Seizures Flashcards
seizures
transient alteration of behaviour due to abnormally excessive + synchronous neuronal activity
abnormal neuronal firing
epilepsy
disorder of brain function characterized by periodic and unpredictable occurrence of seizures
symptomatic: known cause
unsymptomatic: no known cause - genetic?
normal neuronal firing
neurons fire asynchronously → spread of electrical activity controlled by refractory period + surround inhibition
action potential
cell membrane at rest = -70mV
concentration gradietn generates membrane potential
reach threshold = Na+ influx
reversal of potential = K+ efflux
reduction of potential → hyperpolarization - refractory period
surround inhibition
mechanism that focuses neuronal activity in CNS
overlapping primary afferents - central is closest to point of stimulation = strongest
primary afferents synapse onto inhibitory interneurons - synapse onto surrounding afferents
a neuron activating strongly inhibits its neighbours
Mechanism of Seizures
initiation, propagation, termination
initiation
high frequency bursts of action potentials
hypersynchronization of a neuronal population
sustained neuronal depolarization → burst of action potentials driven by Ca2+ influx through NMDA receptors
action potential releases glutamate which binds to AMPA and fires to dislodge Mg2+ from NMDA = amplification of excitatory effect
propagation
normally prevented by hyperpolarization and surround inhibition but overcome by sufficient activation
increased extracellular K+ blunts hyperpolarization
Ca2+ accumulation in presynaptic terminals = increased NT release
depolarization activates NMDA receptor to increase Ca2+ influz and increase neuronal activation
termination
seizures gradually resolve spontaneously
loss of ion gradients
depletion of ATP
depletion of NT
activation of inhibition (GABA)
status epilepticus
a seizure that lasts more than 5 minutes
life threatening
over excitation - neuronal death
postictal period
5-30 minutes after seizure
drowsiness, confusion, depression/anxiety
increased inhibition response to excitation
classes
where they initiate + how widely they propagate
focal seizures
localized + don’t propagate far
simple: retain consciousness
complex: lose consciousness
jerking activity, automatisms
can become generalized
generalized seizures
propagation across entire brain
loss of consciousness (complex) + without warning
tonic-clonic: sustained contraction of muscles followed by alternating contraction and relaxation
myoclonic: bried shock like contraction of muscles
non-convulsive seizures
absence seizure: abrupt onset of impaired consciousness - lose consciousness but don’t fall
atonic seizures: sudden loss of muscle strength - fall but don’t lose consciousness
