Evoked Potential Practice Exam

Averaging improves the signal to noise ratio by the square root of the number of epochs averaged. This means that as the number of epochs averaged increases, the signal to noise ratio improves by the square root of that number. Averaging helps to reduce the random noise in the data and enhance the underlying signal, leading to a clearer and more accurate representation of the desired information.

The N13 of the median nerve somatosensory evoked potential is generated in the cervical spinal cord. This is because the N13 component represents the electrical activity generated when the sensory information from the median nerve reaches the cervical spinal cord. The brachial plexus is responsible for the transmission of the nerve signals from the upper limb to the spinal cord, but it is not where the N13 component is generated. The medial lemniscus is a pathway in the brainstem that carries sensory information to the thalamus, but it is not involved in the generation of the N13 component. The primary somatosensory cortex is responsible for processing sensory information, but it is not where the N13 component is generated.

The correct answer is 10%. When adjusting the amplifier sensitivity based on the number of averaging rejection, the goal is to improve the signal to noise ratio. This means that a certain percentage of the total number of stimulations will be rejected. In this case, the approximate percentage is 10%, indicating that 10% of the stimulations will be rejected in order to achieve the desired improvement in signal to noise ratio.

A smaller surface area of stimulating electrodes results in a higher current density. This is because the same amount of current is being delivered through a smaller area, leading to a higher concentration of current. This can be beneficial in certain applications where a more focused or intense stimulation is desired.

The accuracy of electrode placement is most critical for near field responses. Near field responses refer to the electrical activity that is detected close to the site of stimulation or recording. In order to accurately measure and interpret these responses, the electrodes need to be placed precisely and in close proximity to the target area. Any slight deviation in electrode placement can lead to inaccurate recordings and misinterpretation of the results. Therefore, ensuring the accuracy of electrode placement is crucial for obtaining reliable and meaningful near field responses.

The input impedance of the amplifier should be higher compared to electrode impedance because a higher input impedance ensures that the amplifier does not load or disturb the signal coming from the electrodes. It allows for better signal transfer and minimizes any distortion or loss of signal during amplification. A higher input impedance also helps in maintaining the accuracy and fidelity of the amplified signal.

Subdermal electrodes are placed beneath the skin and have a higher impedance compared to other types of electrodes. This higher impedance makes them more susceptible to noise interference, which can affect the accuracy of the recorded signals. Noise can be caused by various factors such as muscle activity or electromagnetic interference, and the high impedance of subdermal electrodes makes them more prone to picking up these unwanted signals.

Neurofibromatosis is most likely to be associated with bilaterally prolonged I-III intervals in brainstem auditory evoked potential. This is because neurofibromatosis is a genetic disorder that affects the growth and development of nerve cells, including those involved in auditory processing. The prolonged I-III intervals indicate a delay in the transmission of auditory signals from the ear to the brainstem, which is consistent with the neurological abnormalities seen in neurofibromatosis.

The absence of all waveforms in a lower extremity somatosensory evoked potential can be caused by various factors such as technical problems, peripheral nerve lesions, and insufficient stimulation intensity. However, cortical lesions do not cause this absence of waveforms.

P14 is the least affected by anesthetic agents during intraoperative monitoring of somatosensory evoked potentials. This is because P14 is an early component of the evoked potentials and is generated in the primary somatosensory cortex. It is less influenced by the effects of anesthesia compared to the other waves, such as N27, N37, and P37, which may be more affected by the anesthetic agents.

The decussation of the pyramids refers to the crossing over of nerve fibers in the medulla oblongata, which is located at the cervial medullary junction. This crossing over is important for the coordination of motor functions in the body. The other options, such as the pons, cerebellum, and diencephalon, are not specifically associated with the decussation of the pyramids.

The cochlea generates the EcochG EP response.

The correct answer is 1.4 msec because wave I of the auditory evoked potential is the earliest wave that can be detected in response to an auditory stimulus. It represents the activation of the auditory nerve fibers and occurs approximately 1.4 msec after the stimulus onset. Therefore, it cannot appear before this time.

The correct answer is "Averaging starts after stimulus onset" because in order to average the responses to a stimulus, the averaging process needs to begin after the stimulus has been presented. If the averaging were to start before the stimulus onset, it would include unrelated or baseline activity, which would not accurately reflect the response to the stimulus. Therefore, it is necessary for the averaging to begin after the stimulus onset to capture the specific response to the stimulus.

