Epilepsy and seizures
How the balance between excitation and inhibition normally keeps cortical activity orderly, why a group of neurones can fire together abnormally, and how the site and spread of that discharge decide what a seizure looks like.
By the end, you can
- Describe the balance between excitatory glutamate and inhibitory GABA signalling in the cortex.
- Explain how a seizure begins as a hypersynchronous discharge and spreads.
- Distinguish focal from generalised seizures and relate focal features to the cortex involved.
- Distinguish a provoked seizure from epilepsy and list common causes of each.
- Explain why status epilepticus is an emergency.
- Recognise the classic pathology, seizure classification and tests of epilepsy, and explain how the main anti-seizure medicine classes and surgery act on the mechanism.
What it is
A seizure is a transient episode of abnormal, excessive and synchronous neuronal activity in the brain. Epilepsy is a tendency to recurrent unprovoked seizures, usually diagnosed after two unprovoked seizures more than 24 hours apart, or one with a high risk of recurrence.
3 types to tell apart
- Focal onset
- Starts in one area of one hemisphere; awareness may be kept or impaired; may spread to both sides (focal to bilateral tonic-clonic).
- Generalised onset
- Engages networks in both hemispheres from the start: tonic-clonic, absence, myoclonic and atonic seizures.
- Provoked (acute symptomatic)
- Caused by an immediate trigger such as low glucose, low sodium, alcohol withdrawal or acute brain injury; not epilepsy by itself.
Normal function
Excitation held in check
A cortical neurone receives thousands of inputs on its {{dendrites}}. Glutamate synapses depolarise it; GABA synapses from inhibitory interneurones hyperpolarise it. If the sum reaches threshold at the , voltage-gated sodium channels open and an action potential fires.
After each action potential, potassium channels and inhibitory feedback briefly silence the neurone. Interneurones also stop activity spreading too far to neighbours.
This balance lets the cortex produce precise, varied patterns of activity rather than all neurones firing together.
| Feature | Excitation | Inhibition |
|---|---|---|
| Main transmitter | Glutamate | GABA |
| Effect on membrane | Depolarises toward threshold | Hyperpolarises away from threshold |
| If increased | Seizures more likely | Seizures less likely |
| Drugs acting here | Sodium channel blockers reduce firing | GABA-enhancing drugs, e.g. benzodiazepines |
Underlying change · Step 1 of 4
Tipping the balance
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 2 of 4
A seizure starts and spreads
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 4
What the seizure looks like
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 4 of 4
Status epilepticus and other risks
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .