Final answer:
In strokes, head traumas, and spinal cord injuries, cell destruction occurs in two phases: the immediate initial damage and the secondary injury caused by excitotoxicity. These conditions lead to irreversible cell death and can result in permanent functional deficits.
Step-by-step explanation:
The two phases of cell destruction common to strokes, head traumas, and spinal cord injuries are the acute initial damage from the insult, and the secondary injury caused by excitotoxicity. The initial damage occurs due to the immediate physical harm or lack of blood flow during the incident. The secondary injury, which may occur hours to days after the initial event, involves a harmful biochemical cascade including excitotoxicity—in which an excess of glutamate causes an overactivation of receptors, leading to calcium influx into neurons and resulting in cell death or necrosis.
Stroke is an example of such an injury, where the loss of blood flow to a part of the brain, or a hemorrhagic event where an artery bursts, leads to an area of dead tissue known as the ischemic core. The brain cells in the ischemic penumbra surrounding the core are at risk but can potentially be saved with prompt medical intervention. Traumatic brain injury (TBI) and spinal cord injuries also follow a similar pattern of primary and secondary destruction, and just like stroke, they are major medical emergencies that can lead to permanent damage or disabilities if not adequately treated.