A neurologic disorder is caused by a dysfunction in the brain or nervous system (i.e., the spinal cord and nerves). This dysfunction can result in physical and psychological symptoms.

The brain begins developing before birth. It continues developing throughout infancy, childhood, and adolescence. Most brain cells form before birth. One type of cell is the neuron, or nerve cell. Trillions of connections exist between neurons. These do not develop until infancy.

The brain is composed of:

Gray matter. Neurons and the connections between them make up gray matter.
White matter. Long fibers called axons make up white matter. An outer layer called the myelin sheath protects them.