Neurophysiology Flashcards
What is the general function of the following lobes
Frontal, Parietal, Occipital, Temporal
Frontal Lobe - problem solving/higher function
Parietal Lobe - Spatial perception
Occipital Lobe - Vision
Temporal Lobe - Language and Information processing
How many layers does the cerebral cortex have
6
What type of neurons generate the EEG
Pyramydal
What layers of the cortex are pyramidal neurons located, and what layer is their cell body location
Cell body located in layer 5 and project to layer 1
What orientation are pyramidal neurons
Vertical
What charge will a cell be if it has an EPSP
Negative
What is the resulting charge of the scalp surface and thus the deflection on the EEG going to look like if there is an EPSP near the cell body of the pyramidal neurons
EPSP arriving to the cell body will make that end of the neuron negatively charged. This makes the top of the neurons positively charged.
Positive discharge on EEG is a NEGATIVE (downward) deflection
What ions are usually responsible for postsynaptic potentials
Na+/Ca2+
How long are EPSP
50ms
What is an example of a neurotransmitter that causes EPSP
NMDA and AMPA
What is an example of a neurotransmitter that causes IPSP
GABA
What is the thalamus role in generating EEG
The neurons that excite the pyramidal neurons come from the thalamus. So is the thalamus isn’t working, then there will be no excitation of pyramidal neurons and no EEG created
Where are the pacemaker cells of neuronal intrinsic rhythm located
In the thalamus
What is paroxysmal depolarizing shifts and what does this cause in the morphology of the EEG
These are sustained EPSPs that generate epileptiform spikes
What 3 anatomical landmarks are located at the beginning of measuring a head for EEG
Nasion (bridge of nose)
Inion (bump at the back of skull)
Preauricular points (middle of ears)
What is the minimum and ideal impedance of EEG electrodes
Ideally <5kΩ, minimum <10 KΩ
What is the maximum impedance difference we can have between a pair of electrodes in EEG
<5kΩ
What is the effect on artefact is the impedance of the electrode is high
High artefact
When measuring the head in the sagittal plane, what is the value of the interval between each electrode
10% of total sagittal plane length between nasion and first electrode, and inion and first electrode.
20% interval between the rest of the electrodes
When measuring the head in the horizonal plane, what is the value of the interval between each electrode
10% of total sagittal plane length between nasion and first electrode, and inion and first electrode.
20% interval between the rest of the electrodes
What amplifier is used in EEG machinery
Differential amplifiers
What is the usual sensitvity control set at in EEG machines
7-10uV
What would be the consequence of having the amplitude sensitivity control too high
There would be a decreased sensitivity to the signal
What is the sweep speed of EEG
30mm/s
What three filters are commonly used in EEG machines
High frequency filter, low frequency filter and notch filter
What is the role of the high frequency filter in an EEG and what frequency is the cut off usually set too
Used to remove high frequencies from the signal. Usually set to remove anything above 70Hz
What is the role of the low frequency filter in an EEG and what frequency is the cut off usually set too
Used to remove low frequencies from the signal. usually set to remove anything lower then 0.5Hz
What is the minimum sampling rate needed for EEG
256Hz
What is the Time Constant in EEG
Describes how much low frequency singal the high pass filter removes
Want a higher time constant when trying to detect slow waves pathologically (coma) and a lower time constant in areas of high artectact (sweating/movement)
What is the notch filter of an EEG usually set at
50Hz
What is bipolar longitudinal montage useful for seeing
Symmetry between left and right side of the brain
What is the transverse montage useful for viewing
To determine if activity has temporal/[parasagittal activity
How does the electrode relationships differ between bipolar montage and reference montage
Bipolar montage involved pairs of electrodes whereas reference montage involved one common reference electrode all the scalp electrodes are in refeerence too
In a reference montage where is the reference electrode ideally placed
In an area that is electrically neutral or produces minimal interference
What is a expected EEG response to hyperventilation
Increased slow wave activity - increase in theta and delta wave appearence
What is the method of hyperventilation during EEG
3-4 breaths per 10 seconds for 3 minutes
What is hyperventilation a well known activator of
Absence seizure waveforms (3Hz/s spike wave)
What is the expected EEG activity of someone with photic stimulation
Epileptic abnormalities: high amplitude generated spike waves
What are the two most photosensitive seizures
Generalised tonic-colonic seizures
Juvenile Myoclonic Epilepsy
What is the effect of sleep deprivation on EEG
Increases the diagnostic yield of EEG and increases generalised discharges
What electrodes are eye blinking seen in on EEG
-vs deflection in Fp1 and Fp2
What frequency of artefact is expected during electrical interference
50Hz
Frequency of alpha waves
8-13Hz
Frequency of beta waves
> 13Hz
Frequency of theta waves
4-8Hz
Frequency of delta waves
0.5-1Hz
What is the dominant EEG wave in awake adults
Alpha
What does phase reversal tell us
The common electrode between the two phases is the location of electrical activity
When you describe EEG activity, what 3 factors should you always include
frequency, location and symmetry
What area of the brain should an EEG be dominant in a healthy adult
Posterior
What is MU rhythm and how can it be blocked
Type of alpha wave, but is usually asymmetrical and can be blocked by activating the collateral hand
What is a Lambda wave, what electrodes are they found in
Triangle ‘sail’ waves
Found over O1, O2, P3, P4, P5 (posterior region)
Seen with eyes are open
What cortex are lambda waves usually evoked from
Opitcal cortex
What happens to alpha waves when the eyes are opened in a healthy adult
The alpha waves should stop
What are vertex sharp waves and what sleep stage are they seen in
Seen in stage 1 sleep as you transition in stage 2
High altitude, V shaped waves, predominately seen in Cz
What are K complexes and what sleep stage do these occur in
Sharp vertical downwards reflections with and increase and slow deflection
Stage 2 sleep
What 4 changes to the EEG are expected in a coma patient
Increase in slow wave activity (delta/theta)
Triphasic Complexes
Suppression bursts
PLEDS
Delta Brush
What are PLEDS a indicator of
represent focal neurological damage
What does triphasic complexes indicate on EEG
Characteristic of a wide range of encephalopathy due to hypoxia
PLEDS and triphasic complexes will occur in a brain during what state
Coma
What is delta brush on an EEG
Superimposed higher frequency activity, associated with anti-NDMA encephalitis
What is the major change in an EEG throughout childhood
The amount of slow wave activity decreases
What are two specific EEG features specific to children
Alpha subharmonic and posterior slow waves
EIDEE (Otahara Syndrome)
- What is the age onset
- What type of seizures so they have
- EEG pattern
Onset < 3 months
Frequent seizures, usually just one type
Burst suppression pattern
IESS (Wests Syndrome)
- Age onset
- Type of seizure that occurs
- EEG characteristics
Onset 1-12 months
Epileptic spasms
EEG is characteristic of spasm (prominent EMG burst of <2sec) and hypsarrhythmia (chaotic, high amplitude, multifocal spikes)
What is the effect of brain structure and neurological condition of people with self-limited epilepcy
No structural or neurological impairment usually
At what stage in life do self-limited seizures tend to stop
Puberty
SeLECTS
- Age of onset
- Type of seizures
- EEG characteristics
Onset 4-10 years
Seizures are brief, usually nocturnal and involve the mouth and face a lot. Cant speak but can understand
EEG has centro-temporal spikes
SeLEAS
- Age onset
- Type of seizure
- EEG characteristic
Onset 3-6 years
Seizure frequency is low, focal autonomic seizure with or without impaired awareness
EEG - posterior-temporal spikes, particularly in occipital lobe
COVE
- Age of onset
- Type of seizure
- EEG characteristics
Onset 8-9 years old
Seizures mostly visual
EEG has occipital spikes
Lennox Gastaut Syndrome
- Age of onset
- Type of seizure
- EEG characterisitcs
Onset 18 months - 8 years
Tonic seizures + one other seizure type.
EEG - slow spike patterns (<2.5Hz) in awake state, in sleep there is paroxysm fast activity
What are the effects on cognitive and neurological development in developmental encephalopathies
Development is usually impaired
Landau Kleffner Syndrome
- Age of onset
- Characteristic behavioural change
- EEG characteristics
Onset 2-12 years
Language and motor regression
EEG - in wakefulness EEG is normal, in sleep there is high frequency spike wave discharges
Lennox Gastaut Syndrome, Landau Kleffner Syndrome, EIDEE and IESS are all what types of epilepsy syndromes
Developental Encephalopathies
SeLECTS, SeLEAS and COVE are all what type of epilepsy syndromes
Self-limited
Childhood absence epilepsy
- Age of onset
- Seizures + trigger
- EEG characteristics
Onset 4-10 years old
Seizures multiple times a day, 3-20 seconds long, severe loss of awareness. Triggered by hyperventilation.
2.5 - 5Hz generalised spike wave, clean on onset, clean on offset
What is the effect on cognitive development with those with genetic generalized epilepsy syndromes
No change in development
Juvenile absence epilepsy
- Age of onset
- Seizures
- EEG characteristics
9-13 onset
Seizures less then daily, complete loss of consciousness. Hyperventilation triggers
EEG not as neat at childhood absence epilepsy - irregular discharges in background, 3-5.5Hz generalized spike wave
Juvenile Myoclonic Epilepsy
- Triggered by
- Seizures
- EEG characteristics
triggered by sleep deprivation
Seizures can be tonic or tonic-conic or absent seizures
EEG - bilateral polyspike discharged and not as regular as childhood epilepsy
What is the most common epilepsy syndrome with adolescent and adult onset
Juvenile Myoclonic Epilepsy
What is a seizure
Sudden alteration of behaviour due to temporary change in the electrical functioning of the brain
What is the ILAE definition of epilepsy
Two unprovoked seizures 24 hours apart, or one unprovoked seizure and a probability of further seizures of <60% after two unprovoked seizures
What two factors are associated with seizure relpase
Presence of cerebral lesion
Epileptiform abnormalities in a EEG
What is idiopathic epilepsy
A group of epileptic disorders believed to have strong genetic basis.
