Some people compare the brain to a computer. I feel that this is not an accurate comparison because the brain is more complex than the entire Internet!
About the Brain
Even though the brain is really one organ, it controls much more.
The brain contains cerebrospinal fluid which is housed in ventricles.
In diseases these ventricles are sometimes enlarged. In schizophrenia and in Alzheimer's disease, this enlargfement is due to tissue loss.
Many books have been written on the complexity of the brain.
Diseasis
Pathology has been seen in the brain in many diseases including Parkinson's disease, Huntington's chorea, Alzheimer's disease, schizophrenia, mental retardation, etc. In multiple sclerosis demylination is seen. Amyotrophic lateral sclerosis is also called Lou Gherig's disease.
Conclusions
Much more research is needed. The brain has been studied on a cellular level.
The brain is a neuron jungle, but glia are also very important.
This is very controversial, but mental diseases are brain diseases. The brain is made from, repaired by, and fueled by the food that we eat. To ignore this is a mistake.