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A&P module 4 CNS > 4.6 EEG > Flashcards

4.6 EEG Flashcards

1
Q

Electroencephalogram (EEG)

A

a graphical representation of the electrical activity of part of the cerebral cortex recorded from electrodes placed on the scalp and a record of the fluctuations in the electrical activity of hundreds or thousands of neurons in the area underlying a recording electrode

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2
Q

From the pial surface of the cortex to the underlying white matter, the cerebral cortex is organized into ___ layers

A

6

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3
Q
  • An EEG reflects electrical activity only in the most ___ layers
A

superficial

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4
Q

Where are the pyramidal cells found that generate the EEG?

A

layers III and V

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5
Q

Excitatory neurons whose axons project to other areas of the brain or spinal cord

A

Pyramidal cells

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6
Q

Pyramidal cells have ____ that are oriented parallel to each other and perpendicular to the surface of the cortex

A

apical dendrites

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7
Q

The configuration of the apical dendrites helps focus the ____ they generate in a common direction, pointing up towards the scalp electrodes found on the electrode cap that the patient wears

A

electrical activity -

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8
Q

The electrical activity recorded by an EEG is the result of ____ current flow produced by postsynaptic potentials (EPSPs or IPSPs) in the apical dendrites

A

extracellular

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9
Q
  • The summed ionic currents in thousands of dendrites, all oriented in the same direction, produce a potential called a ____
A

field potential

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10
Q

EPSP’s and IPSP’s are initiated on the apical dendrites via ___ nerve fibers from either the thalamus or contralateral cortex

A

afferent

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11
Q

The type of rhythm is defined by the ____

A

wave frequency

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12
Q

Characteristic of a state of relaxed wakefulness (awake with eyes closed) May be thought of as the “default” frequency when comparing anesthetized to non-anesthetized patients
8-13 Hz

A

Alpha waves

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13
Q

are seen in an alert, attentive, working brain

13-30 Hz

A

Beta waves -

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14
Q

Daydreaming, relaxed, eyes closed 4-7 Hz

A

Theta waves

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15
Q

dreamless sleep

0.5-4 Hz

A

Delta waves

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16
Q

With brain waves, frequency and amplitude are usually _____

A

inversely proportional

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17
Q

When EEG activity is at a low frequency and a large amplitude, it is referred to as ____; this indicates that many cortical neurons are firing slowly and simultaneously

A

Synchronized

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18
Q
  • The rhythmic pattern of the EEG waveform reflects cyclical waves of EPSPs reaching the ___ from the ____
A

cerebral cortex, thalamus

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19
Q
  • During deep sleep or anesthesia, complex circuits in the thalamus produce alternating depolarization and hyperpolarization in ____
A

thalamocortical neuron

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20
Q

The thalamus isn’t relaying any specific sensory information to the cortex, it’s just acting like a

A

“pacemaker”

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21
Q

Thalamus “pacemaker”
Periodic bursts of action potentials from the thalamus synchronize pyramidal cell firing and show up on the EEG as ______

A

large, rhythmic, slow waves

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22
Q
  • During normal wakefulness, multiple sensory inputs (vision, hearing, touch, etc.) desynchronize thalamic neurons, interrupting the synchronized firing of thalamocortical neurons
A

desynchronized -

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23
Q

Incoming EPSPs from sensory pathways cause thalamic neurons to fire in a pattern reflective of those specific sensory stimuli.
This pattern of firing reflects increased wakefulness and is seen as a _____ pattern in the EEG (i.e., high frequency, low amplitude)

A

desynchronized -

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24
Q

In general, as a patient “goes to sleep” with general anesthesia, EEG waves become ___ in amplitude and ___ in frequency (i.e., more synchronized)

A

larger, slower -

25
Q

Methods have been developed to use computers to convert the analog EEG signal into digital data and to mathematically manipulate the data

A

Bispectral IndexTM (BISTM) -

26
Q

The most widely known proprietary form of processed EEG, the ____, integrates three modes of signal analysis

A

Bispectral IndexTM (BISTM) -

27
Q

Values ____ indicate deep to very deep hypnosis

A

< 50 to < 20

28
Q

Values < 60

A

indicate unconsciousness

29
Q

Values < 70

A

indicate low probability of recall

30
Q

values> 90

A

BISTM values > 90 indicate an awake/alert state

31
Q

Some professional societies in anesthesia have recommended routine use of BIS monitoring to allow the anesthetist to titrate the amount of anesthetic agent to the needs of the patient and to prevent patient ___

A

awareness during surgery

32
Q

are the electrical manifestation of the response of the CNS or PNS to an artificial, external stimulus

A

Evoked Potentials (EP)

33
Q

To improve the signal-to-noise ratio, EP’s are evoked via ____, and the recorded signal is averaged over time

