Brain Health Article

Common diseases and disorders

There are hundreds of diseases and disorders of the brain. There are conditions in which learning is impaired, for example, disorders of speech called aphasias and disorders in writing called dyslexia. There are disorders of thought, such as schizophrenia and Tourette syndrome. Mood disorders include depression, mania, and anxiety. There are also disorders of sleep such as insomnia and narcolepsy. The brain is subject to strokes and to cancer. The brain can also cause seizures in which neurons uncontrollably fire electrical signals. This is the hallmark of epilepsy. The basis of drug abuse and addiction is intertwined with reward pathways in the brain. There are several diseases which are involved in mental retardation, such as Fragile X syndrome and lissencephaly. There are also several diseases in which neurons degenerate or die. These diseases are collectively known as neurodegenerative diseases, and clinical symptoms depend on where in the brain the neurons are dying.

• Alzheimer's disease. Alzheimer's disease usually occurs later in life and is characterized by a decline in cognitive functions such as memory, judgment, and reasoning. The hallmark of Alzheimer's disease is deposits in the brain of a protein called amyloid beta. These deposits are found in abnormal structures called neurofibrillary tangles. Risk factors for Alzheimer's disease include mutation in genes that are responsible for production of the following proteins: amyloid precursor protein, presenilin-1, presenilin-2, and apolipoproteins. However, the role of these proteins in the development of the disease is not known.
• Huntington's disease. Huntington's disease is a genetic disease in which neurons in the brain that are involved in controlling movement die. This leads to uncontrollable, jerky, and spastic movements. There is also slowness of movement, difficulty in swallowing, and dementia. Huntington's disease occurs in the fourth or fifth decade of life and usually results in death 10 to 12 years after the first symptoms appear. The gene involved in the disease is responsible for producing a protein called huntingtin, but the role this protein plays in causing the disease is not clear.
• Parkinson's disease. Parkinson's disease is a disorder of bodily movement caused by the death of neurons that release the neurotransmitter dopamine. Symptoms include tremor, slowness of movement, rigidity, and a loss of reflexes. It is a progressive disease in which patients become unable to move. There are cases of inherited Parkinson's disease in which a gene linked to alpha-synuclein has been identified. However, the role alpha-synuclein may play in Parkinson's disease is not clear.

KEY TERMS

Axon—A fiber process of a neuron that generally conducts electrical impulses away from the cell body of the neuron.

Cell body—The part of a neuron that contains the nucleus and other cell organelles.

Dementia—Decline in mental ability.

Dendrite—A protoplasmic process of a neuron that conducts electrical impulses toward the cell body of the neuron. Usually it spreads out into many branches.

Neuron—The highly specialized cell that is the basic structural and functional unit of the nervous system.

BOOKS

Carlson, N. R. Physiology of Behavior. 6th ed. Needham Heights, MA: Allyn and Bacon, 1998.

Cohen, Barbara and Dena Wood. Structure and Function of the Human Body. 7th ed. Philadelphia: Lippincott Williams and Wilkins, 2000.

ORGANIZATIONS

Society for Neuroscience. 11 Dupont Circle, NW, Suite 500, Washington, DC 20036. (202) 462-6688. <htpp://www.sfn.org>.