The human brain is a remarkable organ. Complex chemical and electrical processes take place within our brains that let us speak, move, see, remember, feel emotions and make decisions. Inside a normal healthy brain, billions of cells called neurons
constantly communicate with one another. They receive messages from each other as
electrical charges travel down the axon to the end of the neuron. The electrical charges release chemical messengers called neurotransmitters. The transmitters move across microscopic gaps, or synapses, between neurons. They bind to receptor sites on the dendrites of the next neuron. This cellular circuitry enables communication within the brain. Healthy neurotransmission is important for the brain to function well. Alzheimer's disease disrupts this intricate interplay. By compromising the ability of neurons to communicate with one another, the disease over time destroys memory and thinking skills. Scientific research has revealed some of the brain changes that take place in Alzheimer's disease. Abnormal structures called beta amyloid plaques and neurofibrillary tangles are classic biological hallmarks of the disease. Plaques form when specific proteins in the neuron's cell membrane are processed differently. Normally, an enzyme called alpha-secretase snips amyloid precursor protein, or APP, releasing a fragment. A second enzyme, gamma-secretase,
also snips APP in another place. These released fragments are thought to benefit neurons. In Alzheimer's disease, the first cut is made most often by another enzyme, beta-secretase. That, combined with the cut made by gamma-secretase, results in the release of short fragments of APP called beta-amyloid. When these fragments clump
together, they become toxic and interfere with the function of neurons. As more fragments are added, these oligomers increase in size and become insoluable, eventually forming beta-amyloid plaques. Neurofibrillary tangles are made when a
protein called tau is modified. In normal brain cells, tau stabilizes structures critical to the cell's internal transport system. Nutrients and other cellular cargo are carried up and down the structures called microtubules to all parts of the neuron. In Alzheimer's disease, abnormal tau separates from the microtubules, causing them to fall apart. Strands of this tau combine to form tangles inside the neuron, disabling the transport system and destroying the cell. Neurons in certain brain
regions disconnect from each other and eventually die, causing memory loss. As these processes continue, the brain shrinks and loses function. We now know a great deal about changes that take place in the brain with Alzheimer's disease, but there is still much to learn. What other changes are taking place in the aging brain and its cells and what influence do other diseases, genetics, and lifestyle factors have on the risk of developing Alzheimer's disease as the brain and body age? Scientific research is helping to unravel the mystery of Alzheimer's and related brain disorders. As we learn more, researchers move ever closer to discovering ways to treat and ultimately prevent this devastating, fatal disease.