My serious enemy is brain injury. Despite my watery cushion and fortress skull, I can still be slammed around by blows, accidents, falls. I respond in many different ways. I may swell, just as a mashed finger does. But because I am confined in a bony prison, I have no room to swell. Pressure develops. Symptoms range from blackouts to death.

Stroke is major problem. A clot forms in one of my small blood vessels or one of my small arteries weakens and bursts, and part of me starves. Symptoms range from minor mental lapses to total paralysis and death. Little can be done to correct the effects of stroke in some cases.

In others, rehabilitation is possible. Its success will depend on which part and how much of me has been destroyed.