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CCNT practice questions

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Question 1Neuroanatomy and Neurophysiology

Which structure forms the myelin sheath around axons in the peripheral nervous system?

  1. Astrocyte
  2. Ependymal cell
  3. Oligodendrocyte
  4. Schwann cell Correct answer.

Explanation

In the peripheral nervous system, each Schwann cell wraps a single axon segment to form myelin, which speeds saltatory conduction. Oligodendrocytes perform the analogous role in the central nervous system, but each myelinates multiple axons.

Question 2Neuroanatomy and Neurophysiology

A lesion of the left optic nerve before the optic chiasm produces which visual field deficit?

  1. Total blindness of the left eye Correct answer.
  2. Total blindness of the right eye
  3. Bitemporal hemianopia
  4. Right homonymous hemianopia

Explanation

The optic nerve carries all fibers from the ipsilateral retina, so a prechiasmal lesion on the left abolishes vision in the left eye entirely. Chiasmal and postchiasmal lesions produce the hemianopias because they interrupt crossing or post-crossing fibers.

Question 3Neuroanatomy and Neurophysiology

Which cranial nerve carries parasympathetic fibers that slow the heart rate?

  1. Glossopharyngeal nerve (CN IX)
  2. Trigeminal nerve (CN V)
  3. Facial nerve (CN VII)
  4. Vagus nerve (CN X) Correct answer.

Explanation

The vagus nerve supplies parasympathetic fibers to the sinoatrial and atrioventricular nodes via the cardiac branches, reducing heart rate. The glossopharyngeal and facial nerves carry parasympathetic fibers to salivary and lacrimal glands, not the heart.

Question 4Neuroanatomy and Neurophysiology

Destruction of the left corticospinal tract in the internal capsule most likely produces which finding?

  1. Right-sided spastic weakness with hyperreflexia Correct answer.
  2. Right-sided loss of pain and temperature sensation
  3. Left-sided flaccid weakness with areflexia
  4. Bilateral lower-extremity weakness

Explanation

Corticospinal fibers decussate in the medulla, so a left internal capsule lesion causes contralateral (right) upper motor neuron signs: spasticity, hyperreflexia, and a Babinski sign. Lower motor neuron lesions instead cause flaccid weakness with areflexia.

Question 5Neuroanatomy and Neurophysiology

Which cerebellar region is most associated with midline truncal ataxia and gait instability?

  1. Vermis Correct answer.
  2. Dentate nucleus
  3. Cerebellar hemisphere
  4. Flocculonodular lobe

Explanation

The vermis controls axial and proximal musculature, so its damage causes wide-based gait and truncal instability. The hemispheres coordinate distal limb movements, and the flocculonodular lobe governs eye movements and balance.

Question 6Neuroanatomy and Neurophysiology

Which neurotransmitter is released at the neuromuscular junction to trigger skeletal muscle contraction?

  1. Glutamate
  2. Acetylcholine Correct answer.
  3. GABA
  4. Dopamine

Explanation

Motor neurons release acetylcholine, which binds nicotinic receptors on the motor end plate and depolarizes the muscle fiber. Dopamine, GABA, and glutamate act centrally rather than at the skeletal neuromuscular junction.

Question 7Neuroanatomy and Neurophysiology

The primary somatosensory cortex is located in which gyrus?

  1. Cingulate gyrus
  2. Postcentral gyrus Correct answer.
  3. Precentral gyrus
  4. Superior temporal gyrus

Explanation

The postcentral gyrus of the parietal lobe houses the primary somatosensory cortex, which receives thalamocortical input for touch and proprioception. The precentral gyrus contains the primary motor cortex.

Question 8Neuroanatomy and Neurophysiology

Which tract carries conscious proprioception and fine touch from the lower limb to the brainstem?

  1. Ventral spinocerebellar tract
  2. Lateral spinothalamic tract
  3. Rubrospinal tract
  4. Fasciculus gracilis Correct answer.

Explanation

Lower-limb fibers for discriminative touch and conscious proprioception ascend ipsilaterally in the fasciculus gracilis to the nucleus gracilis in the medulla. The spinothalamic tract carries pain and temperature, and the spinocerebellar tract handles unconscious proprioception.

