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.

Intellectual disability

Intellectual disability is a term used when a person has certain limitations in mental functioning and in skills such as communicating, taking care of him or herself, and social skills. These limitations will cause a child to learn and develop more slowly than a typical child.
Children with intellectual disabilities (sometimes called cognitive disabilities or mental retardation) may take longer to learn to speak, walk, and take care of their personal needs such as dressing or eating. They are likely to have trouble learning in school. They will learn, but it will take them longer. There may be some things they cannot learn.