NCS FINAL EXAM QUESTIONS ANSWERED CORRECTLY LATEST UPDATE 2026
Electrical problems in NCS - Answers Usually caused by impedance, poor electrode contact, or
grounding issues
Resistance - Answers Opposition to current flow (measured in ohms)
Impedance - Answers Total opposition to current in tissue including skin, electrodes, and tissue
properties
High impedance effects - Answers Noisy baseline, low amplitude, inconsistent responses
Why sensory studies are affected first - Answers SNAPs are small and not amplified by muscle
Ohm's Law - Answers V = I × R
If resistance increases - Answers Current or voltage must increase
How to reduce impedance - Answers Clean skin, remove oils, use gel, secure electrodes
Ground electrode function - Answers Reduces noise and provides patient safety
Ground placement - Answers Between stimulator and recording electrodes
Why only one ground - Answers Prevents ground loops and noise
Signs of poor grounding - Answers 60 Hz noise, unstable baseline, distorted waveforms
Central line risk - Answers Direct pathway to heart increases electrical danger
Equipment safety rule - Answers Never turn equipment on/off while electrodes are attached
Pacemaker precaution - Answers Avoid stimulation near device
Purpose of filters - Answers Remove unwanted electrical noise
Motor filter settings - Answers LFF 2 Hz, HFF 10 kHz
Sensory filter settings - Answers LFF 20 Hz, HFF 3 kHz
Sweep speed - Answers Controls time (ms/div)
Sensitivity (gain) - Answers Controls amplitude (mV or µV)
Latency - Answers Time from stimulus to first deflection
What latency reflects - Answers Myelin integrity
Causes of prolonged latency - Answers Demyelination, cold limb, incorrect distance
Amplitude - Answers Height of waveform
What amplitude reflects - Answers Number of functioning axons
Low amplitude suggests - Answers Axonal loss or technical error
Conduction velocity (CV) - Answers Speed of nerve impulse
What CV reflects - Answers Myelin integrity
Slowed CV suggests - Answers Demyelination
Duration - Answers Time from onset to return to baseline
Increased duration indicates - Answers Temporal dispersion
Normal amplitude + slow CV - Answers Demyelination
Low amplitude + normal CV - Answers Axonal loss
Prolonged latency + focal slowing - Answers Entrapment
Effect of cold limb - Answers Increased latency, decreased CV, increased amplitude
Normal arm temperature - Answers 30.5-33°C
Why distance measurement matters - Answers Small errors cause large CV errors
CMAP - Answers Compound muscle action potential
CMAP reflects - Answers Motor nerve, NMJ, and muscle function
Supramaximal stimulation - Answers Stimulating all nerve fibers
Why increase 20% above max - Answers Ensure full activation
SNAP - Answers Sensory nerve action potential
Why SNAPs are sensitive - Answers No muscle amplification
Sensory electrode spacing - Answers 3-4 cm between G1 and G2
Why SNAPs change early - Answers Sensory fibers are more vulnerable and not amplified
Absent SNAP + normal CMAP - Answers Sensory neuropathy
Antidromic recording advantage - Answers Larger amplitude
Antidromic disadvantage - Answers Volume conduction
Why communication matters - Answers Affects anxiety, cooperation, and data accuracy
Informed consent - Answers Understanding plus permission
When consent is required - Answers Before test, before EMG, when plan changes
Why cooperation matters - Answers Improves accuracy and reduces artifact
Signs of poor cooperation - Answers Tension, movement, holding breath
Electrical problems in NCS - Answers Usually caused by impedance, poor electrode contact, or
grounding issues
Resistance - Answers Opposition to current flow (measured in ohms)
Impedance - Answers Total opposition to current in tissue including skin, electrodes, and tissue
properties
High impedance effects - Answers Noisy baseline, low amplitude, inconsistent responses
Why sensory studies are affected first - Answers SNAPs are small and not amplified by muscle
Ohm's Law - Answers V = I × R
If resistance increases - Answers Current or voltage must increase
How to reduce impedance - Answers Clean skin, remove oils, use gel, secure electrodes
Ground electrode function - Answers Reduces noise and provides patient safety
Ground placement - Answers Between stimulator and recording electrodes
Why only one ground - Answers Prevents ground loops and noise
Signs of poor grounding - Answers 60 Hz noise, unstable baseline, distorted waveforms
Central line risk - Answers Direct pathway to heart increases electrical danger
Equipment safety rule - Answers Never turn equipment on/off while electrodes are attached
Pacemaker precaution - Answers Avoid stimulation near device
Purpose of filters - Answers Remove unwanted electrical noise
Motor filter settings - Answers LFF 2 Hz, HFF 10 kHz
Sensory filter settings - Answers LFF 20 Hz, HFF 3 kHz
Sweep speed - Answers Controls time (ms/div)
Sensitivity (gain) - Answers Controls amplitude (mV or µV)
Latency - Answers Time from stimulus to first deflection
What latency reflects - Answers Myelin integrity
Causes of prolonged latency - Answers Demyelination, cold limb, incorrect distance
Amplitude - Answers Height of waveform
What amplitude reflects - Answers Number of functioning axons
Low amplitude suggests - Answers Axonal loss or technical error
Conduction velocity (CV) - Answers Speed of nerve impulse
What CV reflects - Answers Myelin integrity
Slowed CV suggests - Answers Demyelination
Duration - Answers Time from onset to return to baseline
Increased duration indicates - Answers Temporal dispersion
Normal amplitude + slow CV - Answers Demyelination
Low amplitude + normal CV - Answers Axonal loss
Prolonged latency + focal slowing - Answers Entrapment
Effect of cold limb - Answers Increased latency, decreased CV, increased amplitude
Normal arm temperature - Answers 30.5-33°C
Why distance measurement matters - Answers Small errors cause large CV errors
CMAP - Answers Compound muscle action potential
CMAP reflects - Answers Motor nerve, NMJ, and muscle function
Supramaximal stimulation - Answers Stimulating all nerve fibers
Why increase 20% above max - Answers Ensure full activation
SNAP - Answers Sensory nerve action potential
Why SNAPs are sensitive - Answers No muscle amplification
Sensory electrode spacing - Answers 3-4 cm between G1 and G2
Why SNAPs change early - Answers Sensory fibers are more vulnerable and not amplified
Absent SNAP + normal CMAP - Answers Sensory neuropathy
Antidromic recording advantage - Answers Larger amplitude
Antidromic disadvantage - Answers Volume conduction
Why communication matters - Answers Affects anxiety, cooperation, and data accuracy
Informed consent - Answers Understanding plus permission
When consent is required - Answers Before test, before EMG, when plan changes
Why cooperation matters - Answers Improves accuracy and reduces artifact
Signs of poor cooperation - Answers Tension, movement, holding breath
