R.NCS.T flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Supramaximal stimulation

Stimulus intensity increased until the recorded response plateaus, ensuring all axons in the nerve are activated so amplitude and latency reflect the full nerve.

Conduction velocity formula

Velocity in meters per second equals the distance in millimeters between two stimulation sites divided by the difference in latency in milliseconds between those sites.

Temporal dispersion

With proximal stimulation, axons conduct at different speeds, so their action potentials arrive at the muscle at different times, widening and lowering the compound muscle action potential.

F-wave

A late motor response produced by antidromic activation of anterior horn cells and their backfiring, reflecting conduction along the entire proximal motor nerve segment.

H-reflex

A monosynaptic reflex recorded from the soleus after submaximal tibial nerve stimulation, reflecting sensory afferent and motor efferent conduction through the S1 root.

Axonal loss pattern

Reduced compound muscle and sensory nerve action potential amplitudes with relatively preserved conduction velocities, reflecting loss of excitable axons rather than myelin damage.

Demyelination pattern

Slowed conduction velocity, prolonged distal latency, conduction block, and temporal dispersion with relatively preserved amplitude distal to the lesion.

Temperature correction

Nerve conduction velocity falls roughly two meters per second for each degree Celsius below 34 degrees, and distal latencies prolong, so limbs must be warmed before testing.

Median SEP N20

The cortical somatosensory evoked potential recorded over the contralateral parietal scalp after median nerve stimulation, with a typical latency near 18 to 20 milliseconds.

Posterior tibial SEP P37

The cortical response recorded over the scalp after ankle stimulation of the tibial nerve, with a typical latency near 35 to 40 milliseconds, assessing lumbosacral pathways.

SEP warning criterion

During monitoring, a cortical amplitude reduction greater than 50 percent or a latency increase greater than 10 percent warrants warning the surgical team of possible neural compromise.

SEP pathway

Somatosensory evoked potentials assess the large-fiber dorsal column and medial lemniscus pathway carrying touch and proprioception, not the spinothalamic pain and temperature fibers.

Resting motor threshold

The minimum transcranial magnetic stimulator intensity that elicits motor evoked potentials of at least 50 microvolts in about half of consecutive trials in a relaxed muscle.

Central motor conduction time

Cortical latency minus the peripheral or spinal latency, isolating conduction through the intracranial and spinal corticospinal segments from the peripheral nerve segment.

MEP warning criterion

During spine surgery, a transcranial electrical motor evoked potential amplitude reduction greater than 50 to 80 percent from baseline is a warning criterion for corticospinal compromise.

TMS contraindications

Implanted electronic devices such as pacemakers and cochlear implants, intracranial metal, and a history of epilepsy are contraindications because of heating, device malfunction, or seizure risk.

Nerve fiber classes

A-alpha fibers are large and myelinated for motor and proprioception, A-beta for touch, A-delta thinly myelinated for pain, and C fibers unmyelinated for slow pain and temperature.

Median nerve course

Formed from C6 through T1 roots, the median nerve passes through the carpal tunnel and supplies thenar muscles and sensation of the first three and a half digits.

Ulnar nerve course

Arises from C8 and T1, passes the cubital tunnel and Guyon canal, and supplies most intrinsic hand muscles and sensation of the fifth digit.

Peroneal nerve entrapment

The common peroneal nerve winds around the fibular neck, where compression causes foot drop with weakness of ankle dorsiflexion and eversion.

Wallerian degeneration

After axonal injury, the distal axon degenerates and conduction fails within days; regeneration proceeds at roughly one millimeter per day with an advancing Tinel sign.

Common-mode rejection

A differential amplifier subtracts its two inputs, rejecting noise common to both; balanced low electrode impedances are required for effective rejection of mains interference.

Nyquist theorem

The sampling rate must exceed twice the highest frequency component of the signal to avoid aliasing, which would distort the recorded waveform.

Filter settings

Motor studies typically use 2 hertz to 10 kilohertz, sensory studies 20 hertz to 2 to 3 kilohertz, and evoked potentials 1 to 3 kilohertz; narrow filters distort latency and amplitude.

Averaging benefit

Averaging repeated responses improves the signal-to-noise ratio by roughly the square root of the number of trials, while artifact rejection prevents contaminated trials from corrupting the average.

Electrical stimulation safety

Avoid stimulation over the carotid sinus, anterior neck, and across the chest in patients with cardiac devices, because of reflex bradycardia and device interference risks.

Needle EMG bleeding risk

Anticoagulation, thrombocytopenia, and coagulopathy increase hematoma risk; assess risk, avoid deep or vascular muscles, and apply prolonged pressure after needle withdrawal.

Informed consent

Disclose the purpose, risks such as discomfort, bleeding, or seizure, benefits, and alternatives of the procedure, and document the discussion in the record.

Documentation integrity

Record raw waveforms, technical parameters, and limitations accurately; never fabricate, alter, or selectively report data, and refer ambiguous findings for physician interpretation.

Carpal tunnel syndrome NCS

Prolonged median distal sensory and motor latencies, reduced median sensory amplitude, and sometimes thenar denervation, with normal ulnar studies, indicate median neuropathy at the wrist.

Guillain-Barré syndrome NCS

Early demyelinating features include prolonged distal latencies, slowed conduction, conduction block, and prolonged F-waves, with amplitudes relatively preserved early in the course.

Diabetic polyneuropathy NCS

Length-dependent axonal loss produces reduced sensory and motor amplitudes with mild slowing, affecting the lower limbs first in a stocking distribution.