CNIM key terms

The steady voltage difference across a neuron's membrane at rest, roughly −70 mV inside relative to outside, maintained mainly by potassium leak channels and the sodium-potassium pump.

A rapid, all-or-none reversal of membrane voltage that travels along an axon once depolarization reaches threshold, carrying information from one part of a neuron to another.

The synapse where a motor nerve terminal releases acetylcholine onto nicotinic receptors of a muscle fiber, producing an endplate potential that can trigger contraction.

A neuron whose cell body sits in motor cortex or brainstem and whose axon descends in the corticospinal or corticobulbar tract to influence lower motor neurons.

A neuron with its cell body in the spinal anterior horn or a cranial nerve nucleus whose axon directly innervates skeletal muscle; injury produces weakness, atrophy, and fasciculations.

The strip of skin supplied by sensory fibers from a single spinal nerve root, used to select stimulation and recording sites and to interpret root-level changes.

The group of muscles innervated by one spinal nerve root; myotomal mapping determines which muscles to record when monitoring motor pathways at a given surgical level.

The ascending system carrying fine touch, vibration, and joint position sense through the dorsal columns and medial lemniscus to somatosensory cortex; it generates the signals recorded in SSEPs.

The descending motor pathway running from cortical motor neurons through the internal capsule, brainstem, and pyramidal decussation to the spinal cord; it is the target of motor evoked potential monitoring.

An amplifier that magnifies the voltage difference between two active inputs while rejecting voltage common to both, improving the recorded neural signal relative to background noise.

A measure of how effectively a differential amplifier cancels signals present equally at both inputs; higher values mean better suppression of interference such as 60 Hz line noise.

A response recorded far from its generator after spread by volume conduction; it is typically low in amplitude and broad in shape, as with subcortical and scalp SSEP components.

The opposition to alternating current at the electrode-skin interface, expressed in ohms; high or unequal impedance increases noise and artifact in evoked potential recordings.

Low- and high-frequency limits that determine which frequencies a recording channel passes; overly narrow settings reduce noise but can distort or erase genuine evoked potential components.

The alveolar concentration of an inhaled anesthetic at which half of patients do not move to a standard surgical stimulus; it indexes potency and predicts dose-dependent suppression of evoked potentials.

Anesthesia maintained with intravenous agents such as propofol and opioids instead of inhaled gases; it is preferred for motor evoked potential monitoring because cortical responses are suppressed less.

Four supramaximal stimuli delivered to a motor nerve at 2 Hz to quantify neuromuscular blockade; even partial blockade can markedly reduce motor evoked potential amplitude.

A gradual decline in evoked potential amplitude over hours of otherwise stable anesthesia from cumulative drug effects and other factors; it must be told apart from a new surgical injury.

The capacity of cerebral arterioles to adjust caliber and hold cerebral blood flow nearly constant across a range of mean arterial pressures; when impaired, hypotension raises ischemic risk.

An inhaled anesthetic and analgesic that suppresses cortical motor evoked potentials and, when combined with volatile agents, can substantially reduce monitoring signals.

An NMDA-receptor antagonist used for analgesia and sedation that tends to preserve or increase motor and somatosensory evoked potential amplitudes, making it useful during total intravenous anesthesia.

Averaged cortical and subcortical responses to electrical stimulation of a peripheral nerve, used to monitor the dorsal column–medial lemniscus pathway during surgery.

Delivery of brief high-voltage pulses through scalp electrodes to excite motor cortex and elicit motor evoked potentials, usually recorded from limb muscles.

A direct descending volley recorded from the spinal cord after transcranial stimulation; it reflects corticospinal tract integrity and is relatively resistant to anesthetic suppression.

A series of short-latency waves generated by the auditory nerve and brainstem pathways within about 10 milliseconds of a click stimulus, used to monitor the eighth nerve and brainstem.

Continuous recording of muscle electrical activity without deliberate stimulation; bursts or trains suggest mechanical or thermal nerve irritation and warn of impending injury.

Electrical stimulation of tissue or hardware, such as a pedicle screw, while recording muscle responses to determine whether neural structures lie close to the stimulating probe.

Recording of summed cortical postsynaptic activity from scalp electrodes, used intraoperatively to assess cortical function, depth of anesthesia, and developing cerebral ischemia.

A shift in polarity of a recorded potential between adjacent electrodes overlying a generator, used during cortical mapping to identify the sensorimotor region.

The waveform produced by near-simultaneous discharge of the muscle fibers belonging to one motor unit, as recorded with a needle or surface electrode.

A standardized scheme for placing scalp electrodes at measured fractions between skull landmarks, making recording sites reproducible and comparable across patients and sessions.

A soft device inserted between the teeth during transcranial electrical stimulation to protect the tongue and teeth from injury caused by forceful masseter contraction.

Electrical noise picked up from power lines and nearby equipment; it appears as a regular sine wave and is reduced by low impedance, twisted leads, and proper grounding.

The reference evoked potential or EMG data collected after anesthesia and positioning but before the surgical step at risk, against which later changes are judged.

A predefined amount of change, such as a 50 percent amplitude drop in somatosensory evoked potentials, that triggers notification of the surgeon so corrective action can be taken.

The written and electronic documentation of baseline and serial recordings, stimulation parameters, anesthetic events, alerts raised, and actions taken during a monitored case.

A communication style in which the sender states a message, the receiver repeats it back, and the sender confirms, reducing misunderstanding during urgent intraoperative alerts.

The boundaries of what a monitoring technologist or professional may independently do, including who interprets data and who communicates findings to the surgical team.