Seizures and EEG Flashcards
In general terms.
What is a neurone?
Neurones (AKA nerve cells) are the functional units of the nervous system; they can generate and carry electrical impulses.
What are glial cells?
Essential components of nervous system function that work mostly to support neurones.
What two anatomical components make up the CNS?
Brain and spinal cord.
What makes up the PNS?
Neurones and parts of neurones outside the CNS.
What is the term for clusters of the cell bodies of neurones found outside the CNS?
Ganglia (ganglion, singular)
Note: not a trick question.
What is the term for the axons of peripheral neurons that travel a common route and are bundled together?
Nerves.
Name the three classes of neurones.
- Sensory neurones
- Motor neurones
- Interneurones
What is the role of sensory neurones?
To obtain information of what occurs inside and around the body and carry that info to the CNS for processing.
What is the role of motor neurones?
To retrieve information from other neurones and convey commands to muscles, organs, and glands.
Interneurones are only found in which system, CNS or PNS?
CNS
What is the function of interneurones?
To connect one neurone to another; they receive information from either sensory neurones or interneurones and transmit information to either motor neurones or other interneurones.
Which of the three classes of neurone are the most numerous?
Interneurones
What are the basic functions of a neurone?
- To receive signals
- Integrate incoming signals (determine whether it should be passed along)
- Communicate signals to target cells
Name the three anatomical sections of a neurone.
- Soma (cell body)
- Dendrites
- Axon
Incoming nerve signals can be either ____ or ____ in nature.
Excitatory (tending to make the neurone fire) or inhibitory (tending to prevent the neurone firing)
Describe the basic function of neurotransmitters.
An action potential triggers the release of the neurotransmitter from the presynaptic cell. The neurotransmitter molecules cross the synapse to bind to membrane receptors on the postsynaptic cell, conveying an excitatory or inhibitory signal.
Purkinje cells are found in which region of the brain?
Cerebellum
What is particular about Purkinje cells?
They have a complex dendritic tree which allows them to receive and integrate a large number of synaptic inputs
Name the four main types of glial cells
- Astrocytes (CNS)
- Oligodendrocytes (CNS)
- Microglia (CNS)
- Schwann cells (PNS)
What is the role of astrocytes?
- Regulate cerebral blood flow
- Maintain CSF composition
- Regulate communication between neurones at the synapse
- Contribute to blood-brain barrier formation during development
What is the role of microglia?
Microglia are related to macrophages, acting as scavengers to remove dead cells and other debris.
What are the roles of oligodendrocytes (CNS) and Schwann cells (PNS)?
Production of myelin, the substance that sheaths axons and increases the speed at which APs travel along them
What is the meaning of ‘afferent’?
Ascending; towards the brain
What is the meaning of ‘efferent’?
Descending; away from the brain
Describe regeneration capability with regards to the CNS and PNS
The CNS is capable of very little regeneration, whereas the PNS is able to regenerate unless significantly compromised.
What are the two main components of grey matter?
Cell bodies and synapses
Note: one-word answer
What occurs in grey matter at the neurone level?
Integration
What is the main component of white matter?
Myelinated axons
Name six common CNS NTs
- Acetylcholine (+)
- Dopamine (+)
- GABA (-)
- Noradrenaline (+)
- Glutamate (+)
- Serotonin (+)
Name four common PNS NTs
- Acetylcholine (+)
- Noradrenaline (+)
- Adrenaline (+)
- Glycine (-)
What does EEG stand for?
Electroencelography
What brain waves are expected when a person is alert/working?
Beta
What is the frequency of beta brain waves?
14 - 20 waves per second
What brain waves are expected when a person is relaxed/reflecting?
Alpha
What is the frequency of alpha brain waves?
8 - 13 waves per second
What brain waves are expected when a person is drowsy/meditating?
Theta
What is the frequency of theta brain waves?
4 - 7 waves per second
What brain waves are expected when a person is asleep/dreaming?
Delta
What is the frequency of delta brain waves when a person is asleep/dreaming?
3 - 4 waves per second
What brain waves are expected when a person is in deep and dreamless sleep?
Delta
What is the frequency of delta brain waves when a person is in deep and dreamless sleep?
0.5 - 2 waves per second
What are gamma brain waves?
Fast brain waves with high frequency (>30/s)
Note: researchers are unsure of their function but theorise that they see ‘whole pictures’ and put together pieces of information. Some types of meditation have very active gamma waves, the waves disappear under general anaesthesia, and they are reported to be absent in people with schizophrenia (contentious).
Describe the progression of brain waves as a person falls asleep.
Note: ‘Awake’ to stage 4 occur within an hour.
Awake: beta
Stage 1 (drowsy): alpha
Stage 2 (light sleep): theta
Stage 3 (moderate sleep): beginning delta
Stage 4 (deep sleep): delta
Stage 5 (REM sleep): like beta/alpha/theta but in different brain region
What is a seizure from an EEG perspective?
Abnormal oscillatory activity in the nervous system; abnormal brain waves.
Note: for the purposes of this unit.
What is the dx criteria for epilepsy?
At least two independent seizures confirmed by EEG activity
List some causes of seizure other than epilepsy.
- Meningitis/encephalitis
- Severe hypotension
- Electrolyte disturbance
- Hyperthermia/febrile convulsions
- Drugs
- CNS pathology (e.g. stroke/tumour/haemorrhage)
List some seizure triggers for people with epilepsy
- Stress
- Lack of sleep
- Infections
- Drugs (or lack of)
- Bright light (photosensitive epilepsy)
- Extremes of temperature
- Dehydration
Epilepsy can be due to ____ ____.
Genetic defect
List three possible causes of epilepsy
- Genetic defect (usually subtle)
- Altered neuronal excitability
- Ion channel problems (too many/active Na channels, or too few/inactive K channels)
Focal/partial seizures involve ____ hemisphere/s of the brain.
One hemisphere
Generalised seizures involve ____ hemisphere/s of the brain.
Both hemispheres
Name two common types of generalised seizures
Tonic clonic (grand mal)
Absence (petit mal)
What does ‘tonic’ mean in terms of tonic clonic seizures?
Muscle contraction
What does ‘clonic’ mean in terms of tonic clonic seizures?
Convulsions
Describe the tonic phase of tonic clonic seizures
- Pt loses consciousness/falls
- All skeletal muscles tense
- May make sound as air leaves lungs
- Lasts a few seconds
Describe the clonic phase of tonic clonic seizures
- Convulsions (caused by rapid contraction and relaxation of muscles)
- Violent shakes/twitching
- Eyes roll back
- Pt may bite tongue
- Cyanosis as respiratory muscles contract (in some cases)
List some features of absence seizures
- Sudden interruption of consciousness/awareness
- Sudden ‘blank stare’
- Pt stops moving/talking
- Typically short (few seconds/minutes)
- Pt usually has no memory of event
What type of EEG morphology is typical of absence seizures?
Spike and wave morphology (sometimes called sawtooth morphology)
Name four types of generalised seizures (not including tonic-clonic or absence)
- Myoclonic
- Clonic
- Tonic
- Atonic
Describe a myoclonic seizure
Brief but significant muscle spasms; may be localised to a smaller area
Describe a clonic seizure
Constant convulsions without stiffening, sometimes with cyanosis. Can be difficult to distinguish between clonic and tonic-clonic.
Describe a tonic seizure
Often called ‘drop attack’; constant muscle contractions, sometimes cyanosis.
Describe an atonic seizure
Sudden loss of consciousness or muscle tone; also called a ‘drop attack’, though is the opposite of a tonic seizure.
True/false: most seizures start focal but rapidly progress to generalised.
Note: this terminology is no longer officially used but is still common in medical settings
What is the difference between ‘simple partial’ and ‘complex partial’ seizures?
Simple partial: consciousness not altered
Complex partial: impaired consciousness
Benign juvenile epilepsy (AKA benign Rolandic epilepsy) starts between what years of age?
3 - 13
Benign juvenile epilepsy usually peaks at what age?
8
When does benign juvenile epilepsy usually resolve?
Late adolescence
Benign juvenile epilepsy is usually genetic, with a susceptibility region on which chromosome?
Chromosome 15
Benign juvenile epilepsy affects regions near which receptor?
Acetylcholine receptor
Benign juvenile epilepsy is an “impairment of brain ____”
Maturation
Benign juvenile epilepsy seizures usually start in which area of the brain?
Central sulcus
What features in a classic EEG of benign juvenile epilepsy?
Centrotemporal spikes
Cells of an epileptic focus have characteristics that contribute to their ____.
Hyper-excitability
The membrane potential of cells with an epileptic focus is often significantly (higher/lower), making them closer to threshold and thus easier to activate.
Lower (less negative)
Once action potential is triggered in cells with an epileptic focus they can enter a repetitive loop similar to what other electrical phenomenon?
Re-entrant tachycardia
What characteristic of cells with an epileptic focus account for the post-ictal period?
Post-seizure cells remain further from threshold and much less sensitive to ion levels, lasting minutes/hours.
Are GABA-minergic neurones inhibitory or excitatory?
Inhibitory
Are glutaminergic neurones inhibitory or excitatory?
Excitatory
Which are more sensitive to seizure-mediated cell death, GABA-minergic or glutaminergic neurones?
GABA-minergic
Which neurones are more resistant to seizure-mediated cell death and will extend to areas vacated by GABA neurones, reducing GABA inhibitory effects and so possibly increasing seizure frequency and intensity?
Glutaminergic neurones
Midazolam is a short acting ____.
Benzodiazepine
Midazolam is a CNS depressent which (increases/decreases) GABA inhibition.
Increases
List some long-term goals of epilepsy rx
- Limit neuronal excitability
- Stabilise inactive state of Na channels
- Potentiate GABA activity
What is the core long-term goal of epilepsy rx?
To limit overactivity without too many side effects on normal neural activity
What is computed tomography (CT/CAT scan)?
A series of x-rays that are digitally reconstructed into a three-dimensional (tomographic) image
List some characteristics of computed tomography use
- No superimposition of images of structures outside the area of interest
- High-contrast resolution
- Area of interest can be studied from many angles
- Cheaper and more accessible than MRI but not as accurate
Describe the magnetic resonance imaging (MRI) process.
- Strong magnets excite hydrogen nuclei in water molecules in the body
- Protons start to spin in a different direction (resonance), producing a different signal depending on tissue density and water content
- Three-dimensional image ‘slices’ are produced
