What is a major characteristic of ischemic stroke?

Ischemic stroke is characterized primarily by a blockage of blood supply to the brain. This occurs when a blood vessel supplying blood to the brain is obstructed, often due to a clot or narrowing of the arteries. This blockage prevents essential nutrients and oxygen from reaching the affected brain tissue, leading to cell death and subsequent neurological deficits.

The other options presented do not accurately describe ischemic stroke. Bleeding into the brain tissue refers to hemorrhagic stroke, a different condition. Gradual loss of brain function can occur in various conditions, including neurodegenerative diseases, but it is not specific to ischemic strokes, which typically present with sudden onset symptoms. Persistent headaches are more commonly associated with other medical issues, such as migraines or tension headaches, rather than specifically indicating an ischemic stroke.

Thus, the defining feature of ischemic stroke is indeed the blockage of blood supply to the brain, making option B the correct choice.