Question 9Neuroanatomy and Neurophysiology

A patient has a lesion of the right abducens nerve. Which finding is expected?

  1. Inability to abduct the right eye Correct answer.
  2. Right ptosis with a dilated pupil
  3. Inability to adduct the right eye
  4. Loss of sensation over the right forehead

Explanation

The abducens nerve innervates the lateral rectus, so its lesion prevents abduction of the ipsilateral eye and causes horizontal diplopia. Adduction depends on the oculomotor nerve, and ptosis with mydriasis indicates oculomotor involvement.

Question 10Neuroanatomy and Neurophysiology

Which structure separates the frontal lobe from the parietal lobe?

  1. Parieto-occipital sulcus
  2. Central sulcus Correct answer.
  3. Lateral sulcus
  4. Calcarine sulcus

Explanation

The central sulcus runs from the superior midline down toward the lateral sulcus and divides the frontal lobe anteriorly from the parietal lobe posteriorly. The lateral sulcus separates the temporal lobe, and the parieto-occipital and calcarine sulci lie more posteriorly.

Question 11Neuroanatomy and Neurophysiology

Blockade of voltage-gated sodium channels at the axon hillock primarily affects which process?

  1. Release of neurotransmitter from the terminal
  2. Reuptake of neurotransmitter
  3. Myelination of the axon
  4. Initiation of the action potential Correct answer.

Explanation

The axon hillock has a high density of voltage-gated sodium channels and serves as the trigger zone where the action potential is generated. Neurotransmitter release depends on calcium influx at the terminal, and myelination is a structural glial function.

Question 12Neuroanatomy and Neurophysiology

Which basal ganglia structure is the principal inhibitory output nucleus of the direct pathway to the thalamus?

  1. Subthalamic nucleus
  2. Ventral lateral thalamus
  3. Globus pallidus interna Correct answer.
  4. Putamen

Explanation

The direct pathway inhibits the globus pallidus interna, reducing its tonic inhibition of the thalamus and facilitating movement. The putamen is an input nucleus, the subthalamic nucleus belongs to the indirect pathway, and the thalamus is the target rather than the output source.

Question 13Neuroanatomy and Neurophysiology

A lesion of the right oculomotor nerve produces which combination of signs?

  1. Ptosis, mydriasis, and a downward-outward eye Correct answer.
  2. Loss of corneal reflex on the right
  3. Diplopia only on downward gaze
  4. Ptosis, miosis, and an upward-inward eye

Explanation

Oculomotor palsy paralyzes the levator palpebrae and most extraocular muscles while sparing the lateral rectus and superior oblique, leaving the eye down and out. Parasympathetic fibers on the nerve surface are also lost, causing a fixed dilated pupil.

Question 14Neuroanatomy and Neurophysiology

Which receptor type mediates the fast excitatory postsynaptic potential at the neuromuscular junction?

  1. Nicotinic acetylcholine receptor Correct answer.
  2. Alpha-adrenergic receptor
  3. GABA-A receptor
  4. Muscarinic acetylcholine receptor

Explanation

The nicotinic acetylcholine receptor is a ligand-gated cation channel whose opening produces a rapid depolarizing end-plate potential. Muscarinic receptors are G-protein coupled and slower, and adrenergic and GABA-A receptors respond to different transmitters.

Question 15Neuroanatomy and Neurophysiology

The cell bodies of primary sensory neurons carrying pain from the face are located in which structure?

  1. Trigeminal ganglion Correct answer.
  2. Nodose ganglion
  3. Geniculate ganglion
  4. Dorsal root ganglion of C2

Explanation

Facial pain is transmitted by the trigeminal nerve, whose pseudounipolar primary sensory neurons reside in the trigeminal (semilunar) ganglion. The geniculate and nodose ganglia belong to the facial and vagus nerves respectively.

Question 16Neuroanatomy and Neurophysiology

Which structure produces cerebrospinal fluid within the ventricular system?

  1. Arachnoid granulation
  2. Area postrema
  3. Pineal gland
  4. Choroid plexus Correct answer.

Explanation

The choroid plexus, located in the lateral, third, and fourth ventricles, secretes cerebrospinal fluid. Arachnoid granulations reabsorb fluid into the dural venous sinuses rather than producing it.

