical)
One of many diagnostic tools used for neuromuscular disorders
What are symptoms of nerve damage?
Numbness and tingling
"Funny sensation"
Weakness, fatigue, clumsiness
Pain
What are nerve damage signs?
Loss of/changes in reflexes
Falls, gait changes
Dropping items
What are locations that a nerve can be damaged?
Anterior Horn Cell (AHC)
Axon: Spinal/peripheral N
MEP/neuromuscular junction
Muscle fibers
What is the time to recovery with remyelination in neuropraxia?
2-12 weeks
What is the time to recovery in collateral sprouting and axonal regeneration in
incomplete injuries (axonotmesis) or neuropraxia?
2-6 months
What is the time to recovery for axonal regeneration in axonotmesis 2nd, 3rd, and
4th degree?
, 2-18 months
What is the time to recovery for Neurotmesis 5th degree?
No regeneration without surgical repair
What should be done in the first 0-7 days after nerve injury?
Baseline clinical examination for future comparison, no EMG since need 2 weeks for the
injury to stabilize
What should be done 10-21 days after a nerve injury?
Initial study: Axonal degeneration occurs in this time frame, so this will distinguish
axonal loss from demyelination. Assesses extent of axonal loss (reduced CMAP
amplitude on NCV and number of MUPs with max contraction
What should be done 3 to 6 months after a nerve injury?
Follow-up study: Documents extent of reinnervation in distant muscles
What should be done 2 years after a nerve injury?
This is the maximum time for functional reinnervation
What can diagnostic EMG be used to study?
Motor unit's intrinsic electrical activity
Based on innervation of muscle fiber by LMN (alpha motor neuron)
Clinically useful in studying: Anterior Horn Cell, nerve root, peripheral nerve, muscle
Under what four conditions is audio and visual information obtained during EMG
instrumentation?
1. Inserting/moving needle
2. At rest
QUESTIONS WITH VERIFIED ANSWERS GRADED A++
What is EMG?
Measurement of a muscle contraction's electrical activity
The summation of action potentials from contracting muscle fibers
How do the number of muscle fibers firing relate to what is seen in the EMG?
The more muscle fibers that fire, the greater the number of APs recorded and the
greater the EMG voltage
What is intramuscular EMG?
Analyzes individual APs from a motor unit to determine the extent of nerve or muscle
damage
What is the electrical source in EMG?
The muscle membrane potential of about -90 mV. Measured EMG potentials range
between less than 50 uV and up to 20-30 mV depending on the muscle under
observation
Why is EMG needed?
Because it is the Gold Standard test for nerve function (phyisological)
Provides a better assessment of nerve damage than current diagnostic imaging
measures
,Used in conjuction with imaging studies (anatomical)
One of many diagnostic tools used for neuromuscular disorders
What are symptoms of nerve damage?
Numbness and tingling
"Funny sensation"
Weakness, fatigue, clumsiness
Pain
What are nerve damage signs?
Loss of/changes in reflexes
Falls, gait changes
Dropping items
What are locations that a nerve can be damaged?
Anterior Horn Cell (AHC)
Axon: Spinal/peripheral N
MEP/neuromuscular junction
Muscle fibers
What is the time to recovery with remyelination in neuropraxia?
2-12 weeks
What is the time to recovery in collateral sprouting and axonal regeneration in
incomplete injuries (axonotmesis) or neuropraxia?
2-6 months
What is the time to recovery for axonal regeneration in axonotmesis 2nd, 3rd, and
4th degree?
, 2-18 months
What is the time to recovery for Neurotmesis 5th degree?
No regeneration without surgical repair
What should be done in the first 0-7 days after nerve injury?
Baseline clinical examination for future comparison, no EMG since need 2 weeks for the
injury to stabilize
What should be done 10-21 days after a nerve injury?
Initial study: Axonal degeneration occurs in this time frame, so this will distinguish
axonal loss from demyelination. Assesses extent of axonal loss (reduced CMAP
amplitude on NCV and number of MUPs with max contraction
What should be done 3 to 6 months after a nerve injury?
Follow-up study: Documents extent of reinnervation in distant muscles
What should be done 2 years after a nerve injury?
This is the maximum time for functional reinnervation
What can diagnostic EMG be used to study?
Motor unit's intrinsic electrical activity
Based on innervation of muscle fiber by LMN (alpha motor neuron)
Clinically useful in studying: Anterior Horn Cell, nerve root, peripheral nerve, muscle
Under what four conditions is audio and visual information obtained during EMG
instrumentation?
1. Inserting/moving needle
2. At rest