No structural abnormalities
What are 4 treatment appraches to epilepsy
Anticonvulsant medication
Vagal nerve stimulation
Ketogenic diet
Surugry
What observations do we rely on in an EEG to show epilepsy due to the low chance of observing a clinical seizure
Inter-ictal discharges (IEDs)
Specific paroxysmal discharge
How can we increase the yeild of detecting IEDs in EEG
Sleep deprivation
What is a focal aware seizure
A seizure that has started in one small region of the brain, a person is fully aware but may not be able to talk/respond
What are the symptoms of temporal lobe seizures
Patients tend to report sensation of deja vu
Automatisms (repetative movements)
What is a Jacksonian March Seizure
Frontal lobe seizure - arises from primary motor cortex (causes clonic twitching with LOC)
For seizures arising in the supplementary motor cortex, what is the symptoms
Deviation of the head and eyes associated with tonic elevation of the contralateral arm
What sort of seizures often occur out of sleep
Frontal lobe seizures
How come frontal lobe seizures can be hard to see on EEG
The front lobe seizures often arise in an area of the brain which is relatively inaccessible to scalp EEG
Due to the large muscle movements that occur in frontal lobe seizures, the muscle signals can distort the EEG
Symptoms of occipital lobe seizures
Blindness, visual field loss, visual misconception, visual hallucination
What hemispheres of the brain does a generalised seizure usually affect
Both
Explain the two phases of a tonic-colonic seizure
Tonic - stiffening of muscles, eyes open, tounge/cheek biting
Colonic - jerking movements, incontinence
What is the well known activator of absence seizures in EEG
Hyperventilation
What is the characteristic EEG pattern seen in absence seizures
3Hz/s spike wave
What is status epilepticus
Condition in which prolonged/recurrent seizures accompany persistent altercation of the neurological state
What is the ILAE definition of status epilepticus
Seizure with 5 minutes or more of continuous clinical and/or electrographic activity OR
recurrent seizure activity without recovery between seizures
What is ictal-interictal continuum
Discharges that are epileptiform and continuous but dont fufill the criteria for an EEG seizure
What is an example of an ictal-interictal continuum
Triphasic complexes (initial small negative sharp discharges followed by large positive sharp discharges with subsequent negative wave)
What two conditions can triphasic complexes indicate
Hepatic enchephalopathy
Uremic encephalopathy
What are PLEDS
Defined as unilateral focal spikes or sharp waves occuring at an approximately regular interval
What does PLEDS tell us about the state of the cerebellum
That it is intact
What condition can PLEDS indicate
Herpes Simplex Enchephalitis
How do you measure the nerve conduction velocity when doing a nerve conduction study
Distance between the two stimulating points / (proximal latency - distal latency)
What measurements/methods are used by physiologists in IOM
Evoked potentials (motor and somatorsensory)
Direct cortical and subcortail stimulation
Triggered EMG
What horn in the spinal cord is connected to motor nerve
Anterior horn
What nerves, sensory or motor, have ganglia and what are these ganglia called
Sensory nerves are connected to dorsal root ganglia
What are the most vulnerable sensory fibres too pathology
Large myelinated fibres
What is the amplitude of the AP determined by
The strength of the AP (number of axons propagating the signal)
If there is a decrease in amplitude of the nerve conduction study, what does this suggest
Loss of axons
If there is a decrease in velocity of the nerve conduction study, what does this suggest
Loss of myelin
What do F waves tell us about on nerve conduction study
Tell us about the conduction up at the level of the spinal cord
What do H waves in nerve conduction studies tell us
This is the sensory response when the motor nerve is activated (comes slightly after the motor wave as the sensory fibre has to go across a synapse)
What nerve is measured in carpel tunnel nerve conduction studies
Median nerve
What are some typical findings on a nerve conduction study for carpel tunnel
Prolonged latency in motor and sensory nerves
Normal ulnar nerve conduction rules out other conditions
What is an example of focal neuropthy
Carple Tunel
What is the most common presentation of motor nerve study patients
Weakness
What are some syptoms of people have a nerve condution study
Tingling/numbness, burning or shooting pain, loss of sensation, muscle weakness, coordination problems
What is polyneuropathy
Symmetrical loss of neural fibres
What sort of sensations so A-alpha and A-beta fibres sense
Mechanical - mechanoreceptors
What sort of sensory result will there be in neuropathy of small fibres
Pain and burning
What is Lillian Barry Syndrome
Infection that affects the nerves and causes respiratory failure
