What is a stroke? (brain basics + types)
A stroke is a brain emergency: blood flow to part of the brain is suddenly cut off or a vessel bursts, and brain cells begin to die within minutes. This lesson explains what a stroke is, the main types, and why every minute counts
Why this matters
Knowing what a stroke is — and that a clot and a bleed are treated in opposite ways — is the foundation for every decision that follows, from calling for help to understanding hospital treatment
What the brain needs to work
Your brain is only about 2% of your body weight, but it uses roughly 20% of the oxygen and sugar (glucose) your blood carries. It has almost no way to store fuel of its own, so it depends on a steady, second-by-second blood supply. When that supply stops, the affected brain cells can begin to die within minutes
This is why clinicians say “time is brain.” Each part of the brain controls something specific — moving an arm, forming words, swallowing — so the symptoms a person has point to exactly which area has lost its blood flow
For example: Think of the brain like a city that runs entirely on electricity with no backup generators. The moment a power line is cut, the neighborhood it served goes dark almost immediately — and the longer the power is out, the harder it is to bring that neighborhood fully back
Ischemic stroke — a blockage
About 87% of strokes are ischemic, meaning a clot or fatty buildup blocks an artery and stops blood from reaching part of the brain. The clot may form in the brain’s own vessels or travel there from the heart or neck
Because the blockage is physical, emergency treatment focuses on reopening the vessel fast — with clot-busting medication and, for larger clots, a procedure to physically remove it. Both work best within hours, which is why getting to hospital quickly matters so much
For example: A common pattern: someone with an irregular heartbeat (atrial fibrillation) forms a small clot in the heart, it travels up to the brain, and they suddenly can’t lift one arm
Hemorrhagic stroke — a bleed
The other roughly 13% of strokes are hemorrhagic: a weakened blood vessel leaks or bursts, and blood spills into or around the brain. The escaping blood both starves the area downstream and creates pressure that damages nearby tissue
High blood pressure is the biggest cause. Treatment is very different from an ischemic stroke — the priority is to control the bleeding and pressure — which is one reason a brain scan is always done before any clot-busting drug is given
For example: Years of untreated high blood pressure can wear out a small vessel deep in the brain until it finally gives way, often causing a sudden, severe headache unlike any before
TIA — the warning stroke
A transient ischemic attack (TIA), or “mini-stroke,” causes the same symptoms but they go away — usually within minutes — because the blockage clears on its own. It is not harmless. A TIA is a loud warning that a full stroke may be coming, sometimes within days
The right response to a TIA is identical to a stroke: call emergency services immediately, even if the person already feels fine
Watch and connect
Understanding the Different Types of Stroke (3D animation) - A short animation showing how ischemic and hemorrhagic strokes damage the brain — watch how blood flow is lost.
In practice
At dinner, your father’s face droops on one side and his speech slurs, but two minutes later he seems completely normal and insists he’s fine. What do you do? Call emergency services anyway. Symptoms that come and go are a TIA — a warning that a major stroke could follow soon — and only a hospital can find out why and prevent the next one
★ Key takeaways
- A stroke is a brain emergency caused by a blocked vessel (ischemic, ~87%) or a bleed (hemorrhagic, ~13%)
- Brain cells die quickly without blood — “time is brain.”
- A brain scan comes first because clots and bleeds are treated in opposite ways
- Even symptoms that disappear (a TIA) are an emergency — call for help
Lesson quiz
Check this lesson
Answer these lesson-specific questions before continuing. They focus on the decisions, scenarios, and safety points covered above.
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Complete every question, then submit once to see all correct and incorrect answers.
References
- Tier 1American Stroke Association2024About Stroke
- Tier 1American Stroke Association2024Types of Stroke
- Tier 1Centers for Disease Control and Prevention2024Stroke Facts