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Questions and Answers
What is indicated by a short-duration, low-amplitude polyphasic potential?
What is indicated by a short-duration, low-amplitude polyphasic potential?
What characterizes the H reflex in terms of its wave appearance?
What characterizes the H reflex in terms of its wave appearance?
What happens to individual motor units in myopathy?
What happens to individual motor units in myopathy?
Which of the following describes the recruitment density in weak muscles due to myopathy?
Which of the following describes the recruitment density in weak muscles due to myopathy?
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What is the expected duration range for normal Motor Unit Action Potentials (MUAPs)?
What is the expected duration range for normal Motor Unit Action Potentials (MUAPs)?
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How does a neuropathic potential differ in amplitude from myopathic potential?
How does a neuropathic potential differ in amplitude from myopathic potential?
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What factor contributes to the short duration of the myopathic potential?
What factor contributes to the short duration of the myopathic potential?
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In a healthy muscle response, the recruitment of motor units typically results in what type of potential?
In a healthy muscle response, the recruitment of motor units typically results in what type of potential?
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What best explains the mechanism of the H reflex?
What best explains the mechanism of the H reflex?
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Which statement is true about recruitment in myopathy compared to healthy muscles?
Which statement is true about recruitment in myopathy compared to healthy muscles?
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What type of electrode is used in Intramuscular Electromyography (nEMG)?
What type of electrode is used in Intramuscular Electromyography (nEMG)?
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Which of the following statements about the Nerve Conduction Study (NCS) is correct?
Which of the following statements about the Nerve Conduction Study (NCS) is correct?
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During an nEMG procedure, what does the neurologist instruct the patient to do?
During an nEMG procedure, what does the neurologist instruct the patient to do?
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What information can be obtained from Electromyography?
What information can be obtained from Electromyography?
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In terms of clinical correlation, what differentiates neuropathy from myopathy?
In terms of clinical correlation, what differentiates neuropathy from myopathy?
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Which of the following is NOT a type of Electromyography mentioned?
Which of the following is NOT a type of Electromyography mentioned?
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What is the role of a needle electrode in Intramuscular Electromyography?
What is the role of a needle electrode in Intramuscular Electromyography?
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What might a fracture of the upper arm bone (humerus) potentially damage?
What might a fracture of the upper arm bone (humerus) potentially damage?
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How is the principle of Nerve Conduction Study used in clinical settings?
How is the principle of Nerve Conduction Study used in clinical settings?
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What does Intramuscular Electromyography primarily measure?
What does Intramuscular Electromyography primarily measure?
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What is a characteristic of polyphasic potentials?
What is a characteristic of polyphasic potentials?
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What causes the increased amplitude of long-duration potentials observed in neuropathic conditions?
What causes the increased amplitude of long-duration potentials observed in neuropathic conditions?
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What happens to the action potential transmission during voluntary activity in neuropathy?
What happens to the action potential transmission during voluntary activity in neuropathy?
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After reinnervation, what happens to surviving axons?
After reinnervation, what happens to surviving axons?
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Which of the following best describes the recruitment of motor units in neuropathy?
Which of the following best describes the recruitment of motor units in neuropathy?
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What percentage of normal muscles may exhibit polyphasic potentials?
What percentage of normal muscles may exhibit polyphasic potentials?
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What is a long-duration, high-amplitude potential referred to in neuropathy?
What is a long-duration, high-amplitude potential referred to in neuropathy?
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What primarily affects the difficulty in impulse transmission to muscles in neuropathy?
What primarily affects the difficulty in impulse transmission to muscles in neuropathy?
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How are muscle fibers affected after reinnervation in neuropathic issues?
How are muscle fibers affected after reinnervation in neuropathic issues?
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What type of muscle activity is affected due to lower action potential transmission in neuropathy?
What type of muscle activity is affected due to lower action potential transmission in neuropathy?
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What is the primary purpose of an EMG?
What is the primary purpose of an EMG?
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What defines the conduction velocity in an EMG report?
What defines the conduction velocity in an EMG report?
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Which type of electromyography is characterized by non-invasive electrodes?