What is an example of demylinating neuropathy of motor nerves
Lillian Barry Sydnrome
What pathway is pain signalling transmitted within
Somatosensory
Pain signalling is facilitated by what type of neurotransmitters
Excitatory - substance P, glutamate, CGRP
Allodyina
Painful response to non-noxious stimuli
Where does descending neural inhibition of pain originate from
PAG
What part of the spinal cord does descending pain inhibition synapse too
Dorsal Horn
What fibres inhibit pain in the gate control theory
A-beta
What neurotransmitter is released in gate control theory of pain inhibtion
GABA
What is neuropathic pain
Pain arisen as a direct consequence of lesion of disease affecting the somatosensory system
What are some causes of neuropathic pain
Peripheral origin - nerve injury, neuropathy, entrapment syndromes
Central origin - stoke, spinal cord injury, parkinsons
Where in the somatosensory cortex map is the upper limbs located
Mid line
Where is the auditory cortex located
Just above the ears
What is averaging and how does this help in evoked potentials
This averages out the noise in a signal so we are able to observe the small signals that are produced in evoked potential studies
Where is the stimulating and recording areas in a somatosensory evoked potential study
Stimulate a peripheral nerve
Record over brain, spine and limb
What is the commonly evoked nerve in lower limb evoke nerve studies
Posterior tibial nerve (ankle)
What is the commonly evoked nerve in upper limb evoke nerve studies
Median Nerve (wrist)
Prolongation of latency in evoked potentials usually indicates what
Delayed signal transmission often due to demyelination or nerve damage
What positions are used to record spinal cord responses in upper limb and lower limb evoked potential study
Upper limb (N13) - cervical spine (C5)
Lower limb (N22) - Lumbar spine (L1-L3)
What electrodes are used for measuring scalp signals in upper and lower evoked potential studies
Upper - C3 or C4 (contralateral to the stimulated side)
Lower - Cz midline
What are the reference electrodes used in evoked potential studies
Fz (foorehead) or Ear (A1/A2)
What 3 electrodes are used for visual evoked potentials (VEP)
Occipital scalp - O1, O2, Oz
What are the location of the recording electrodes of brainstem auditory evoked potentials
Vertex (Cz) - midline scalp
What is the p100 in visual evoked potential
The primary positive peak occurring around 100ms
A prolonged p100 latancy in visual evoked potentials is common in what pathology
Multiple Sclerosis
What is the N135 in visual evoked potentials
The large positive deflection following p100 in visual evoked potentials
What is the N75 in visual evoked potentials
The large positive deflection before p100 in visual evoked potentials
What 2 types of stimuli are used in visual provoked potentials
Pattern reversal and flash stimulation
What are symptoms of multiple sclerosis
Bad peripheral vision, pressure in eyes, sports in vision
What is the key waveform we are interested in brainstem auditory evoked potentials
V - Represents conduction through the central visual pathways to the visual cortex.
What are changes expected to see in EEG of coma patients
Generalised slowing (increase in delta and theta activity)
Burst suppression pattern
Triphasic Waves
Isoelectric Line
Epileptiform Activity
What are favourable prognosis EEG signs in coma
Active EEG (spindles, alpha)
Responsiveness
What are unfavourable prognosis EEG signs in coma
Suppression bursts and isoelectric line
What is the difference between spike waves and sharp waves in epileptiform
Spike waves last less than 70 ms
Sharp waves last longer then 70 ms
List 4 different types of epileptiform
Spike waves
Sharp Wave
Polyspikes
PLEDS
What things do we need to consider in a surgury environment when doing IOM
Effects of anaestaia
Poor baselines at times
Lots of noise in theatre
What is the advantage of MEP’s that makes them good to use in a surgury setting
They have a large signal-to-noise ratio so they can record the MEPs without averaging
What type of stimulation is used in MEPs in IOM
High frequency multiple pulse anodal stimulation
What is mode is used for motor MEPs in IOM
Monopolar
Where to the best MEPs come from during IOM and why
Fingers and toes due to the large cortical representation of these areas
What is the delay in the NMJ due too
Biochemical properties that enable the AP to travel across the synapse - including neurotransmitter release, diffusion, receptor activation and muscle membrane depolarisation which are inherently slower processes then a signal flowing through a single nerve fibre
What nerves are not Mylinated
Autonomic Nerves
What physiological event does P100 in VEP signify
Represents conduction through the central visual pathways to the visual cortex.
What would be the pathology associated with a decrease or absence in VEP
Optic Neuritis (damage and loss of axons in optic nerves)
