CCNT key terms

A nerve cell and its axon that originate in the cerebral cortex or brainstem and descend to synapse on lower motor neurons or interneurons in the spinal cord. Damage produces weakness, spasticity, hyperreflexia, and a Babinski sign without muscle atrophy.

A neuron whose cell body lies in the spinal cord anterior horn or a brainstem motor nucleus and whose axon innervates skeletal muscle directly. Injury causes flaccid weakness, atrophy, fasciculations, and diminished reflexes.

An abnormal plantar reflex in which stroking the lateral sole causes extension (dorsiflexion) of the great toe, often with fanning of the other toes. In adults it indicates corticospinal tract dysfunction.

The distorted map of the body represented along the precentral and postcentral gyri, where body parts with fine control or sensation occupy disproportionately large cortical areas. It helps localize lesions by predicting which body region is affected.

The strip of skin supplied by sensory fibers from a single spinal nerve root. Clinicians use dermatomal maps to localize radiculopathy and to interpret somatosensory evoked potential abnormalities.

The group of muscles innervated by motor fibers of a single spinal nerve root. Testing myotomes by resisted movement helps distinguish a root lesion from a peripheral nerve or plexus lesion.

Clear fluid produced mainly by the choroid plexus that cushions the brain and spinal cord and circulates through the ventricles and subarachnoid space. Its presence alters electrical conductivity and must be considered when interpreting recordings near the skull.

An amplifier that boosts the voltage difference between two input electrodes while rejecting voltage common to both. Its ability to suppress shared interference is the basis of common-mode rejection in EEG and evoked potential recording.

A figure expressing how strongly an amplifier rejects a signal appearing equally at both inputs relative to the differential signal it amplifies. Higher ratios mean better rejection of interference such as 60 Hz mains noise.

The opposition to current flow presented by an amplifier's input. It must be far higher than electrode impedance so that most signal voltage reaches the amplifier rather than being lost across the electrodes.

The input voltage needed to produce a specified deflection on the display, commonly expressed in microvolts per millimeter for EEG. Adjusting sensitivity changes how large waveforms appear without altering the recorded signal.

A band-stop filter that sharply attenuates a narrow frequency range, most often 50 or 60 Hz, to reduce mains interference. Overuse can distort real EEG activity and create ringing, so it should not replace good electrode technique.

The alternating-current resistance measured between an electrode and the skin or scalp. High or unbalanced impedance increases noise and artifact, so technologists check and reduce it before recording.

An unintended conductive path, often from excess electrode paste or sweat, that electrically connects two electrodes. It falsely lowers measured impedance and can make two channels record nearly identical activity.

An international method of placing scalp electrodes at measured proportional distances between landmarks such as the nasion and inion. Electrode names combine a region letter with a number, odd on the left and even on the right.

The ordered arrangement showing which electrodes are connected to each amplifier channel and how they are paired. The same EEG looks different under different montages, so technologists select montages suited to the clinical question.

A display in which each channel records the voltage difference between two adjacent scalp electrodes, such as Fp1-F3. It localizes focal activity well because a phase reversal appears at the electrode common to involved channels.

A display in which each channel compares one scalp electrode with a single common reference, such as linked ears or an average reference. It shows the true amplitude at each site but can spread activity from an active reference.

The pattern in which two adjacent bipolar channels deflect toward each other because the shared electrode has the highest voltage. Identifying the phase-reversing electrode localizes a focal discharge or lesion.

A posteriorly dominant rhythm of roughly 8 to 13 Hz seen in relaxed, awake adults with eyes closed. It attenuates with eye opening and is a key marker of normal background organization.

A normal arch-shaped rhythm near 7 to 11 Hz over the central regions, suppressed by movement or thought of movement of the contralateral limb. It can be mistaken for a focal abnormality if its reactivity is not tested.

The ongoing, nonparoxysmal EEG rhythms that reflect the brain's general state, judged by frequency, amplitude, symmetry, and reactivity. Its organization helps distinguish normal variation from diffuse encephalopathy.

A spike, sharp wave, or spike-and-wave complex that stands out from background and suggests cortical hyperexcitability. Such discharges support but do not by themselves confirm a diagnosis of epilepsy.

A maneuver such as hyperventilation, photic stimulation, sleep, or sleep deprivation used during EEG to provoke or reveal abnormal activity. Each has expected normal effects that must be recognized to avoid misinterpretation.

A averaged cortical response recorded over occipital regions after a patterned or flash visual stimulus. Prolonged latency of the P100 wave commonly reflects demyelination of the optic nerve.

A series of short-latency waves, labeled I through V, recorded from the scalp within about 10 milliseconds after a click stimulus. Interpeak latencies help assess the auditory nerve and brainstem pathways.

A response recorded over the spine and scalp after electrical stimulation of a mixed peripheral nerve such as the median nerve. It assesses large-fiber sensory pathways from limb to cortex.

A signal-processing method that sums many stimulus-locked trials and divides by their number, so random noise cancels while the consistent evoked response grows. The number of trials traded for recording time and patient comfort.

The electrical waveform produced by the muscle fibers of one motor unit firing together, recorded with a needle electrode. Its duration, amplitude, and shape help distinguish neuropathic from myopathic disease.

A spontaneous, brief, small-amplitude discharge of a single denervated muscle fiber seen on needle EMG at rest. Its presence indicates active denervation, typically appearing weeks after nerve injury.

The orderly addition of motor units as voluntary effort increases, normally beginning with smaller units and progressing to larger ones. Reduced or early recruitment patterns help localize nerve versus muscle disorders.

The speed at which an action potential travels along a nerve, calculated from the distance between stimulation sites divided by the latency difference. Slowing suggests demyelination, while amplitude loss suggests axonal loss.

A late response produced by submaximal electrical stimulation that activates Ia afferents and evokes a reflex muscle contraction. Comparing its latency with the M wave helps evaluate proximal nerve conduction and radiculopathy.

A process in which the patient voluntarily agrees to a procedure after receiving understandable information about its purpose, risks, benefits, and alternatives. It must be documented and may be withdrawn at any time.

The ethical and legal duty to protect identifiable health information from unauthorized disclosure. It applies to records, images, and conversations, and exceptions such as required reporting must be handled carefully.

Infection-control practices applied to all patients regardless of diagnosis, including hand hygiene, gloves, and protection from blood and body fluids. They are the foundation for preventing transmission during electrode placement and needle studies.

Cleaning hands with soap and water or alcohol-based rub at specified moments before and after patient contact. It is the single most effective measure for reducing healthcare-associated infection during neurodiagnostic procedures.

A low-resistance path that carries stray current safely to earth rather than through the patient. Proper grounding of equipment and avoiding lifted grounds reduce shock and burn risk during recordings.