Partial field stimulation is the correct answer because a W-shaped pattern reversal visual evoked potential (VEP) is typically indicative of a partial field defect. Partial field stimulation involves presenting visual stimuli to specific areas of the visual field, allowing for the detection and characterization of localized visual field defects. This technique can help identify the specific area of the visual field that is affected and provide valuable information for diagnosis and treatment planning. Electroretinography, flash stimulation, and steady state stimulation are not typically used to resolve a W-shaped pattern reversal VEP.

The central conduction time in median nerve somatosensory evoked potentials is measured between N13 and N20. This is because N13 represents the arrival of the sensory input at the lower medulla, while N20 represents the arrival of the sensory input at the cerebral cortex. By measuring the time between these two points, we can assess the conduction speed of the sensory signals along the median nerve pathway.

The appropriate stimulus intensity for recording SEP (Somatosensory Evoked Potential) is just above the motor threshold. This means that the intensity should be slightly higher than the minimum level required to elicit a motor response. By setting the stimulus intensity just above the motor threshold, it ensures that the nerve is being adequately stimulated without causing excessive discomfort or pain to the individual. This allows for accurate recording of the somatosensory response without any interference from motor responses.

Collodion is a liquid adhesive commonly used in medical applications to secure electrodes to the scalp during electroencephalography (EEG) procedures. However, it does not provide a conducting material between the electrode and scalp. Collodion's primary function is to enhance the adhesion of the electrode to the skin, ensuring it stays in place during the procedure. To establish electrical conductivity, a conductive gel or paste is typically applied between the electrode and the scalp. Therefore, it is important to be aware that collodion alone does not facilitate the conduction of electrical signals between the electrode and the scalp.

Reversal of the click polarity can alter the cochlear microphonic. The cochlear microphonic is a small electrical potential generated by the hair cells in the cochlea in response to sound stimulation. Reversing the polarity of the click can change the direction of the electrical current flowing through the hair cells, which in turn can alter the amplitude and waveform of the cochlear microphonic response.

The brain stem is the correct answer because the posterior fossa is a part of the skull that houses the brain stem. The brain stem is responsible for many vital functions such as controlling breathing, heart rate, and blood pressure. It also serves as a pathway for nerve fibers traveling between the brain and spinal cord. The other options, knee, cauda equina, and temporal lobe, are not located in the posterior fossa.

The brainstem auditory evoked potential (BAEP) waveforms refer to the electrical activity generated by the auditory nerve and brainstem in response to sound. The given answer, 3-6 months, suggests that all components of the BAEP waveforms reach their adult configuration by this age. This means that the auditory system in infants develops and matures during the first few months of life, and by 3-6 months, it resembles the patterns seen in adults. This is an important milestone in auditory development as it indicates the establishment of normal auditory functioning.

The most sensitive setting is 10 microvolts per division. This is because microvolts are smaller than millivolts, so a smaller change in voltage can be detected. Therefore, with a setting of 10 microvolts per division, the device will be able to detect and display smaller voltage changes compared to the other options.

When the distance between a patient and a pattern generator is reduced by one-half, the angle at the eye subtended by each check is increased two times. This is because the angle subtended by an object at the eye is inversely proportional to the distance between the object and the eye. As the distance is reduced by half, the angle at the eye will be doubled.

The latency-intensity function findings for this ear suggest that there is conductive hearing loss. This means that there is a problem with the transmission of sound from the outer or middle ear to the inner ear. It could be caused by issues such as blockage, fluid in the middle ear, or problems with the bones of the middle ear. This type of hearing loss typically results in a decrease in the overall volume of sound.

The amplitude of an evoked potential depends on the number of cortical or subcortical generators simultaneously activated. This means that the more generators that are activated at the same time, the larger the amplitude of the evoked potential will be. The other options, such as the velocity of neural impulses or the synchrony of neural impulses, do not directly affect the amplitude of the evoked potential. The number of normal neural generators sequentially excited may have an impact, but it is not the primary factor determining the amplitude.

The P100 waveform is generated in the striate cortex. The striate cortex, also known as the primary visual cortex or V1, is located in the occipital lobe of the brain. It is responsible for processing visual information received from the eyes. The P100 waveform refers to a positive deflection in the electroencephalogram (EEG) that occurs approximately 100 milliseconds after the onset of a visual stimulus. This waveform reflects the neural activity in the striate cortex, specifically the processing of early visual information such as basic features and orientation of objects.

The most appropriate bandpass for pattern reversal visual evoked potentials is 1-200 Hz. This range allows for the detection of the specific frequencies associated with pattern reversal visual stimuli, while filtering out any unwanted frequencies that may interfere with the measurement.

