Brain

The brain is a pinkish-grey, wrinkled organ that fills the skull — looking, for all the world, like a huge walnut. It is hard to believe, from its appearance, that this ugly lump of jelly contains the mechanisms of thought, perception, will, and consciousness, that it is the seat of our personality. Its 100,000 million nerve cells, each with an average of 100,00 connections from other neurons, makes the human brain the most complicated and least understood object in the known universe. The vertebrate brain is the large anterior portion of the central nervous system . The "cranial vault" of the skull encases the brain in most vertebrates. In invertebrates, the enlarged and specialized anterior ganglion of the central nervous system is often referred to as a brain, although not all scientists regard it as a true brain.

stroke

A stroke is a condition in which the brain cells suddenly die because of a lack of oxygen. This can be caused by an obstruction in the blood flow, or the rupture of an artery that feeds the brain. The patient may suddenly lose the ability to speak, there may be memory problems, or one side of the body can become paralyzed.
The two main types of stroke include ischemic stroke and hemorrhagic stroke.