Question 17Neuroanatomy and Neurophysiology

A patient shows loss of pain and temperature sensation on the right side of the body with preserved touch and proprioception. Which tract is most likely damaged?

  1. Left dorsal columns
  2. Right medial lemniscus
  3. Right corticospinal tract
  4. Left lateral spinothalamic tract Correct answer.

Explanation

Pain and temperature fibers cross within the spinal cord and ascend in the contralateral spinothalamic tract, so a left-sided tract lesion produces right-sided sensory loss. Dorsal column lesions impair touch and proprioception instead.

Question 18Neuroanatomy and Neurophysiology

Which lobe contains the primary auditory cortex?

  1. Temporal lobe Correct answer.
  2. Occipital lobe
  3. Frontal lobe
  4. Parietal lobe

Explanation

Primary auditory cortex lies on the superior surface of the superior temporal gyrus within the transverse temporal gyri. The occipital lobe houses visual cortex, and the frontal and parietal lobes serve motor and somatosensory functions.

Question 19Neuroanatomy and Neurophysiology

Damage to the right middle cerebral artery territory most typically causes which deficit?

  1. Right leg weakness with urinary incontinence
  2. Cerebellar ataxia of the right arm
  3. Left face and arm weakness with left hemisensory loss Correct answer.
  4. Bilateral blindness

Explanation

The middle cerebral artery supplies the lateral convexity, including motor and sensory areas for the face and arm, so a right-sided stroke produces contralateral face and arm deficits. Leg weakness with incontinence suggests anterior cerebral artery involvement.

Question 20Neuroanatomy and Neurophysiology

Which ion influx directly triggers neurotransmitter release at the presynaptic terminal?

  1. Chloride
  2. Potassium
  3. Sodium
  4. Calcium Correct answer.

Explanation

Depolarization opens voltage-gated calcium channels, and calcium entry promotes fusion of synaptic vesicles with the presynaptic membrane. Sodium influx generates the action potential but does not directly trigger vesicle fusion.

Question 21Neuroanatomy and Neurophysiology

Which descending pathway primarily controls voluntary skilled movements of the distal upper limb?

  1. Tectospinal tract
  2. Vestibulospinal tract
  3. Reticulospinal tract
  4. Lateral corticospinal tract Correct answer.

Explanation

The lateral corticospinal tract originates from the motor cortex and synapses on lower motor neurons controlling distal muscles for fine voluntary movement. The vestibulospinal, reticulospinal, and tectospinal tracts mediate postural and reflex adjustments.

Question 22Neuroanatomy and Neurophysiology

A patient with a thalamic stroke develops spontaneous burning pain on the contralateral side. This finding is best explained by dysfunction of which structure?

  1. Ventral lateral nucleus
  2. Lateral geniculate body
  3. Ventral posterolateral nucleus Correct answer.
  4. Medial geniculate body

Explanation

The ventral posterolateral nucleus relays somatosensory input from the body, and its injury can cause central post-stroke pain. The ventral lateral nucleus is motor relay, and the geniculate bodies serve audition and vision.

Question 23Neuroanatomy and Neurophysiology

Which cranial nerve provides motor innervation to the muscles of facial expression?

  1. Trigeminal nerve (CN V)
  2. Glossopharyngeal nerve (CN IX)
  3. Facial nerve (CN VII) Correct answer.
  4. Hypoglossal nerve (CN XII)

Explanation

The facial nerve supplies the muscles of facial expression through its temporal, zygomatic, buccal, marginal mandibular, and cervical branches. The trigeminal nerve innervates muscles of mastication, and the hypoglossal nerve controls the tongue.

Question 24Neuroanatomy and Neurophysiology

Which brainstem structure contains the cell bodies of lower motor neurons for the facial muscles?

  1. Trigeminal motor nucleus in the pons
  2. Oculomotor nucleus in the midbrain
  3. Hypoglossal nucleus in the medulla
  4. Facial nucleus in the pons Correct answer.

Explanation

The facial motor nucleus lies in the caudal pons and its axons exit as the facial nerve to supply muscles of expression. The hypoglossal and oculomotor nuclei control the tongue and eye muscles respectively.

Question 25Neuroanatomy and Neurophysiology

Which property of myelinated axons accounts for the increased conduction velocity compared with unmyelinated axons?

