Cortical Electrical Recordings Flashcards
define primary
genetic
define idiopathic
unknown
define symptomatic
known underlying cause: developmental, degenerative, inflammatory, infectious, neoplastic, traumatic
define reactive
metabolic, nutritional, or toxic cause
define reflex epilepsy
sensory stimuli triggers an episode
define seizure
physical findings and/or changes in behavior that result from abnormal electrical activity in the brain
what effects can a seizure include
motor, sensory, autonomic, or psychic effects
define epilepsy
abnormal activity in cerebral cortex that results in a seizure
what is an epileptic seizure a clinical sign of?
abnormal forebrain disorder
what is status epilepticus?
seizure lasts 5 min or longer within a few days or 2 seizures within 24 hours
what are cluster seizures?
increased frequency of seizures within a few days or 2 seizures w/in 24 hours
what are the 3 phases of epileptic seizure?
prodome
ictus
post-ictal period
what happens during the prodome period?
pre-ictal period; abnormal behavior may occur hours before ictus
what happens during the ictus period?
seizure lasting 1-2 minutes, characterized by loss of consciousness and alteration
what happens during the post-ictal period?
return to normal or altered behavior - recovery period
what does EEGs measure?
collective electrical activity of these neurons in cortex
how is the cortex organized?
layers and columns
what is in the layers of the cortex?
Layer 1 - glia cells and dendrites of neurons in lower layer
Layers 2-6 - stellate cells relieve afferents from brainstem sensory neurons, pyramidal cells send axons to other parts of cortex
Layer 4 - receives thalamic inputs
Layer 5 - motor efferent neurons to SC
Layer 6 - projections to basal ganglia and thalamus
what are the major cell types of the cortex?
pyrimidal neurons
stellate neurons
glial cells
what is a focal seizure
originates in localized portion of cortex = seizure focus
what is a generalized seizure
involves both hemispheres of brain
originates in thalamus with abnormal activity in thalamocortical circuit
what is a secondary generalized seizure?
focal seizure start locally and spreads to rest of cortex -> generalized seizure
what contributes to membrane potential and creation of action potentials?
ions
ion channels
pumps
pH
what are the two kind of ion channels responsible for inhibitory and excitatory activity
voltage-gated channels
ligand-gated channels
which ligand-gated channels causes hyperpolarization and which cause depolarization?
GABA - hyperpolarization
AMPA & NMDA - depolarization
when might elipesy channelopathies occur?
mutations to various channels -> enhanced excitability or loss of inhibition
what is a paroxysmal depolarization shift?
sudden, large, long depolarization
what does a paroxysmal depolarization shift (PDS) lead to?
train of AP
recurrent high frequency bursts of AP
what causes the depolarization phase in PDS?
calcium and glutamate channel activation
what receptors mediate and maintain initial and sustained depolarization in PDS
initial - AMPA
sustained - NMDA
what causes the hyper polarization phase in PDS?
termination of PD -> Cl and K flux via GABA receptors
how do PDS remain localized in healthy NS?
recurrent of axons affected -> active inhibitory interneurons -> dampens spread of seizure to neighboring cells
what happens when surround inhibition breaks down?
seizure spreads
when can a seizure spread?
neurons die - loss in inhibitory interneurons
channelopathies - disorders in ion channels -> high Na, Ca & low K
what is detected on the EEG?
how do electrodes on the surface of the scalp work?
detect transient electrical fields when individual neurons depolarize
what is detected in practice from the electrodes?
average signal of all the depolarizing neurons in the cortex under the electrode on the scalp
what will a positive voltage change do to the EEG?
downward reflection
what will a negative voltage change do to the EEG?
upward deflection
what are EEGs useful in?
identifying and classifying epilepsies
localizing lesion in cortex
sleep studies
legal determination of brain death
what do the electrodes over the occipital lobe measure?
electrical activity related to vision
how do alpha and beta waves look in awake EEG?
alpha - regular high amplitude sweeping pattern
beta - irregular and low amplitude
is this patient awake or asleep
awake
what are the characteristics of a sleeping slow wave EEG?
delta waves - slow wave sleep
what is paradoxial sleep characterized by?
low amplitude, irregular EEG
what EEG is similar to the awake eyes closed EEG?
sleeping EEG
what EEG is similar to the awake eyes open EEG?
paradoxical sleep
what is this the EEG of?
slow wave sleep
what is this an EEG of?
paradoxical sleep
what are sleep spindles in the sleeping EEG?
bursts of activity from the thalamus to the cortex
what are K complexes?
extensive activities in the primary sensory corticles
what can an EEG determine?
focal vs generalized seizure
part of cortex affected
how seizure spreads through cortex over time
Can intracranial EEGs provide future ability to forecast seizures?
yes
how does flashing lights induce seizures
photosensitive epilepsy - brain responds excessively to certain visual stimuli
what explains rhodesian ridgebacks sensitivity to myoclonic jerks and photosensitive epilepsy?
4-bp deletion in DIRAs gene
