When does a stroke typically occur?

A stroke typically occurs when the blood supply to a part of the brain is blocked. This blockage prevents necessary oxygen and nutrients from reaching brain cells, leading to cell damage or death. There are two main types of strokes: ischemic strokes, which are caused by a blockage (such as a blood clot), and hemorrhagic strokes, which occur when a blood vessel in the brain ruptures. The definition focuses on the disruption of blood flow as the central mechanism that results in the symptoms associated with a stroke, emphasizing the importance of timely medical intervention to restore blood flow and mitigate damage.

The other options describe processes that do not align with the medical understanding of a stroke. Blood vessel expansion does not cause a stroke; in fact, that can lead to other conditions such as aneurysms. The idea of the brain receiving too much blood can relate more to conditions like hyperemia rather than a stroke and does not encapsulate the mechanism of ischemia. Moreover, nerve impulses misfiring is associated with neurological conditions such as epilepsy, not the acute vascular events that characterize a stroke. Thus, the focus on blood supply blockage is what makes this answer correct.