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  • Patricia Faust

Science Alert! Science Alert! The Science of Alzheimer’s Disease and the Brain


theconversation.com


Since this is Alzheimer’s and Brain Awareness Week, I thought I would go back to the basics of how Alzheimer’s alters the brain. We first need to look of normal functioning systems of the brain. The brain contains billions of neurons. The function of the neurons is to process and transmit information by way of electrical and chemical signals. There are three basic components to neurons: Cell Body (contains the nucleus, which houses the genetic blueprint that directs and regulates the cell’s activities); Dendrites (branch-like structures that radiate from the cell body and collect information from other neurons); Axon (a cable-like structure that extends from the other end of the cell body and transmits messages to other neurons).


The function and survival of neurons depend on these key biological processes:


· Communication: When a neuron receives a signal from other neurons, it generates an electrical charge that travels down the length of the neuron’s axon to a specialized structure called the synapse, where the axon comes in close contact with the dendrites of another neuron. There, each neurotransmitter molecule binds to a specific receptor molecule, like a key fitting into a lock, and triggers chemical or electrical signals within the dendrite that either stimulates or inhibits the next neuron’s activity. Each neuron’s axon can make connections with the dendrites of many other neurons, and each dendrite can receive connections from many axons. In fact, scientists estimate that in this brain cell communications network, one neuron may have as many as 7,000 synaptic connections with other neurons.


· Metabolism: This term encompasses all chemical reactions that take place in a cell to support its survival and function. These reactions require chemical energy in the form of glucose and oxygen, which is supplied by blood circulating through the brain. The brain has one of the richest blood supplies of any organ and consumes up to 20 percent of the energy used by the human body – more than any other organ.


· Repair, remodeling, and regeneration: Unlike many cells in the body, which are relatively short-lived, neurons have evolved to live a long time – more than 100 years in humans. As a result, neurons must constantly maintain and repair themselves. Neurons continuously remodel their synaptic connections depending how much stimulation they receive from other neurons. Neurons may strengthen or weaken synaptic connections, or even break down connections with one group of neurons and reestablish connections with a different group of neurons. In addition, a number of brain regions continue to generate new neurons, even in adults. Remodeling of synaptic connections and the generation of new neurons are thought to be important for learning, memory, and possible brain repair.


Neurons are the cells responsible for transmitting messages between different parts of the brain, and from the brain to the muscles and organs of the body. However, the brain contains other cell types as well. In fact, glial cells are by far the most numerous cells in the brain, outnumbering neurons by at least 10 to 1. Glial cells (of which there are several varieties) surround neurons and play critical roles in supporting neuronal function. For example, glial cells help protect neurons from physical damage and are responsible for cleaning foreign substances and cellular debris from the brain. To carry out these functions, glial cells often act in collaboration with blood vessel cells, which in the brain have specialized features not found in blood vessels elsewhere in the body. Together, glial and blood vessel cells regulate the delicate chemical balance within the brain to ensure optimal neuronal function. (www.nia.nih.gov)


How Does Alzheimer’s Disease Affect the Brain?


Through the process of aging, the brain may shrink to some degree. I Alzheimer’s disease damage is widespread as many neurons stop functioning, lose connections with other neurons, and die. Alzheimer’s disrupts processes vital to neurons and their networks, including communication, metabolism, and repair.

At first, the disease typically destroys neurons and their connections in parts of the brain involved in memory, including the entorhinal cortex and the hippocampus (center of learning and memory). It later affects areas in the cerebral cortex responsible for language, reasoning, and social behavior. Eventually, many other areas of the brain are damaged, and a person with Alzheimer’s becomes helpless and unresponsive to the outside world.


What Are the Main Changes in the Brain of a Person with Alzheimer’s?

The three abnormalities most evident in the brains of people who died with Alzheimer’s are:


· Amyloid Plaques: Found in the spaces between neurons, plaques consist predominantly of abnormal deposits of a protein fragment called beta-amyloid. Beta amyloid comes in several different molecular forms. One of these, beta-amyloid 42, has a strong tendency to clump together. When produced in excess, beta-amyloid 42 accumulates into plaques. Scientists have not yet determined if plaques are a cause or a byproduct of Alzheimer’s disease.


· Neurofibrillary tangles: Found inside neurons, neurofibrillary tangles are abnormal clumps of a protein called tau. Healthy neurons are internally supported in part by structures called microtubules, which help guide nutrients and molecules from the cell body to the axon and dendrites. Researchers believe that tau normally binds to and stabilizes microtubules. In Alzheimer’s, however, tau undergoes abnormal chemical changes that cause it to detach from microtubules and stick to other tau molecules, forming threads that eventually clump together to form tangles. The tangles disrupt the microtubule network and create blocks in the neuron’s transport system. Abnormal tau may also cause blocks in synaptic signaling.


· Loss of neuronal connections and cell death: In Alzheimer’s disease, the synaptic connections between certain groups of neurons stop functioning and begin to degenerate. This degeneration may be due to the abnormal deposits of beta-amyloid and tau. When neurons lose their connections, they cannot function properly and eventually die. As neuronal injury and death spread through the brain, connections between networks of neurons break down, and affected regions begin to shrink in a process called brain atrophy. By the final stage of Alzheimer’s, damage is widespread, and the brain tissue has shrunk significantly.

Amyloid plaques, neurofibrillary tangles, synaptic loss, and cell death are the most striking features of the Alzheimer’s brain. However, scientists are now realizing that many other cellular changes occur in the brain during the Alzheimer’s disease process. For example, glial cells show abnormalities, as certain populations of glial cells begin to swell up and divide and produce more glial cells.


The Alzheimer’s brain also shows signs of inflammation, a tissue response to cellular injury. In addition, brain blood vessel cells as well as brain neurons show signs of degeneration. Some could be a result of neuronal malfunction, while others could contribute to neuronal malfunction. (www.nia.nih.gov)


After this explanation of what happens to the brain with Alzheimer’s, I hope you can understand how difficult it is to come up with treatment protocols and cures. Alzheimer’s is epidemic and one of the best ways to delay or even prevent getting this disease is to live a brain healthy lifestyle. Get exercise, challenge your brain, eat nutritious food, connect with other people, get good sleep and reduce your stress. Take these preemptive measures and make your brain a priority in your self-care. Having a high functioning brain until the end of your days is quite a reward for living healthy.


Reference:

National Institute on Aging/National Institute on Health. A Primer on Alzheimer’s Disease and the Brain. Retrieved from www.nia.nih.gov/alzheimers/publication/2013-2014-alzheimers-disease-progress-report/primer-alzheimers-disease-and-brain


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