A stroke has the same relationship to the brain as a heart attack does to the heart. Both result from a blockage in a blood vessel that interrupts the supply of oxygen to cells, resulting in the death of vital tissue. The consequences of a stroke, the type of functions affected, and the severity, depend on where in the brain the blockage has occurred and the extent of the damage. Other processes in the brain compound the damage. Researchers are working to discover the cycle of events involved in brain cell death after oxygen is lost.
Calcium reacts within the neurons to release harmful substances that damage cells.
Natural particles released by the body's chemical processes called oxygen-free radicals may also play a role in the cell damage caused by a stroke. Confronted with substantial injury, however, PARP over-responds and takes up a substance called ATP, the major source of energy in cells. The cells die. Within minutes of a stroke, the zone of initial cell death is surrounded by additional damaged and dying brain cells. This process can continue for hours.