  1. Continuous membrane depolarization along the entire axon
  2. Increased membrane capacitance
  3. Saltatory conduction between nodes of Ranvier Correct answer.
  4. Decreased axonal diameter

Explanation

Myelin increases membrane resistance and decreases capacitance, so the action potential regenerates only at nodes of Ranvier, jumping between them in saltatory conduction. This reduces the length of membrane that must depolarize and speeds conduction.

Question 26Neuroanatomy and Neurophysiology

At a resting membrane potential of about -70 mV in a typical neuron, which statement best describes the electrochemical driving forces acting on sodium and potassium ions?

  1. Sodium is driven inward by both gradients, while potassium is driven outward mainly by its chemical gradient. Correct answer.
  2. Both sodium and potassium are driven inward by combined chemical and electrical gradients.
  3. Both sodium and potassium are at equilibrium, so no net driving force exists at rest.
  4. Potassium is driven inward by both gradients, while sodium is driven outward mainly by its electrical gradient.

Explanation

At rest the interior is negative and sodium concentration is high outside, so both the electrical and chemical gradients push sodium inward. Potassium is concentrated inside, so its chemical gradient drives it outward even though the negative interior attracts it; the balance of these forces sets the resting potential.

Question 27Neuroanatomy and Neurophysiology

A lesion destroys the left dorsal columns and left dorsal root entry zone at the thoracic level. Which sensory finding is expected below the lesion?

  1. Loss of pain and temperature on the right with preserved vibration sense
  2. Loss of pain and temperature on the left with preserved vibration sense
  3. Loss of vibration and proprioception on the left with preserved pain and temperature Correct answer.
  4. Loss of vibration and proprioception on the right with preserved pain and temperature

Explanation

The dorsal columns carry ipsilateral fine touch, vibration, and conscious proprioception, so a left-sided dorsal column lesion impairs these modalities on the left below the lesion. Pain and temperature travel in the spinothalamic system, which crosses near the level of entry and ascends contralaterally, so they are unaffected by a dorsal column lesion.

Question 28Neuroanatomy and Neurophysiology

Which statement best describes the functional organization of the primary motor cortex (M1) with respect to movement control?

  1. It is purely sensory in function and receives no input from the premotor or supplementary motor areas.
  2. It contains a somatotopic map in which body regions are represented in proportion to their fine motor control. Correct answer.
  3. It encodes individual muscles rather than movements, with each cortical column driving a single muscle.
  4. It receives only ipsilateral input and controls muscles through direct monosynaptic connections to lower motor neurons.

Explanation

M1 has a somatotopic organization in which the hand, face, and tongue occupy disproportionately large areas because they require fine motor control. Cortical output reaches lower motor neurons mainly through polysynaptic pathways such as the corticospinal tract, and M1 is integrated with premotor and supplementary motor areas.

Question 29Neuroanatomy and Neurophysiology

Which neurotransmitter is released by postganglionic sympathetic neurons that innervate sweat glands and some blood vessels?

  1. Dopamine
  2. Norepinephrine
  3. Gamma-aminobutyric acid
  4. Acetylcholine Correct answer.

Explanation

Most postganglionic sympathetic neurons release norepinephrine, but those supplying sweat glands and some blood vessels are cholinergic and release acetylcholine. This exception is clinically relevant because it explains why sweating can be preserved or altered differently from other sympathetic functions.

Question 30Neuroanatomy and Neurophysiology

A patient has a lesion in the right internal capsule that interrupts the corticospinal fibers before they decussate. Which pattern of weakness is most consistent with this lesion?

  1. Weakness of the left face and left arm and leg Correct answer.
  2. Weakness of the right face and right arm and leg
  3. Weakness of the left arm and leg with sparing of the face
  4. Weakness of the right arm and leg with sparing of the face

Explanation

Corticospinal fibers in the internal capsule descend before crossing in the medulla, so a lesion above the decussation produces contralateral weakness. Because the internal capsule carries corticobulbar fibers as well as corticospinal fibers, the face is typically involved along with the arm and leg on the opposite side.

Question 31Instrumentation, Electronics, and Electrical Safety

When recording an EEG with a referential montage, which electrode site is most commonly used as the reference because it is relatively inactive during wakefulness?