The optic disc is the correct answer because it is a part of the eye that does not contain any photoreceptor cells, making it a blind spot in our visual field. It is the area where the optic nerve exits the eye and connects to the brain, transmitting visual information. This area lacks the ability to detect light, resulting in a blind spot in our vision. The other options, such as lens, fovea, and macula, are all important structures in the eye but do not represent the blind spot.

The resting membrane potential refers to the electrical potential difference across the cell membrane when the cell is at rest. This potential difference is maintained by the active transport of ions, particularly sodium and potassium ions, across the membrane. The value of -70mV indicates that the inside of the cell is negatively charged compared to the outside. This negative charge is essential for various cellular processes, including the transmission of nerve impulses and the regulation of ion channels.

When resistors are connected in series, the total resistance is the sum of the individual resistances. In this case, the total resistance is 4 ohms + 2 ohms = 6 ohms. According to Ohm's Law (V = I * R), the current (I) is equal to the voltage (V) divided by the resistance (R). Therefore, the current across each resistor is 6 volts / 6 ohms = 1 amp.

Digital filters do not produce a phase shift. Unlike analog filters such as the 60Hz, notch, and passive RC filters, which can introduce a phase shift in the recorded evoked potentials, digital filters process the signal in the digital domain and do not alter the phase of the signal. Therefore, when recording evoked potentials, digital filters are preferred over analog filters to avoid any phase distortion in the recorded data.

Stimulus rates higher than 20 per second may reduce amplitudes of all BAEP peaks except for peak V.

The impedance of cup electrodes is lower than needle electrodes because of their size. Cup electrodes have a larger surface area compared to needle electrodes, which allows for better contact with the skin and reduces the impedance. This larger surface area allows for more efficient electrical signal transmission, resulting in lower impedance.

In a brainstem auditory evoked potential, decreasing click intensity refers to reducing the loudness of the auditory stimulus. This decrease in intensity should not have any effect on the timing between the peaks or the intervals between them. Therefore, the interpeak intervals will remain unchanged.

Proprioception deficit is the most closely correlated symptom with somatosensory evoked potential abnormalities. Somatosensory evoked potentials (SEPs) are electrical signals generated by the nervous system in response to sensory stimuli. Proprioception refers to the sense of body position and movement, which is mediated by the somatosensory system. Abnormalities in SEPs can indicate dysfunction in the somatosensory pathways, leading to deficits in proprioception. Vertigo, tinnitus, and hemiparesis are not directly related to somatosensory processing, making proprioception deficit the most likely symptom associated with SEPs abnormalities.

Long pulse duration and high repetition rates are the parameters causing most concern for patient safety in somatosensory electrical stimulation. This is because long pulse durations can lead to tissue damage and discomfort for the patient, while high repetition rates can cause muscle fatigue and overstimulation. Therefore, it is important to carefully monitor and adjust these parameters to ensure the safety and comfort of the patient during the stimulation process.

Wave V is usually the most prominent peak after 5.5 msec. This suggests that there are other waves before Wave V that occur within the time frame of 4.7 msec to 5.5 msec. However, after 5.5 msec, there are no waves that are more prominent than Wave V.

The central conduction time in posterior tibial nerve somatosensory evoked potentials is measured between the L3 and P37 electrodes.

The maximum leakage current should be 100 uA because it falls within the range of acceptable values for leakage current. Leakage current refers to the small amount of current that flows through an electrical device even when it is supposed to be in an off state. In this case, a maximum leakage current of 100 uA indicates that the device allows a small amount of current to flow, but it is still within the acceptable limits.

The identification of wave V of the brainstem auditory evoked potential may require decreasing stimulus intensity. This is because wave V is the last and largest wave in the evoked potential, and it represents the response from the brainstem. By decreasing the stimulus intensity, it becomes easier to isolate and identify the specific waveform associated with wave V. This allows for a more accurate assessment of the auditory pathway and can help diagnose any abnormalities or disorders.

Conductive hearing loss is caused by a problem in the outer or middle ear that prevents sound from reaching the inner ear. Brainstem auditory evoked potentials (BAEPs) are used to assess the function of the auditory pathway from the ear to the brainstem. In a patient with conductive hearing loss, the problem lies in the outer or middle ear, and the auditory pathway up to the brainstem is unaffected. Therefore, the interpeak latencies, which represent the time it takes for the auditory signal to travel from one point in the pathway to another, will be normal.

