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Electromyography
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Electromyography

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Questions and Answers

What is indicated by a short-duration, low-amplitude polyphasic potential?

  • Muscle hyperactivity
  • Normal recruitment of muscle fibers
  • Increased number of motor units
  • Decreased recruitment of muscle fibers (correct)

    • What characterizes the H reflex in terms of its wave appearance?

  • Triphasic potential (correct)
  • Monophasic potential
  • Biphasic potential
  • Tetraphasic potential

    • What happens to individual motor units in myopathy?

  • Decreased number of motor units
  • Increased number of muscle fibers per unit
  • Increased recruitment for voluntary activity (correct)
  • Decreased motor neuron activity

    • Which of the following describes the recruitment density in weak muscles due to myopathy?

    <p>Normal recruitment density</p> Signup and view all the answers

    What is the expected duration range for normal Motor Unit Action Potentials (MUAPs)?

    <p>2-15 msec</p> Signup and view all the answers

    How does a neuropathic potential differ in amplitude from myopathic potential?

    <p>Higher amplitude than normal</p> Signup and view all the answers

    What factor contributes to the short duration of the myopathic potential?

    <p>Low number of muscle fibers recruited</p> Signup and view all the answers

    In a healthy muscle response, the recruitment of motor units typically results in what type of potential?

    <p>Polyphasic, high amplitude</p> Signup and view all the answers

    What best explains the mechanism of the H reflex?

    <p>It involves both sensory and motor nerves</p> Signup and view all the answers

    Which statement is true about recruitment in myopathy compared to healthy muscles?

    <p>Myopathic muscles have normal recruitment density</p> Signup and view all the answers

    What type of electrode is used in Intramuscular Electromyography (nEMG)?

    <p>Needle electrode</p> Signup and view all the answers

    Which of the following statements about the Nerve Conduction Study (NCS) is correct?

    <p>It measures the speed and strength of signals between skin-applied electrodes.</p> Signup and view all the answers

    During an nEMG procedure, what does the neurologist instruct the patient to do?

    <p>Contract and rest the muscle</p> Signup and view all the answers

    What information can be obtained from Electromyography?

    <p>Muscle response during both rest and movement</p> Signup and view all the answers

    In terms of clinical correlation, what differentiates neuropathy from myopathy?

    <p>Neuropathy results from axonal degeneration; myopathy does not.</p> Signup and view all the answers

    Which of the following is NOT a type of Electromyography mentioned?

    <p>Ultrasound Electromyography</p> Signup and view all the answers

    What is the role of a needle electrode in Intramuscular Electromyography?

    <p>To measure electrical activity in the muscle</p> Signup and view all the answers

    What might a fracture of the upper arm bone (humerus) potentially damage?

    <p>The radial nerve</p> Signup and view all the answers

    How is the principle of Nerve Conduction Study used in clinical settings?

    <p>To evaluate nerve damage classification</p> Signup and view all the answers

    What does Intramuscular Electromyography primarily measure?

    <p>Muscle response or electrical activity</p> Signup and view all the answers

    What is a characteristic of polyphasic potentials?

    <p>They are nonspecific findings.</p> Signup and view all the answers

    What causes the increased amplitude of long-duration potentials observed in neuropathic conditions?

    <p>Increased motor unit recruitment after reinnervation.</p> Signup and view all the answers

    What happens to the action potential transmission during voluntary activity in neuropathy?

    <p>It decreases, leading to compensatory mechanisms.</p> Signup and view all the answers

    After reinnervation, what happens to surviving axons?

    <p>They branch to innervate adjacent muscle fibers.</p> Signup and view all the answers

    Which of the following best describes the recruitment of motor units in neuropathy?

    <p>There is decreased recruitment density and overall recruitment.</p> Signup and view all the answers

    What percentage of normal muscles may exhibit polyphasic potentials?

    <p>10-15%</p> Signup and view all the answers

    What is a long-duration, high-amplitude potential referred to in neuropathy?

    <p>Neuropathic potential.</p> Signup and view all the answers

    What primarily affects the difficulty in impulse transmission to muscles in neuropathy?

    <p>Rate of remaining motor units firing.</p> Signup and view all the answers

    How are muscle fibers affected after reinnervation in neuropathic issues?

    <p>They increase in number per motor unit.</p> Signup and view all the answers

    What type of muscle activity is affected due to lower action potential transmission in neuropathy?

    <p>Voluntary activity.</p> Signup and view all the answers

    What is the primary purpose of an EMG?

    <p>To detect abnormalities in neuromuscular function</p> Signup and view all the answers

    What defines the conduction velocity in an EMG report?

    <p>The time it takes for the electrical impulse to travel along the nerve</p> Signup and view all the answers

    Which type of electromyography is characterized by non-invasive electrodes?

    <p>Surface electromyography (sEMG)</p> Signup and view all the answers

    What does the amplitude in an EMG report represent?

    <p>The height of the electrical signal wave</p> Signup and view all the answers

    What is a disadvantage of surface electromyography (sEMG)?

    <p>It is less effective for deep muscle analysis</p> Signup and view all the answers

    Which of the following parameters indicates a reduction of a signal across an anatomical region?

    <p>Conduction block</p> Signup and view all the answers

    What does the F wave represent in electromyography?

    <p>An electrical echo along the motor nerve</p> Signup and view all the answers

    What is indicated if nerve function does not return within four months after injury?

    <p>Possible permanent nerve damage</p> Signup and view all the answers

    Which of the following statements about needle electromyography (nEMG) is true?

    <p>It is primarily used to examine deep muscle activity</p> Signup and view all the answers

    What best describes the scenario when electrical activity is detected during rest?

    <p>Abnormal muscle condition</p> Signup and view all the answers

    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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    Related Documents

    PHYSIOLOGY_LC4_ELECTROMYOGRAPHY.pdf

    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.

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