Acetylcholine - a neurotransmitter that plays an important role in learning and memory.
Amyloid precursor protein (APP) - the larger protein from which beta-amyloid is formed.
Amyloid plaques - largely insoluble deposits found in the spaces between nerve cells in the brain that are made of beta-amyloid, other molecules, and different kinds of nerve and non-nerve cells.
Apolipoprotein E - a protein that carries cholesterol in blood and that appears to play some role in brain function. The gene that produces ApoE comes in several forms, or alleles - e2, e3, and e4. The APOE e2 allele is relatively rare and may provide some protection against AD. APOE e3 is the most common allele and it appears to play a neutral role in AD. APOE e4 occurs in about 40 percent of all AD patients who develop the disease in later life; it increases the risk of developing AD.
Axon - the long, tube-like part of a neuron that transmits outgoing signals to other cells.
Beta-amyloid - a part of the APP protein found in the insoluble deposits outside neurons and that forms the core of plaques.
Brain stem - the part of the brain that connects the brain to the spinal cord and that controls automatic body functions, such as breathing, heart rate, and blood pressure.
Cerebellum - the part of the brain that is responsible for maintaining the body's balance and coordination.
Cerebral cortex - the outer layer of nerve cells surrounding the cerebral hemispheres.
Cerebral hemispheres - the largest portion of the brain, composed of billions of nerve cells in two structures connected by the corpus callosum; the cerebral hemispheres control conscious thought, language, decisionmaking, emotions, movement, and sensory functions.
Chromosome - a threadlike structure in the nucleus of a cell that contains DNA, sequences of which make up genes; most human cells contain 23 pairs of chromosomes.
Clinical trial - a research study involving humans that rigorously tests how well an intervention works.
Cognitive functions - all aspects of conscious thought and mental activity, including learning, perceiving, making decisions, and remembering.
Corpus callosum - the thick bundle of nerves that connects the two hemispheres of the cerebral hemispheres.
Dementia - a broad term referring to the symptoms associated with a decline in cognitive function to the extent that it interferes with daily life and activities.
Dendrite - the branchlike extension of neurons that receive messages from other neurons.
DNA (deoxyribonucleic acid) - a long double stranded molecule within the nucleus of the cell that forms the chromosomes and contains the genes.
Early-onset Alzheimer's disease - a rare form of AD that usually begins to affect people between ages 30 and 60; it is called familial AD (FAD) if it runs in the family.
Entorhinal cortex - an area deep within the brain where damage from AD first begins.
Enzyme - a substance that causes or speeds up a chemical reaction.
Free radical - a highly reactive oxygen molecule that combines easily with other molecules, sometimes causing damage to cells.
Gene - the biologic unit of heredity passed from parent to child; genes are segments of DNA and they contain instructions that tell a cell how to make specific proteins.
Genetic risk factor - a change in a cell's DNA that does not cause a disease but may increase the chance that a person will develop a disease.
Glial cell - a specialized cell that supports, protects, or nourishes nerve cells.
Hippocampus - a structure in the brain that plays a major role in learning and memory and is involved in converting short-term to long-term memory.
Hypothalamus - a structure in the brain under the thalamus that monitors activities such as body temperature and food intake.
Late-onset Alzheimer's disease - the most common form of AD. It occurs in people aged 65 and older.
Limbic system - a brain region that links the brain stem with the higher reasoning elements of the cerebral cortex; it controls emotions, instinctive behavior, and the sense of smell.
Magnetic resonance imaging - a diagnostic and research technique that uses magnetic fields to generate a computer image of internal structures in the body; MRIs are very clear and are particularly good for imaging the brain and soft tissues.
Metabolism - all the chemical processes that take place inside the body. In some metabolic reactions, complex molecules are broken down to release energy; in others, the cells use energy to make complex compounds out of simpler ones (like making proteins from amino acids).
Microtubules - the internal support structure for neurons that guides nutrients and molecules from the body of the cell to the end of the axon and back.
Mutation - a rare change in a cell's DNA that can cause a disease.
Nerve growth factor (NGF) - a substance that maintains the health of nerve cells. NGF also promotes the growth of axons and dendrites, the parts of the nerve cell that are essential to its ability to communicate with other nerve cells.
Neurofibrillary tangles - collections of twisted tau found in the cell bodies of neurons in AD.
Neuron - a nerve cell in the brain.
Neurotransmitter - a chemical messenger between neurons; a substance that is released by the axon on one neuron and excites or inhibits activity in a neighboring neuron.
Nucleus - the organ within a cell that contains the chromosomes and controls many of its activities.
Positron emission tomography (PET) - an imaging technique that allows researchers to observe and measure activity in different parts of the brain by monitoring blood flow and concentrations of substances such as oxygen and glucose in brain tissues.
Single photon emission computerized tomography (SPECT) - an imaging technique that allows researchers to monitor blood flow to different parts of the brain.
Synapse - the tiny gap between nerve cells across which neurotransmitters pass.
Tau - a protein that is a principal component of the paired helical filaments in neurofibrillary tangles; tau helps to maintain the structure of microtubules in normal nerve cells.
Thalamus - a small organ in the front of the cerebral hemispheres that sends sensory information to the cerebral cortex and sends other information back to the body.
Transgenic Mice - mice that have had a human gene (like APP) inserted into their chromosomes. Mice carrying the mutated human APP gene often develop plaques in their brains as they age.
Ventricle - cavity within the brain that contains cerebrospinal fluid. During AD, brain tissue shrinks and the ventricles enlarge.
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