NB3-5 - Paroxysms and Synaptic Plasticity Flashcards
What is the leading theory on how memory is stored?
Memories are believed to be stored as engrams which are some kind of biophysical or biochemical change encoded amongst populations of neurons. These engrams have not been directly observed.
What are the 3 general types of amnesias?
- Failure to produce engrams
- Loss of engrams
- Failure in accessing stored engrams
What are the two general types of synaptic plasticity?
Long Term Potentiation (LTP) - high frequency electrical stimulation leads to a stronger signal response between two neurons for a period of time
Long Term Depression (LTP) - low frequency electrical stimulation leads to a weaker signal response between two neurons for a period of time
In which tissues does LTP and LTD occur?
Hippocampus
Cortex
Cerebellum
Describe how LTP and LTD actually occur at the CA1 hippocampal synapse?
- Presynaptic neuron releases glutamine which binds to NMDA and AMPA receptors
- AMPA receptors let in Na+ which depolarizes the terminal, allowing NMDA to let in Ca++
- Ca++ influx leads to protein kinase actiavtion
- Protein kinases then phosphorylate intracellular AMPA receptors, promoting their delivery to the membrane
This is how the postsynaptic response becomes intensified. If the presynpatic neuron fires less frequently, the opposite happens (LTD).
List the important differences in how LTP and LTD occur in the hippocampus and cerebellum.
- In the hippocampus, the GluR1 subunit of AMPA is phosphorylated to promote its transport to the membrane (LTP).
- In the cerebellum, the GluR2 subunit of AMPA is dephosphorylated to promote its transport to the membrane (LTP)
B
Define and explain how the following terms are related:
Paroxysms
Seizures
Convulsions
Epilepsies
Epileptogenesis
- Paroxysm - sudden onset burst of neuronal activity (may include seizures)
- Seizure - pathological synchronization of neuronal activity
- Convulsions - motor manifestations of seizure
- Epilepsy - chronically hightened susceptibility to seizures
- Epileptogenesis - transformation of a non-epileptic brain into an epileptic brain
What is status epilepticus? Why is it dangerous?
Seizures typically self-terminate after about 1-2mins. If they continue past 5min then the patient is in status epilepticus. This can cause excitotoxicity which can permanently damage the CNS.
What are the three classes of seizures? What are the subclasses?
- Generalized
- Primary generalized - extensive bilateralized cellular synchronization (consciousness lost)
- Seconday generalized - a primary generalized seizure that began as a focal seizure (consiousness lost at transition)
- Focal (aka partial seizures) - arises form a localized pathological population of cells (consciousness typically remains but awareness may be impaired). May transition to a generalized seizure
- Unknown onset
What are the common features of a primary generalized seizure?
- Family History
- Early onset
- Usually generalized from onset
- Unconsciousness throughout episode
List the major types of primary generalized seizures and their typical manifestations.
- Absence - often brief, frequent, and behaviorally unremarkable with a link to poor school performance. There will be a spike and wave discharge triggered through the thalamic circuitry.
- Clonic - repetitive flexion and extension of limbs or trunk
- Tonic - sustained muscular contractions
- Tonic-Clonic - sustained muscular contraction followed by repetitive flexion and extension
- Clonic-Tonic - repeptitive flexion and extension followed by sustained muscular contraction
- Tonic-Clonic-Tonic - sustained muscular contraction followed by repetitive flexion and extension followed by sustained muscular contraction
- Opisthotonic - sustained hyperposturing of back, neck, and legs, causing the back of the head to approach the heels
- Atonic - sudden loss of muscle tone
- Infantile Spasms - jerk followed by brief stiffening of the body, often occurring in series (tied to hypsarrythmia)
List the major types of focal seizures and their manifestations
- Simple partial seizures - parietal foci may trigger somatosensory experience, frontal foci may trigger focal motor output (Jacksonian March). Autonomic output can accompany focal discharge from a variety of sites (ie - unilateral sweating)
- Complex partial seizure - may arise from simple partial seizure. Foci (often limbic) generate aura or other indications of disturbed consciousness. Strong emotions (fear), facial twitching, and variable responsiveness are often seen.
What is the Jacksonian March?
Something that occasionally occurs during a simple partial seizure affecting motor output. The motor spasm begins in one area of the body and begins to work its way up to the head.
What is an “aura,” as it pertains to seizures?
An aura is a perceptual disturbance experienced by some with migraines or seizures before either the headache or seizure begins. It often manifests as the perception of a strange light, an unpleasant smell, or confusing thoughts or experiences. Most people who have auras have the same type of aura every time.
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