DEAR DOCTOR K: What are the warning signs of stroke? Why is it important to be able to recognize them?

DEAR READER: Nothing makes me sadder than to see someone suffer a stroke that could have been avoided. Not all strokes can be avoided, but many produce warning symptoms that can trigger preventive actions — if they are recognized.

Your brain relies on a steady supply of oxygen-rich blood to do everything. When the blood supply to any part of your brain is suddenly interrupted, it can have serious effects. You may lose strength, have trouble coordinating your movements, and have trouble speaking or understanding what people are saying to you. You may not be able to think clearly or remember things. You may have trouble seeing or hearing.

A stroke occurs when an injury to a blood vessel deprives a part of the brain of its constant blood supply. As a result, brain cells can die, taking with them the ability to move, speak, feel or think.

If the brain's blood supply is quickly restored, a person may recover from a stroke with little or no disability. That's why it is vital to recognize the warning signs of stroke in yourself and in others — and to get to an emergency room immediately if they occur.

If you experience any of these symptoms, immediately dial 911: