EP Flashcards
What is the definition of evoked potential?
The average of multiple responses
What is the definition of evoked response?
The electrical recording following a single stimulus
How does visual input travel?
From the retina to the optic nerve, optic chiasm, optic Tract, lateral geniculate body, and optic radiation and finally reaches the occipital cortex.
What is the function of the CNS?
Collects information from environment & body through sensory input, compared and contrast information with past informations, then decides a motor response.
What is MUAP?
Motor unit action potential
What is the neuro muscular junction (NMJ)?
A chronicle synapse cause by motor neurons & muscle fibers.
What does the anterior horn cell do?
Transmits info through nerves to muscles this is the NMJ process
What kind of fibers are measured in NCS?
Large mylinated fibers are the fibers that are measured in NCS.
Neuropothies that preferentially affect only small fibers may not reveal any abnormalities on NCS
Maybe in EMG
The largest & fasted fibers in the peripheral nervous system are not recorded during routine motor or sensory NCS.
These are the muscle afferent, very nosey Like when we test the signal and ask the patient to push against thumb.
What is volume conduction?
The process of initial intracellular electrical potential being trans omitted through extracellular fluid & tissue.
Which is essential the process of NMJ (neuro muscular junction)
What is a near field potential?
When you are recording close to the source.
What is a far-field action potential?
Electrical potentials that are distributed widely & instantly.
Far-field potentials are more often concerned in EP’s but occasional important in NCS’s
What is the morphology produced by a near-field potential?
Near-field potentials produce a triphasic waveform as an advancing action potential approached & then passes beneath and away from a recording electrode.
What is the definition of “end plate”?
End plate is when the active electrode (recording electrode) is directly over the motor point of the muscle.
What will the morphology of the wave look like if the cathode is off the motor point?
A classic triphasic wave.
Depolarization begins distally and then travels under and past the active electrode resulting in initial positive deflection.
What will the morphology of the wave look like if the cathode is placed on the end plate?
Initial negative wave followed by subsequent positive wave.
Depolarization occurs first at site, with depolarization subsequently spreading away.
What will the morphology of the wave look like of the cathode is place at a distance from the motor point?
Only a small positive wave will be seen
Definition of “cathode”
The stimulator
Definition of “CMAP”
Compound muscle action potential.
A summation of all underlying individual muscle fiber action potentials
(latency, amplitude, duration)
How are far-field potentials recorded?
Far-field potentials are recorded with two recording electrodes, one closer & the other farther from the source, they essentially see the source at the same time.
What range are motor response studies typically within?
Millivolts (mV) range
What range are sensory and mixed electrodes typically within?
Microvolts (uV) range
What is the Belly-tendon montage?
When G1 is placed over the end plate and G2 is placed distally, over the tendon of the muscle.
In CMAP what does latency represent?
Latency represents 3 separate process:
- the nerve conduction time from the stim to the NMJ.
- the delay across the NMJ.
- depolarization time across the muscle.
In CMAP what is the amplitude and how is it measured?
Amplitude is measured from baseline to the negative peak.
What is usually The reason for a CMAP low amplitude wave
Low amplitude is often the result of (axonal loss, demyelination & some NMJ disorders & neuropathies
In CMAP what is the area?
The area above the baseline to negative peak
In CMAP what is duration?
The duration is a measure from the initial deflections from baseline to the first baseline crossing.
How is motor conduction velocity calculated?
Motor conduction velocity is calculated by dividing the distance traveled by the nerve conduction time.
To calculate a true motor conduction velocity, without including NMJ transmission & muscle depolarization times, two stimulation sites must be used, one distal and one proximal.
Conduction velocity formula:
Distance between proximal and distal stim site \ proximal latency - distal latency