Paraparesis refers to a partial paralysis of the lower extremities. It is characterized by weakness or loss of voluntary movement in the legs, but not a complete loss of function. This condition can be caused by various factors such as spinal cord injuries, nerve damage, or diseases affecting the motor system. Unlike paraplegia, which is a complete paralysis of the lower body, paraparesis allows for some degree of movement and sensation in the affected areas.

The stimulus used in a brainstem auditory evoked potential study is a click with a peak acoustic power in the range of 2000 to 4000 Hz. This range is chosen because it corresponds to the frequency range of human speech, which is important for assessing auditory processing and speech perception abilities. By using a stimulus in this frequency range, researchers can evaluate the brain's response to speech sounds and determine if there are any abnormalities or deficits in auditory processing.

The correct answer is patient age. Pattern reversal visual evoked potential (PRVEP) is a diagnostic test used to assess the function of the visual pathway. It measures the time it takes for the brain to process and respond to visual stimuli. Patient age can significantly affect the latency of PRVEP, with older individuals generally having longer latencies compared to younger individuals. This is due to age-related changes in the visual system, such as decreased retinal and neural function, which can lead to slower processing of visual information. Ambient light, ocular dominance, and refractive errors of less than 20/20 may have some impact on PRVEP latencies, but patient age is the most significant factor.

The recommended somatosensory electrode derivation to best record the N13 response is C5s-Epc. This is because the N13 response is a somatosensory evoked potential that originates from the contralateral primary somatosensory cortex. Therefore, the electrode placement should be on the contralateral side (C5s) to the stimulation site, which is typically the median nerve. The reference electrode (Epc) is commonly placed on the earlobe or mastoid. This configuration allows for optimal recording of the N13 response.

An amplification factor of 500,000 means that the input signal is multiplied by 500,000. Therefore, a 1uV brainstem auditory evoked potential waveform will be amplified to 500,000 * 1uV = 500,000uV = 0.50V.

A pattern reversal visual evoked potential is a test used to measure the electrical activity in the brain in response to visual stimuli. The fovea is the central part of the retina responsible for sharp, central vision. In order to stimulate the fovea effectively, a check size that is not too small or too large should be used. A check size of 15 minutes of arc would be the most appropriate because it is neither too small nor too large, allowing for optimal stimulation of the fovea.

The correct answer states that positivity at the vertex produces a downward deflection. This means that when there is a positive electrical signal at the vertex (the top of the head), it will result in a downward deflection on the recording. This polarity convention is commonly used when recording brainstem auditory evoked potentials, where changes in electrical activity in response to auditory stimuli are measured.

The theoretical maximum frequency resolution is determined by the Nyquist-Shannon sampling theorem, which states that in order to accurately represent a signal, the sampling rate should be at least twice the highest frequency component of the signal. In this case, if the signal averager samples every millisecond, the sampling rate is 1000 samples per second. According to the Nyquist-Shannon theorem, the theoretical maximum frequency resolution would be half of the sampling rate, which is 500 Hz.

The approximate amplitude resolution of a 10-bit digitizer can be calculated by dividing the total range of the digitizer (plus or minus 5uV) by the number of possible values (2^10). Therefore, the approximate amplitude resolution would be 10uV / 1024 = 0.01uV.

The most likely condition shown in the diagram is chronic otitis media. This is because chronic otitis media is an inflammation or infection of the middle ear that can cause fluid accumulation and damage to the structures of the ear. The diagram may show signs such as fluid-filled middle ear, thickening of the eardrum, or other characteristic findings associated with chronic otitis media. Pontine glioma, midbrain infarct, and acoustic neuroma are unrelated conditions and would not typically present with the findings seen in the diagram.

The fastest component of a complex waveform is near 100Hz, which means that the waveform has a frequency of 100Hz. Dwell time refers to the amount of time spent at each data point in a waveform. In order to accurately capture the fastest component of the waveform, the dwell time should be less than or equal to the period of the waveform. The period of a waveform with a frequency of 100Hz is 1/100 seconds, which is equal to 10 milliseconds. Therefore, the most appropriate dwell time would be 5 milliseconds, as it is less than the period of the waveform.

The signal to noise ratio is a measure of the strength of the desired signal compared to the background noise. In this case, the signal has a voltage of 10uV and the noise has a voltage of 50uV. To calculate the signal to noise ratio after 100 averaged responses, we need to consider the effect of averaging on the noise. Averaging multiple responses can help reduce the effect of random noise, resulting in a higher signal to noise ratio. Therefore, after 100 averaged responses, the signal to noise ratio would be improved, resulting in a ratio of either 2:1 or 5:1.