NB505
Terms
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- What is a seizure
- Excessive and/or hypersynchronous abnormal activity in the brain
- What is epilepsy?
- A disorder where the seizures are chronic and recurrent.
- What is a convulsion?
- Uncontrolled contractions of voluntary muscles.
- Give some examples of possible positive and negative symptoms of a seizure.
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Positive - jerking of a limb
Negative - amnesia - What percentage of the human population may be affected by seizures?
- 0.5 to 1%
- What is the meaning of paroxysmal?
- A sudden, sharp electrical event, e.g. a paroxysmal deporlarization shift.
- What is the meaning of ictal?
- A full seizure event. From the latin work ictus = strike.
- What is the meaning of interictal?
- Between seizures, usually refers to time.
- What is an interictal "spike" from an EEG point of view and when recorded from a single neuron?
- A sharp wave in EEG lasting 50-150 msec. When recorded from a single neuron, also known as a "paroxysmal depolarization shift."
- What is the meaning of postictal and what is its alternate name?
- Period after a seizure. Usually called postictal depression.
- Why is the postictal period sometimes called the postictal depression?
- Patients appear lethargic, confused or restless. Can be seconds to hours.
- What is an aura?
- Awareness or conscious sensation that precedes onset of certain types of seizures, e.g. strange odor, intense fear.
- What are automatisms?
- Stereotyped, involuntary motor activities, e.g. lip smaching, that often precede a seizure.
- What are the two basic types of seizures?
- Partial and generalized.
- Where do partial seizures begin in the brain? What is an alternate name for these?
- Begin in a focal cortical area, i.e. "focus" or epileptogenic zone. Often also called a "focal" seizure.
- What are the two types of partial seizures?
- Simple partial seizures and complex partial seizures.
- What are the characteristics of simple partial seizures and what will be observed in an EEG?
- Affect motor or sensory functions w/o disrupting consciousness. EEG seizure activity occurs in specific motor or sensor areas of neorcortex.
- What are the characteristics of a complex partial seizures?
- Consciousness lost or distrubed. Often begins with an aura and automatisms, and followed by amnesia and a period of confusion.
- Where is a complex partial seizure likely to be located when viewing the EEG?
- Often localized to temporal cortex.
- What is an alternate name for complex partial seizures?
- Psychomotor, temporal lobe or limbic seizures.
- What is a generalized seizure?
- Onsent is bilaterally symmetrical in the brain.
- What are the two types of generalized seizures?
- Non-convulsive and convulsive.
- What is an older name for a non-convulsive generalized seizure?
- petit mal
- What age group are non-convulsive generalized seizures seen?
- Children and adolsescents.
- What is likely to be seen during a non-convulsive generalized seizure?
- Last 2 to 10 seconds. Impaired consciousness associated wtih rolling of the eyes, blinking.
- What is typically seen in an EEG with a non-convulsive generalized seizure?
- Shows "3/sec spike and wave".
- What are alternative names for a convulsive generalized seizure?
- Grand mal or tonic-clonic.
- What is likely to be observed during a convulsive generalized seizure?
- Patients fall to the ground in rigid extension for 15-20 seconds (tonic phase), frequently loose bladder and bowel control. This blends into clonic phase: rhythmic limb contractions for 20-30 sec.
- What will the EEG look like for a convulsive generalized seizure?
- 10-20 Hz high-ampltude activity during the tonic phase; groups of polyspikes separated by quiet intervals during clonic phase.
- What could be an alternative outcome of a complex partial seizure?
- Can spread bilaterally to cause a secondarily generalized seizure.
- What is status epilepticus?
- A medical emergency characterized by the recurrence of seizures at a rate so rapid that consciousness does not return to normal.
- What is the epidemiology/causes of seizures?
- Seizures can occur in normal brain - hypoxia, hypoglycemia, poisons, etc.
- What is the epidemiology/causes of epilepsy?
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Causes - Mechanisms unknown although know:
- Hereditary aspect - increased tendency for certain types of epilepsy
- Injury - head trauma, stroke, and turmors. - What are the basic mechamisms of seizure activity and epileptogenesis?
- ???
- What are interictal discharges?
- Paroxysmal depolarization shift (PDS) - sudden, large-amplitude and sustained deporlarization that is synchronized in many neurons (30 mv, 70-200 msec).
- How can interictal discharges be experimentally induced?
- By blocking synaptic inhibition and by other methods.
- What are the mechanisms of synchrony?
- Chemical synapses, electrical interactions, and ionic changes.
- What are four cellular changes that are hypothesized to occur in epilepsy?
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Less inhibition through loss of inhibitory interneurons?
Less inhibition through dormant inhibitory interneurons.
More synaptic excitation.
Synaptic reorganization - possible new recurrent excitatory circuits. - What are the two general approaches to controlling epilepsy?
- Medication and resective surgery.
- What are some of the antiepileptic druges (AEDs) and how do they work?
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Barbituarates and benzodiazepines - augment GABA-mediated inhibition.
Phyenytoin - blocks high-frequency firing of action potentials. - Where is surgery most effective?
- Primarily for intractable complex partial seizures in temporal lobe (hippocampus).
- What is an EEG measuring?
- They detect the synchronized activity of large numbers of cells; such signals are called field potentials. Because of the time scale - hundreds of ms - they do not measure action potentials per se.
- What common cortical circuit results in an electrical response that is similar to a PDS (paraoxysmal depolarization shift)?
- It is quite common to see a pyramidal cell with feedback through an inhibitory interneuron. Hence we will see an EPSP (depolarization) followed in time by an IPSP (hyperpolarization).
- What are the two major stages in a paraoxysmal depolarization shift?
- First, we see a sudden depolarization of the membrane potential that can last from 50 to 150 ms. At the end of this pulse will be a hyperpolarization wave.
- What are the major channels involved in a paraoxysmal depolarization shift and its recovery?
- Initially, AMPA channels will start the depolarization of the membrane. NMDA channels will typically turn on next (these are slower and last longer). There also may be voltage-gated calcium channels that turn on. One the feedback inhibitory circuit is activated, GABA-A channels will turn on in the pyramidal cell. There are often other K channels involved.
- What are some of the things that can happen during a simple partial seizure?
- Can be a clonic or tonic activity or a sensory perception, e.g. weird sensation.
- What are some of the properties of complex partial seizures?
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. Not so much where they occur
. Key - Disruption/loss of consciousness
. Learning/memory can occur (hippocampus) => amnesia - When do complex partial seizures often occur?
- Going into or out of sleep.
- What are two general properties of absence vs. tonic-clonic seizures? Concerns broad terms for times of stages.
- short event/quick recovery vs. long event/slow recovery
- What EEG phenomina is seen in most epileptic patients?
- Interictal spikes
- What is the effect of penicillin being introduced into the brain of a mouse?
- Blocks GABA-A receptors => PDS and large EPSPs.
- One mechanism of epilepsy relates to chemical synapses. What is happening?
- Many pyramidal cells are interconnected. If inhibition stops => they can all fire at once.
- One mechanism of epilepsy relates to electrical interaction. What does this mean?
- Gap junctions tie together interneurons