R.NCS.T. Exam flashcards

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

Saltatory conduction

Propagation of action potentials jumping between nodes of Ranvier on myelinated axons, greatly increasing conduction velocity compared with unmyelinated fibers of the same diameter.

CMAP onset latency

Time from stimulus artifact to the first negative deflection of the compound muscle action potential, reflecting conduction in the fastest motor fibers.

SNAP peak latency

Time from stimulus to the negative peak of the sensory nerve action potential; it reflects the summed activity of sensory fibers.

Conduction velocity formula

Velocity equals the distance between stimulation sites divided by the difference in onset latencies at those sites, expressed in meters per second.

Conduction block

A reduction of more than 50 percent in proximal versus distal CMAP amplitude without abnormal temporal dispersion, indicating focal demyelination.

F-wave

A late motor response generated by antidromic activation of motor axons and recurrent firing of anterior horn cells, assessing proximal nerve segments.

H-reflex

A monosynaptic reflex elicited by submaximal stimulation of Ia afferents, commonly recorded from the soleus, evaluating the S1 arc.

Temporal dispersion

Prolonged and desynchronized CMAP or SNAP waveform caused by unequal conduction slowing among fibers, typical of acquired demyelinating neuropathy.

Axonal loss pattern

Reduced SNAP and CMAP amplitudes with relatively preserved conduction velocities, reflecting loss of axons rather than myelin damage.

Demyelinating pattern

Marked conduction slowing, prolonged distal latencies, and conduction block with relatively preserved amplitudes, reflecting myelin pathology.

Supramaximal stimulation

Stimulus intensity set 20 to 25 percent above the level producing a maximal response, ensuring all nerve fibers are activated.

Active recording electrode

The exploring electrode (G1) placed over the muscle belly or nerve, which records the potential relative to the reference electrode.

Reference electrode

The inactive electrode (G2) placed over a tendon or electrically inactive site, completing the differential recording circuit.

Ground electrode

An electrode placed between the stimulator and recording electrodes to reduce stimulus artifact and electrical noise.

Filter settings

Frequency limits that shape the recorded waveform; motor studies typically use 2-10 Hz to 10 kHz and sensory studies 20 Hz to 2-3 kHz.

Signal averaging

Repeated stimulation with summation of responses to improve signal-to-noise ratio, commonly used for small sensory potentials.

Skin temperature effect

Cooling slows conduction velocity by about 2 m/s per degree Celsius and prolongs latencies; limbs should be warmed before testing.

Electrode impedance

Opposition to current flow at the electrode-skin interface; it should be kept below 5 kilo-ohms to limit noise and artifact.

Sweep speed

The time base per division on the display; sensory studies typically use 2-5 ms per division and motor studies 5-10 ms per division.

Brachial plexus roots

The brachial plexus is formed by ventral rami of C5 through T1, supplying the upper extremity.

Lumbosacral plexus roots

The lumbosacral plexus arises from ventral rami of L4 through S3, supplying the lower extremity and pelvic region.

Median nerve origin

Formed by contributions from the medial and lateral cords of the brachial plexus, containing fibers from C6 through T1.

Ulnar nerve origin

Arises from the medial cord of the brachial plexus, containing fibers from C8 and T1, and passes through the cubital tunnel.

Radial nerve origin

Arises from the posterior cord of the brachial plexus, containing fibers from C5 through T1, and spirals around the humerus.

Common peroneal nerve

Branch of the sciatic nerve that wraps around the fibular head, making it vulnerable to compression and causing foot drop.

Wallerian degeneration

Degeneration of the axon distal to an injury site, followed by remyelination and regeneration at roughly 1 to 2 mm per day.

A-delta and C fibers

Small myelinated and unmyelinated fibers that transmit pain and temperature; they are tested by quantitative sensory or autonomic methods.

Informed consent

The process of explaining the purpose, risks, and alternatives of a procedure and obtaining the patient's voluntary agreement before testing.

Pacemaker precaution

Implanted cardiac devices are a relative contraindication for transthoracic stimulation; consult cardiology and avoid current paths across the chest.

Anticoagulation and EMG

Needle EMG carries increased bleeding risk in anticoagulated or thrombocytopenic patients; weigh benefit against risk and use superficial muscles.

Universal precautions

Infection control practices requiring gloves for needle procedures, sharps disposal in biohazard containers, and hand hygiene before and after patient contact.

HIPAA privacy

Federal rule requiring protection of identifiable patient health information from unauthorized disclosure in clinical and educational settings.