R.NCS.T key terms

The summed electrical response recorded from a muscle after its nerve is stimulated. Its amplitude and latency reflect how well motor axons conduct and how many fibers respond.

The summed response recorded from a sensory nerve or its distal branches after electrical stimulation. Amplitude reflects the number of functioning sensory axons, and latency reflects conduction speed.

The time from the stimulus artifact to the onset of the CMAP. It includes conduction along the nerve plus the delay at the neuromuscular junction and muscle membrane.

The speed at which an action potential travels along a nerve, calculated by dividing the distance between two stimulation sites by the difference in their latencies. It is expressed in meters per second.

A nerve conduction technique in which the impulse travels opposite to the normal physiologic direction, with recording electrodes placed distally and stimulation proximal. Commonly used for sensory studies because responses are larger.

A nerve conduction technique in which the impulse travels in the normal physiologic direction, with stimulation distal and recording proximal. It is the standard orientation for motor studies.

A stimulus intensity high enough that all axons in the nerve are depolarized, producing the largest possible response. Increasing intensity further does not increase amplitude, confirming the response is maximal.

Loss of waveform sharpness and amplitude as faster and slower axons in a nerve conduct at different speeds. It is seen over long nerve segments or in demyelinating disease.

A late motor response produced by backfiring of antidromically activated motor neurons. It assesses proximal nerve segments and is measured by its minimal latency and persistence.

A monosynaptic reflex response recorded from muscle after submaximal nerve stimulation. It travels through the sensory and motor pathways of the spinal cord and is useful for evaluating proximal sensory and motor conduction.

An averaged electrical response recorded over the scalp or spine after stimulation of a sensory nerve. It reflects conduction along large-fiber sensory pathways from the periphery to the cortex.

A signal-processing technique that sums many repeated responses and divides by the number of trials. It improves the signal-to-noise ratio so small evoked potentials can be seen above background noise.

The relationship between the size of the true evoked potential and the background electrical noise. A higher ratio makes waveform peaks easier to identify and measure reliably.

The evoked potential recorded over the sensory cortex after peripheral stimulation. Its latency reflects the full pathway, including peripheral nerve, spinal cord, and central conduction.

The time an impulse takes to travel through the central nervous system, calculated by subtracting the peripheral segment time from the total evoked potential latency. It is used to detect central slowing.

A technique that uses a rapidly changing magnetic field to induce electrical currents in the brain and activate cortical neurons. It is used to study motor pathways and the motor cortex.

The muscle response recorded after stimulation of the motor cortex or motor pathway. Its amplitude and latency reflect the integrity of the corticospinal tract and the muscle's response.

The minimum stimulus intensity needed to produce a motor evoked potential of a defined size in a resting muscle. It reflects cortical and corticospinal excitability and varies between individuals.

A brief pause in ongoing voluntary muscle activity that follows a motor cortex stimulus. It reflects inhibitory circuits in the motor system and is measured by its duration.

A fatty insulating layer formed by Schwann cells in the peripheral nervous system that wraps around axons. It speeds conduction by allowing impulses to jump between nodes.

Small gaps in the myelin sheath where the axon membrane is exposed. Ion channels cluster here, allowing the action potential to regenerate and continue along the nerve.

The rapid jumping of an action potential from one node of Ranvier to the next along a myelinated axon. This mechanism greatly increases conduction velocity compared with unmyelinated fibers.

The synapse where a motor nerve terminal releases acetylcholine onto the muscle membrane. Transmission here creates the endplate potential that triggers muscle fiber contraction.

Fast-conducting sensory and motor axons with thick myelin and large diameter. They carry proprioception and touch and are the fibers most easily tested in routine nerve conduction studies.

An electronic device that amplifies the voltage difference between two input electrodes while rejecting signals common to both. It is the basic building block of recording systems in neurodiagnostics.

A measure of how well an amplifier rejects unwanted signals present equally at both inputs, such as electrical interference. A higher ratio means cleaner recordings.

The electrical deflection produced by the stimulating pulse itself, seen at the start of a recording. It must be distinguished from the true neural or muscle response.

Any unwanted electrical signal that interferes with a recording, such as muscle activity, movement, or electrical interference. It can obscure or mimic true responses and must be minimized.

The rate at which the display traces across the screen, usually expressed in milliseconds per division. It determines the time window shown and affects how waveform latency is measured.

The process of explaining a procedure's purpose, risks, and alternatives and confirming that the patient voluntarily agrees. It respects patient autonomy and is required before most diagnostic testing.

The ethical and legal duty to protect a patient's health information from unauthorized disclosure. It applies to records, conversations, and any data shared during testing.

The range of duties and procedures a technologist is trained and legally permitted to perform. Working outside it can harm patients and may violate licensing or certification rules.

The set of practices that protect patients and staff from harmful electrical current, including proper grounding, equipment inspection, and correct electrode placement.

The careful assessment of patients with pacemakers, implanted stimulators, or other electronic devices before applying electrical stimulation or magnetic fields. Certain devices may contraindicate testing.