Electromyography Course Outline

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Questions and Answers

What is a characteristic of polyphasic potentials in electromyography?

Are always indicative of muscle damage

Can be found in small percentages in normal muscles (correct)

Are specific to myogenic diseases

Only occur in neurogenic diseases

What is a consequence of decreased number of motor units in neuropathy?

Enhanced firing rate of all motor units

Increased conduction velocity of impulses

Reduced recruitment density and overall recruitment (correct)

Increased overall action potential transmission

What occurs after the process of reinnervation in motor units?

The number of muscle fibers per unit decreases

Surviving axons branch to innervate more muscle fibers (correct)

Surviving axons degenerate further

Adjacent muscle fibers are no longer innervated

What is the primary purpose of intramuscular electromyography (nEMG)?

To measure the electrical activity in a specific muscle Signup and view all the answers

What leads to the high amplitude observed in neuropathic potentials?

Increased motor unit recruitment after reinnervation Signup and view all the answers

What is the primary cause of long-duration potentials in neuropathic EMG?

Difficulty in impulse transmission to muscle or motor unit Signup and view all the answers

Which type of electromyography involves the use of electrode stickers applied to the skin?

Surface electromyography (sEMG) Signup and view all the answers

Which of the following is a nonspecific finding in electromyography?

Polyphasic potentials with more than four phases Signup and view all the answers

In the context of electromyography, what does the procedure typically involve?

Assessing muscle electrical activity during both rest and movement Signup and view all the answers

What happens to the firing rate of surviving motor units during voluntary activity in neuropathy?

Increases at which remaining units begin firing Signup and view all the answers

What are the two types of dysfunctions compared in the clinical correlation of electromyography?

Neuropathy vs. myopathy Signup and view all the answers

What does a nerve conduction study (NCS) primarily measure?

The speed and strength of signals traveling between points Signup and view all the answers

Which of the following best describes the relationship between amplitude and excitation in motor units post-reinnervation?

Increased excitation results in increased amplitude Signup and view all the answers

During intramuscular electromyography, when is the needle electrode typically recording muscle activity?

Throughout both rest and voluntary movement phases Signup and view all the answers

What do surface electrodes in a nerve conduction study help classify?

Neuropathy as due to axonal degeneration or demyelination Signup and view all the answers

What is one of the implications of a fracture in the upper arm bone related to nerve function?

It may lead to nerve pinch or tear, affecting muscle function Signup and view all the answers

What does the electrical activity detected during rest in an EMG indicate?

Abnormal electrical activity Signup and view all the answers

Which parameter in an EMG report describes the height of the electrical signal waveform?

Amplitude Signup and view all the answers

What is the primary advantage of surface electromyography (sEMG) over needle electromyography (nEMG)?

Greater coverage Signup and view all the answers

What does a conduction block in an EMG report signify?

Reduction of the electrical signal Signup and view all the answers

What is the purpose of the F wave in an electromyography study?

Assesses conduction along a motor nerve Signup and view all the answers

What type of electrode configuration is typically used in surface electromyography (sEMG)?

Non-invasive surface electrodes Signup and view all the answers

In the context of nerve conduction studies, what does conduction velocity (CV) measure?

Speed of the electrical impulse Signup and view all the answers

What should be done if nerve function does not return after 4 months of injury, according to EMG practices?

Conduct an EMG to identify damage Signup and view all the answers

What characterizes the H reflex in terms of its wave type?

It is a triphasic potential. Signup and view all the answers

In myopathy, how does the recruitment of motor units typically occur?

Full recruitment occurs despite weak muscle fibers. Signup and view all the answers

What is the expected amplitude of polyphasic potentials in myopathy?

Low amplitude due to decreased muscle fibers recruited. Signup and view all the answers

What is a primary feature of the motor unit action potential (MUAP) duration in normal conditions?

MUAP duration ranges from 2 to 15 msec. Signup and view all the answers

How is the recruitment density affected in myopathy?

Recruitment density is normal. Signup and view all the answers

What happens to the duration of polyphasic potentials in myopathic conditions?

They are short due to few muscle fibers firing quickly. Signup and view all the answers

What defines the nature of the impulse in the H reflex?

It travels to the spinal cord via a sensory nerve. Signup and view all the answers

What type of potential can indicate neuropathic conditions?

Long-duration, high-amplitude polyphasic potential. Signup and view all the answers

Study Notes

Electromyography Overview

Electromyography (EMG) measures electrical activity in muscles, reflecting muscle response to nerve stimulation.
Neurophysiological technique assesses skeletal muscle activity to identify neuromuscular disorders.

Types of Electromyography

Surface Electromyography (sEMG):
- Non-invasive, uses adhesive electrodes on the skin.
- Provides time/intensity data of superficial muscle activation; advantages include broader coverage but is more prone to artifacts.
Intramuscular Electromyography (nEMG):
- Invasive method where a needle electrode is inserted directly into the muscle to record electrical activity.
Nerve Conduction Study (NCS):
- Evaluates signal speed and strength between nerve points, crucial in diagnosing neuropathies related to axonal degeneration or demyelination.

Procedures

Needle electrode is inserted into the muscle under neurologist guidance for contraction and rest testing.
Captures muscle activity in both resting and active states.

EMG/NCS Parameters

Amplitude: Height of electrical wave signal.
Conduction Velocity (CV): Speed at which electrical impulses travel along nerves.
Duration: Width of an electrical wave.
Conduction Block: Reduction of signal across anatomical regions.
F Wave: Electrical echo indicating conduction along a motor nerve.
H Reflex: Represents sensory nerve impulse travel to the spinal cord and back through motor nerves.

Clinical Correlations

Myopathy:
- Characterized by fewer muscle fibers per motor unit but normal overall motor unit count.
- Features include full recruitment of weaker muscles and short-duration, low-amplitude polyphasic potentials due to limited muscle fiber activation.
Neuropathy:
- Reveals decreased motor unit count and recruitment; low action potential transmission leads to compensatory increased firing rates of remaining units.
- Results in long-duration, high-amplitude polyphasic potentials reflecting difficulties in impulse transmission and increased fiber recruitment after reinnervation.

Key Points

EMG is vital for detecting and evaluating neuromuscular abnormalities.
Understanding EMG parameters aids in diagnosing conditions affecting muscle and nerve function.
Distinguishing between myopathy and neuropathy is crucial for correct treatment strategies.

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Description

This quiz covers the basics of electromyography (EMG) focusing on the use of invasive needle electrodes. It explores the definition, uses, and the principles behind recording electrical activity in muscles. Perfect for those studying neuromuscular physiology.