  1. The occipital pole (O1/O2)
  2. Linked mastoids or earlobes (A1/A2) Correct answer.
  3. The active motor cortex (C3/C4)
  4. The frontal pole (Fp1/Fp2)

Explanation

Ear or mastoid references are chosen because they sit away from the cortical generators of interest and pick up comparatively little cerebral activity, so they provide a quiet baseline. Active cortical sites such as C3/C4 or O1/O2 would inject local EEG into every channel. Fp1/Fp2 are heavily contaminated by eye movement and blink artifact.

Question 32Instrumentation, Electronics, and Electrical Safety

In the international 10-20 system, which electrode lies at the midpoint between Fz and Cz on the midline?

  1. FCz Correct answer.
  2. Pz
  3. Cz itself
  4. Fpz

Explanation

The 10-20 system places electrodes at 10% or 20% intervals along measured arcs, and the midpoint between Fz and Cz falls at the FCz position used in the extended 10-20 (10-10) nomenclature. Pz lies posterior to Cz, and Fpz lies anterior to Fz. Cz is an endpoint, not the midpoint.

Question 33Instrumentation, Electronics, and Electrical Safety

An EEG technologist notices 60 Hz interference contaminating all channels. Which action most directly addresses the source of this artifact?

  1. Increasing the high-frequency filter setting
  2. Increasing the sensitivity (gain) of the amplifier
  3. Reducing electrode impedance and checking ground connections Correct answer.
  4. Shortening the time base on the display

Explanation

60 Hz artifact usually enters through high electrode impedance, a faulty ground, or nearby electrical equipment, so lowering impedance and verifying the ground path removes the source. Filter settings only mask the artifact while degrading the recording. Changing time base or gain does not affect the electrical pickup.

Question 34Instrumentation, Electronics, and Electrical Safety

What is the primary purpose of the ground electrode in a clinical EEG recording?

  1. To provide a common reference for all active electrodes
  2. To provide a return path that reduces electrical noise and protects the patient Correct answer.
  3. To measure skin temperature at the scalp
  4. To amplify the EEG signal before digitization

Explanation

The ground electrode gives interference currents a low-impedance return path and helps keep the patient at a safe potential relative to the equipment. It does not serve as the recording reference, which is a separate electrode. Amplification is done by the differential amplifier, not the ground.

Question 35Instrumentation, Electronics, and Electrical Safety

A differential amplifier records from an active electrode and a reference electrode. If a 60 Hz noise signal of equal amplitude and phase reaches both inputs, what happens at the output?

  1. The noise is doubled because both inputs contribute
  2. The noise is converted into a DC offset
  3. The noise is largely rejected because it is common to both inputs Correct answer.
  4. The noise is inverted and appears at half amplitude

Explanation

A differential amplifier responds to the difference between its inputs, so a signal identical in amplitude and phase at both inputs (common-mode) is largely cancelled. This common-mode rejection is why balanced electrode pairs reduce interference. Only the voltage difference between the inputs is amplified.

Question 36Instrumentation, Electronics, and Electrical Safety

Which measurement best verifies that an EEG electrode has acceptable contact with the scalp before recording begins?

  1. Measuring the electrode impedance in ohms Correct answer.
  2. Measuring the ambient room humidity
  3. Measuring the capacitance of the lead wire
  4. Measuring the electrode's DC offset voltage

Explanation

Electrode impedance reflects the quality of the skin-electrode interface; low, balanced impedances indicate good contact and reduce artifact. Capacitance, humidity, and ambient conditions are not direct measures of contact quality. DC offset can indicate polarization but is not the standard contact check.

Question 37Instrumentation, Electronics, and Electrical Safety

During an EEG, the technologist observes that the patient's heart rate appears as a regular rhythmic artifact in several channels. Which term describes this artifact?

  1. Muscle artifact
  2. Electrode pop
  3. Pulse artifact Correct answer.
  4. Sweat artifact

Explanation

Pulse artifact is a rhythmic slow wave that follows the heartbeat and appears when an electrode sits over a pulsating vessel. Muscle artifact is high-frequency and irregular, sweat artifact is a slow baseline sway, and electrode pop is a sudden sharp transient. Recognizing the rhythmic timing with the ECG helps confirm pulse artifact.