A

repetitive peripheral stimuli -

34
Q

The _____ response occurs at a constant time after the stimulus and with predictable polarity, whereas other electrical activity occurs randomly

A

evoked

35
Q
  • A computer averages the signals resulting from many stimuli; as a result, random electrical activity averages to ____ and repetitive signals are emphasized
A

zero

36
Q

If EP’s are recorded from the brain, the same ___ that are used for recording the EEG are employed. If the EP is recorded from the spinal cord or spinal nerves, ____ are placed near the spinal cord or nerves

A

scalp electrodes, superficial or needle electrodes

37
Q
  • Recorded EP waveforms are evaluated for both ____ and then compared with control EP recordings
A

amplitude and latency

38
Q
  • ____ is the time measured from the application of the stimulus to the onset or peak of the EP; it’s mainly a reflection of the speed of nerve conduction
A

Latency -

39
Q

___ is the voltage of the recorded response to the stimulus; it chiefly reflects the number of neurons in a pathway that responded to the stimulus

A

Amplitude

40
Q

By convention, deflections below baseline are labeled ___ and those above the baseline are labeled ___

A

positive (P)

negative (N)

41
Q

Standard waveforms are designated by their direction of deflection (N or P) and latency in ___

A

milliseconds

42
Q
  • Type of MEP poorly tolerated by awake subjects, may cause seizures
A

Transcranial electrical stimulation

43
Q

The most commonly used EP, recorded after electrical stimulation of a superficial peripheral nerve with cutaneous or needle electrodes

A

Somatosensory evoked potentials (SSEP) -

Recordings are usually made somewhere along the peripheral nerve, over the cervical spinal cord, and over the contralateral parietal lobe cortex

44
Q

SSEP’s assess the ____ from the peripheral nerve, through the spinal cord and brain stem, to the cortex

A

somatic sensory pathways

45
Q

i. Correction of scoliosis
ii. Spinal cord decompression
iii. Spinal fusion
iv. Procedures on the thoracic or abdominal aorta (a major source of blood for the spinal cord)
v. Brachial plexus exploration after injury

A
  • Examples of procedures that warrant SSEP monitoring:
46
Q

Recorded after repetitive clicks or tones delivered through foam ear inserts, recorded from the earlobe of the stimulated ear and at the top of the head

A

Brain stem auditory evoked response (BAER) -

47
Q
  • BAER indicated for use during procedures near the auditory pathway and procedures in the posterior cranial fossa in which brainstem function could be compromised, a characteristic series of ___ occurs within ____, each originating from an anatomical point along the brain stem auditory pathway
A

7 waves, 10 msec -

48
Q
  • Recorded after stimulating the retina with flashes of light from LEDs imbedded in soft goggles, recorded from the occipital, parietal and central scalp
A

Visual evoked response (VER) -

49
Q

Visual evoked response (VER) -

Warranted for surgical procedures in the:

A

orbit
adjacent to the optic nerve or tracts
or near the pituitary gland -

  • VER monitors function of the retina, optic nerve and tract, optic radiations, and occipital cortex
50
Q

Assess the function of the motor cortex and descending motor pathways, stimulus: applied to specific parts of the primary motor cortex (precentral gyrus)

A

Motor evoked potentials (MEP)

51
Q
  1. Somatosensory evoked potentials (SSEP)
  2. Brain stem auditory evoked response (BAER)
  3. Visual evoked response (VER)
A

Three types of Sensory EPs

52
Q

Type of MEP where discharge of a strong electromagnet near the skull over the motor cortex is better tolerated but less specific

A

Magnetic stimulation -

53
Q

Recording of MEP happens from the ____ using percutaneous epidural electrodes

A

lateral column of the contralateral spinal cord -

54
Q

More often with MEPs, compound, muscle action potentials are recorded using cutaneous electrodes positioned over a ___

A

superficial muscle -

55
Q

General effects of anesthetic drugs: most drugs used for anesthesia increase ___ (slow nerve conduction) and decrease ___ (desensitize neurons)

A

EP latency, amplitude -

56
Q

The concern with EP monitoring is that an anesthetic drug can produce a change in sensory or motor EPs that could be mistaken for a ____

A

surgically induced change (a whoopsie) -

57
Q
  • Three physiologic factors influencing EPs:
A

Temperature
a. Hypothermia increases latency and decreases amplitude
b. Hyperthermia decreases amplitude; at 42°C, SSEP’s are abolished
Blood gases: hypoxia decreases EP amplitude

58
Q

Blood pressure: decreases in blood pressure below levels of CNS autoregulation (intrinsic mechanisms for maintaining blood flow in the face of fluctuating blood pressure) can decrease_______ in EP’s without changes their latency

A

amplitude

A&P module 4 CNS (7 decks)

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