Which type of electromyography is characterized by non-invasive electrodes?
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What does the amplitude in an EMG report represent?
What does the amplitude in an EMG report represent?
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What is a disadvantage of surface electromyography (sEMG)?
What is a disadvantage of surface electromyography (sEMG)?
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Which of the following parameters indicates a reduction of a signal across an anatomical region?
Which of the following parameters indicates a reduction of a signal across an anatomical region?
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What does the F wave represent in electromyography?
What does the F wave represent in electromyography?
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What is indicated if nerve function does not return within four months after injury?
What is indicated if nerve function does not return within four months after injury?
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Which of the following statements about needle electromyography (nEMG) is true?
Which of the following statements about needle electromyography (nEMG) is true?
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What best describes the scenario when electrical activity is detected during rest?
What best describes the scenario when electrical activity is detected during rest?
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Study Notes
ELECTROMYOGRAPHY (EMG)
- Measures electrical activity in muscles, reflecting nerve stimulation
- Used to diagnose neuromuscular abnormalities, especially peripheral neuropathy
- Consists of three types: Surface (sEMG), Needle (nEMG), and Nerve Conduction Study (NCS)
SURFACE ELECTROMYOGRAPHY (sEMG)
- Uses surface electrodes placed on the skin
- Measures muscle activity in response to surface stimulation
- Advantages: Covers larger area compared to nEMG.
- Disadvantages: More prone to interference in readings
INTRAMUSCULAR ELECTROMYOGRAPHY (NEMG)
- Uses needle electrodes inserted directly into muscles
- Records electrical activity in the targeted muscle during rest and movement
- Electrical activity during rest is considered abnormal
- Helps identify nerve damage that may not be evident physically. For example, a fractured humerus can pinch the radial nerve
NERVE CONDUCTION STUDY (NCS)
- Measured by applying electrodes to the skin
- Measures speed and strength of signals traveling between two points
- Helps classify neuropathy as either axonal degeneration or segmental demyelination
- Often paired with nEMG to provide a comprehensive understanding of nerve function
EMG Procedure
- A needle electrode is inserted into the muscle
- The neurologist instructs the patient to contract and relax the muscle
- The needle records muscle activity during both states
EMG/NCS Report Parameters
- Amplitude: Height of the electrical signal wave
- Conduction Velocity (CV): Speed of impulse transmission along the nerve
- Duration: Width of the electrical signal wave
- Conduction Block: Reduction in signal strength across a specific region
- F Wave: An electrical echo that travels up and down the nerve, measures conduction along the entire motor nerve
- H Wave: Electrical equivalent of a leg reflex, stimulated by a sensory nerve and returned through a motor nerve
Normal Motor Unit Action Potential (MUAP)
- Typically biphasic or triphasic
- Duration of 2-15 milliseconds
- Amplitude of 200 microvolts to 3 millivolts
Polyphasic Potentials (>4 phases)
- Non-specific, can occur in both neurological and myogenic diseases
- Present in small numbers (10-15%) in all normal muscles
CLINICAL CORRELATIONS: MYOPATHY
- Decreased number of muscle fibers in individual units, but normal number of motor units
- Full recruitment in weak muscles
- Increased recruitment density due to individual motor units producing less tension
- Short-duration, low-amplitude, polyphasic potential ("myopathic potential")
- Short duration due to fewer muscle fibers reached
- Low amplitude due to decreased muscle fiber recruitment
CLINICAL CORRELATIONS: NEUROPATHY
- Decreased number of motor units and recruitment density
- Increased firing rates of remaining motor units to compensate for fewer units
- Long-duration, high-amplitude, polyphasic potential ("neuropathic potential")
- Long duration due to difficulty transmitting impulses
- High amplitude due to increased motor unit recruitment after reinnervation
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Description
Test your knowledge on Electromyography (EMG), its types, and applications. This quiz covers Surface EMG (sEMG), Intramuscular EMG (nEMG), and Nerve Conduction Study (NCS). Learn about their functions, advantages, and disadvantages in diagnosing neuromuscular conditions.
