EMG Basics Flashcards
(22 cards)
Where is the cell body for efferent?
alpha motor horn in spinal cord
What is a motor unit?
alpha motor neuron, axon, NMJ, all muscle fibers innervated
What type of injury is a radiculopathy?
pre-ganglionic
Where is the cell body for afferent nerves?
dorsal root ganglion
How does an EMG cathode propagate an action potential?
cathode terminal generates a negative impulse that attracts positive charges from the axon.
What is orthodromic?
Stimulating in direction of normal flow of action potential (motor testing)
What is antidromic?
Stimulating in opposite direction of normal flow of action potential (sensory testing)
What is an F wave?
long latency muscle action potential seen after supramaximal stimulation to a nerve
What is a CMAP?
summated action potentials of all the fibers of a muscle
What nerve are you testing when electrodes are placed over the APB?
median nerve
How do you measure onset latency of CMAP?
Measure from start of stimulus to start of deflection off baseline
How do you measure amplitude of CMAP?
Measure from initial deflection off baseline to peak
How do you measure duration of a CMAP?
Measure from initial deflection from baseline to return to baseline
What is a SNAP?
Sum of sensory nerve fiber AP elicited by stimulation of nerve or dorsal root
What is the standard for testing nerve conduction?
supramaximal stimulation
How is SNAP and CMAP generated?
Subtracting reference electrode from active electrode recording
What is the gain?
Amplification of the signal on the screen
What is the sweep speed?
Recording duration of the signal on the screen represented on the X-axis
Why would you change the sweep speed?
When looking for temporal dispersion in a demyelinating process
How is an F-wave elicited?
F-wave is elicited when the stimulus travels antidromically along the motor fibers and reaches the anterior horn cell at a critical time to depolarize it. The response is then fired down along the axon and causes a minimal contraction of the muscle
What is an H-reflex?
H-reflex is the electrical equivalent of the monosynaptic stretch reflex and is normally obtained in only a few muscles.
How is an H-reflex elicited?
selectively stimulating the Ia fibers of the posterior tibial or median nerve. Such stimulation can be accomplished by using slow (less than 1 pulse/second), long-duration (0.5-1 ms) stimuli with gradually increasing stimulation strength.
