Epilepsy and EEG Flashcards
What is a seizure?
A temporary disruption of brain function due to abnormal excessive neuronal activity.
What is epilepsy?
The chronic condition of repeated seizures.
What are the different types of seizures?
Focal onset.
Generalised onset.
Unknown onset.
Where do focal onset seizures originate?
Small groups of neurons called the seizure focus.
How does a focal onset seizure typically begin?
Begins with jerking in the right hand, progressing to clonic movements of the entire right arm.
What happens when a focal onset seizure progresses?
The person will enter a tonic or clonic phase.
What happens during a tonic phase?
The person loses consciousness, their muscles stiffen, and they may fall to the ground.
What happens during a clonic phase?
Muscles rhythmically contract and relax, causing jerking movements in the face, arms, and legs.
What is an aura?
Unprovoked and often vivid sensations, such as fear, a rising feeling in the abdomen, or a particular odour.
Where do generalised onset seizures originate?
Both hemispheres are involved from the onset.
What are the two types of generalised onset seizures?
Motor (grand mal).
Non-motor (petit mal).
Are generalised onset seizures preceded by an aura?
No.
Are focal onset seizures preceded by an aura?
Sometimes.
Who typically experience non-motor generalised onset seizures?
It is a typical absence seizure in children.
What happens during a non-motor generalised onset seizure?
Staring.
Sudden cessation of all motor activity.
Loss of awareness but not posture.
What happens during a motor generalised onset seizure?
Begins with a tonic phase lasting around 30 seconds.
Evolves into a clonic phase lasting around 1-2 minutes.
What happens during the post ictal phase of a motor generalised onset seizure?
The person is sleepy and disorientated.
What is an unknown onset seizure?
A seizure that cannot be identified because the person was alone when it happened or there is inadequate information to make the identification.
What does NEAD stand for?
Non-epileptic attack disorder.
What happens during a NEAD?
A person experiences symptoms similar to those of epilepsy but without any abnormal activity in the brain.
What is another term for a NEAD?
Psychogenic non-epileptic seizure.
What is the cause of a NEAD?
The causes are not fully understood but it may be associated with anxiety, depression and personality disorders.
What does EEG stand for?
Electroencephalogram.
What is an EEG?
A set of field potentials as recorded by multiple electrodes on the surface of the scalp.
Why is the amplitude of EEG signals much smaller than the voltage changes in a single neuron?
The signal is distorted by the filtering and attenuation caused by the intervening layers of tissue and bone.
What does an EEG primarily represent?
Slower voltage changes across the cell membrane.
Why is synaptic activity in pyramidal neurons the principle source of EEG activity?
Pyramidal neurons are the major projection neurons in the cortex and their apical dendrites are orientated perpendicular to the cell surface.
Explain the 10-20 system.
21 electrodes are placed on the surface of the scalp using the nasion and inion as reference points.
Using the reference points, the skull perimeters are measured in the transverse and median planes.
The perimeters are divided into 10% and 20% intervals for the electrode locations.
3 other electrodes are placed on each side equidistant from the neighbouring points.
What is the nasion?
The delve at the top of the nose, level with the eyes.
What is the inion?
The bony lump at the base of the skull.
Why are generalised onset seizures driven by thalamocortical circuits?
These seizures disrupt normal brain activity in both hemispheres simultaneously.
How does seizure activity spread?
Intense activity in the seizure focus can cause the electrical activity to spread to other brain regions, typically following the same axonal pathways as normal cortical activity.
Which pathways can become involved in seizure spread?
Thalamocortical, subcortical and transcallosal pathways.
What is the 3-Hz spike-and-wave pattern?
The characteristic EEG pattern of a non-motor generalised onset seizure.
Where in the brain is the 3-Hz spike-and-wave pattern observed?
In all cerebral areas abruptly and simultaneously.
