A stroke is basically the brain's version of a heart attack. Some even call it a "brain attack." That might sound like a bad zombie movie, but what's happening is part of your brain isn't getting enough blood, which means it isn't getting enough oxygen. The longer your brain goes without that, the more damage a stroke can do.
Why Does Oxygen Matter So Much?
Your cells use oxygen to make energy. If they don't get it, they die. It's your blood's job to deliver oxygen throughout your body.
Your brain is at the center of everything you do. Your ability to think, talk, feel, sing, and dance all goes back to your brain, and those brain cells need oxygen, too.
Your brain's a real oxygen hog. It's a small part of your body weight, but it uses 20% of your oxygen. It can't store the oxygen, so it needs a steady flow of blood to work well. Brain cells start to die if they go without oxygen for just 3-4 minutes -- and that's exactly what happens during a stroke.
With each minute that passes, you lose about 2 million brain cells. The longer you go without oxygen, the greater your chance for brain damage that can't be undone. After about 10 minutes, the damage can be severe.
How Does Oxygen Get Cut Off During a Stroke?
This can happen in different ways with the two types of stroke:
- Ischemic strokes happen when an artery that brings blood to your brain gets clogged up and blood can't flow through it. This is by far the most common type.
- Hemorrhagic strokes happen when a blood vessel in or around your brain leaks or bursts. It's also called a bleeding stroke. These are less common.
What Happens During an Ischemic Stroke?
There are two main types, and each blocks blood flow in a different way.
Embolic stroke. In this case, a clot forms in some part of your body, often your heart, and starts floating through your blood vessels. Or a piece of plaque (a buildup of cholesterol, fat, and other substances in your arteries) might break off and move along in your blood.
Eventually, the clot or chunk of plaque gets wedged in a small blood vessel in your brain. Once it's stuck, blood flow to that area stops.
Thrombotic stroke. This one's also caused by a clot in your brain. This time, a clot or blockage forms in one of the arteries that moves blood through your brain. Brain cells begin to die because blood flow is blocked.
What Happens During a Hemorrhagic Stroke?
Again, it depends on which type you have.
Intracerebral hemorrhage: With this type, a blood vessel inside your brain bursts or leaks, and that affects how much oxygen your brain gets. But there are other problems, too.
First, your skull's really hard -- it doesn't have any give to it like your stomach does. So as blood starts to build up, it puts pressure on your brain, and that can cause damage, too.
And as blood spreads through your brain, it can block nerve cells and keep them from sending messages to other parts of your body. That can affect how well you remember, speak, and move.
Subarachnoid hemorrhage: This is when a blood vessel around your brain bursts or leaks. It bleeds into the area between your brain and the tissue around it (the subarachnoid space).
Like with an intracerebral hemorrhage, brain cells are damaged by lack of oxygen and added pressure. The more blood there is, the more pressure, and the more damage.
In the days after a subarachnoid hemorrhage, you can have other issues like vasospasms, when blood vessels in your brain suddenly get narrow. That can keep blood from flowing and cause an ischemic stroke. You also might get a buildup of the fluid that normally surrounds your brain and spine, and that can add even more pressure.
Why Do Strokes Affect People in Different Ways?
A stroke only affects part of your brain, and different areas of your brain control different things. So the effects of a stroke depend on how bad it is and what part of your brain it happens in. Your symptoms may help your doctor figure out where in your brain the stroke happened.
Each side of your brain controls the opposite side of your body. So a stroke on the left side of your brain affects your right side, and vice versa.
With a stroke on the right side of your brain, you might have:
- Problems judging distances and picking things up
- Trouble reading facial expressions or tone of voice
- Weakness or paralysis on your left side
With a stroke on the left side of your brain, you might have:
- Slurred speech
- Trouble getting your words out or understanding others
- Weakness or paralysis on your right side