Question 38Instrumentation, Electronics, and Electrical Safety

A technologist needs to reduce slow baseline sway caused by sweating under the electrodes. Which adjustment is most appropriate?

  1. Decrease the paper speed or time base
  2. Raise the low-frequency (high-pass) filter setting Correct answer.
  3. Increase the sensitivity of the display
  4. Lower the low-frequency (high-pass) filter setting

Explanation

Sweat artifact is a very slow potential change, so raising the high-pass filter removes the slow sway while preserving faster EEG activity. Lowering the high-pass setting would admit even more slow drift. Sensitivity and time base alter display scaling but not the underlying slow potential.

Question 39Instrumentation, Electronics, and Electrical Safety

Which electrode type is most appropriate for recording EEG from a patient with a healing scalp wound who cannot tolerate adhesive paste?

  1. Subdermal needle electrodes placed in the wound
  2. A single referential electrode placed on the wound bed
  3. Disposable self-adhesive hydrogel electrodes placed on intact skin Correct answer.
  4. Standard paste-based disc electrodes over the wound

Explanation

Recording should avoid open wounds to prevent infection and contact problems, so self-adhesive hydrogel electrodes on intact skin are the safe choice. Needle electrodes carry infection and injury risk, and placing any electrode directly on a wound is contraindicated. Paste over a healing wound also risks contamination and poor contact.

Question 40Instrumentation, Electronics, and Electrical Safety

In a bipolar longitudinal (double banana) montage, a channel is labeled Fp1-F3. What does this label indicate?

  1. The voltage difference between Fp1 and F3 is displayed Correct answer.
  2. The sum of the voltages at Fp1 and F3 is displayed
  3. Fp1 is the reference for the entire montage
  4. F3 is the ground electrode for the channel

Explanation

In a bipolar derivation the channel displays the potential difference between the first (active) and second (reference) electrodes, here Fp1 minus F3. Bipolar chains compare adjacent electrodes along a line, so the label always denotes a difference, not a sum. Neither electrode acts as a global reference or ground in this derivation.

Question 41Instrumentation, Electronics, and Electrical Safety

Which electrical safety practice is required when a patient with EEG electrodes is also connected to other medical equipment?

  1. Ensure all equipment shares a common ground and is properly earth-referenced Correct answer.
  2. Use only battery-powered EEG amplifiers
  3. Disconnect the EEG ground to avoid ground loops
  4. Increase the amplifier gain to overcome leakage

Explanation

Shared, properly earth-referenced grounding keeps all devices at the same potential and limits leakage current through the patient. Removing the EEG ground or relying on battery power alone does not ensure a safe common reference. Raising gain does not reduce leakage current and may increase risk.

Question 42Instrumentation, Electronics, and Electrical Safety

What is the primary function of a differential amplifier's common-mode rejection ratio (CMRR) in EEG recording?

  1. It sets the sampling rate of the analog-to-digital converter
  2. It quantifies how well the amplifier rejects signals common to both inputs Correct answer.
  3. It determines the electrode impedance threshold
  4. It controls the brightness of the display

Explanation

CMRR expresses how strongly an amplifier suppresses common-mode signals such as 60 Hz interference relative to the differential EEG signal of interest. Higher CMRR means better rejection of interference. Sampling rate, impedance thresholds, and display brightness are governed by other components.

Question 43Instrumentation, Electronics, and Electrical Safety

A technologist observes an abrupt, sharp, isolated transient in a single channel that does not appear in adjacent channels. Which artifact is most likely?

  1. Alpha rhythm
  2. Electrode pop Correct answer.
  3. Pulse artifact
  4. Photoparoxysmal response

Explanation

Electrode pop is a sudden change in electrode contact that produces a sharp transient confined to the affected channel. Alpha rhythm is a physiologic posterior rhythm seen in multiple channels, pulse artifact is rhythmic and cardiac-timed, and photoparoxysmal responses are generalized epileptiform discharges triggered by light. A single-channel abrupt transient points to an electrode problem.

Question 44Instrumentation, Electronics, and Electrical Safety

Which factor most strongly influences the spatial resolution of an EEG recording?

  1. The number and spacing of electrodes on the scalp Correct answer.
  2. The brand of the recording software
  3. The color of the electrode leads
  4. The length of the patient's hair

Explanation

Spatial resolution depends on how densely electrodes sample the scalp; closer spacing and more electrodes allow finer localization of cortical sources. Lead color, software brand, and hair length do not determine the sampling density of the electric field. Higher-density arrays improve spatial discrimination.

Question 45Instrumentation, Electronics, and Electrical Safety

During an EEG, the technologist notices 50/60 Hz interference that disappears when the patient's bed is moved away from a nearby power supply. What was the most likely cause?

  1. Electromagnetic interference from nearby electrical equipment Correct answer.
  2. Muscle artifact from patient movement
  3. Sweat artifact from skin moisture
  4. Electrode pop from a loose lead

Explanation

Interference that vanishes when the patient is moved away from electrical equipment is characteristic of electromagnetic pickup from that equipment. Muscle, sweat, and electrode pop artifacts are generated at the patient or electrode interface and would not resolve simply by moving away from a power source.

Question 46Instrumentation, Electronics, and Electrical Safety

Which practice best minimizes the risk of electrical shock to a patient during an EEG study?

  1. Using ungrounded extension cords for convenience
  2. Inspecting leads and connectors for damage before each study Correct answer.
  3. Removing the ground electrode to break ground loops
  4. Increasing the amplifier gain to reduce current flow

Explanation

Routine inspection of leads and connectors detects damaged insulation or exposed conductors that could deliver current to the patient. Removing the ground or using ungrounded cords increases shock risk, and gain settings do not limit leakage current. Prevention relies on intact, properly grounded equipment.

Question 47Instrumentation, Electronics, and Electrical Safety

A scalp electrode is placed over a pulsating superficial artery, and a rhythmic slow wave appears in that channel. Which corrective action is most appropriate?

  1. Increase the high-frequency filter to remove the wave
  2. Add a second reference electrode at the same site
  3. Move the electrode slightly off the vessel Correct answer.
  4. Increase the sensitivity to make the wave clearer

Explanation

Pulse artifact arises when an electrode overlies a pulsating vessel, so relocating the electrode away from the artery removes the source. Filtering or gain changes do not eliminate the mechanical cause, and duplicating the reference does not address the vessel. Repositioning is the definitive fix.

Question 48Instrumentation, Electronics, and Electrical Safety

Which statement correctly describes the relationship between electrode impedance and recorded EEG signal quality?

  1. Lower, balanced impedances generally improve signal quality and reduce artifact Correct answer.
  2. Impedance has no effect on the recorded signal
  3. Higher impedances always improve the signal-to-noise ratio
  4. Impedance only affects the color of the display

Explanation

Low and balanced electrode impedances reduce thermal noise and interference pickup, improving signal quality and common-mode rejection. High impedance increases susceptibility to artifact and noise. Impedance does not affect display color and is not irrelevant to signal quality.

Question 49Instrumentation, Electronics, and Electrical Safety

A technologist is asked to reduce high-frequency muscle artifact in a channel without distorting the underlying EEG. Which filter adjustment is most appropriate?

  1. Increase the display sensitivity
  2. Raise the high-frequency (low-pass) filter setting
  3. Lower the low-frequency (high-pass) filter setting
  4. Lower the high-frequency (low-pass) filter setting Correct answer.

Explanation

Muscle artifact is high-frequency activity, so lowering the low-pass (high-frequency) filter attenuates it. Raising the low-pass setting would admit more fast activity. The high-pass filter controls slow activity, and sensitivity affects display scale rather than frequency content.

Question 50Instrumentation, Electronics, and Electrical Safety

Why are silver/silver chloride (Ag/AgCl) electrodes widely used in clinical EEG?

  1. They provide a stable, low-noise electrode-skin interface Correct answer.
  2. They generate the EEG signal themselves
  3. They eliminate the need for a ground electrode
  4. They are the only electrodes that can record alpha rhythm

Explanation

Ag/AgCl electrodes are nonpolarizable and provide a stable half-cell potential with low noise, which improves recording quality. They are not required for alpha rhythm, do not replace the ground, and do not generate EEG signals. Their stability makes them a standard choice.