Back To CoursePathophysiology Textbook
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Everyone has experienced some very common everyday occurrences in life where they forgot something. We all forget where we put our car keys every now and then, and it turns out they were in the car. We can't remember where our sunglasses are when they're covering our own eyes. We even forget the names of people we hold near and dear.
If this is an every now and then occurrence, as opposed to an everyday occurrence, then it's really nothing to worry about. However, for some people affected with the disease we're going to be talking about soon, this is a serious problem.
This disease is called Alzheimer's. It is a progressive disease that affects a person's memory, attention span, learning abilities, language, and decision making, among other things. In very simple terms, Alzheimer's is the most common form of dementia. This disease usually affects people older than age 60 and the risk of someone getting affected by Alzheimer's doubles every five years after the age of 65. However, the kicker here is that while people over 60 are the ones most likely to suffer from the effects of Alzheimer's, the pathophysiological changes involved in this disease begin sometimes decades earlier.
The exact reason as to why Alzheimer's occurs is unfortunately not fully understood, as a combination of everything from genetics to environmental factors seems to play a role. The end result of all of these factors is understood at the basic level. The two hallmarks of Alzheimer's disease are plaques and tangles. Plaques are aggregates of insoluble and abnormally folded protein called beta-amyloid that surrounds neurons in the brain. Tangles are collections of threads inside of nerve cells that are made of a protein called tau.
Now, if you can recall that one is on the outside of the nerve cell and the other one is on the inside, I'll give you a trick to remember which one is where. The way I remember which is which is by thinking about the plaque that accumulates on your teeth over time. This plaque is on the outside of your teeth just like the plaque involved in Alzheimer's disease. Therefore, by default, tangles would have to be on the inside of the cells.
While we're not sure if plaques are a byproduct or cause of the disease, scientists do suspect that they may interfere with cell-to-cell communication and destroy brain cells directly as well. We also know that tangles may play a critical role in the way this disease progresses. You see, the tau proteins involved in tangles are actually really important in stabilizing certain things called microtubules inside of the nerve cells. You can think of the microtubules as the internal skeleton support structure of the cell. Not only do they support the cell, but they also serve as a road of sorts, a road that allows for the transport of chemicals and nutrients from one end of the cell to another.
Well, in Alzheimer's, the tau proteins fail to work properly, tangle up with one another, and no longer support the microtubules. The microtubular collapse causes the nerve cell to stop functioning properly. This dysfunction leads to improper communication between and within the nerve cells and eventually leads to neuronal cell death.
In essence, you can liken this entire process to the roads between cities all of a sudden collapsing and breaking apart like the microtubules did. If the roads in this country were to break apart then no one would be able to transport goods and machinery across them. If no goods or machinery can be transported, then people will end up dying, like the nerve cells, due to a lack of food, energy, and so on.
With this in mind, it is therefore no great surprise when I say that as a generality, people who have Alzheimer's have fewer nerve cells in their brain and fewer connections between their nerve cells due to all of the things I mentioned before. If you have fewer nerve cells and connections between nerve cells, then your brain cannot communicate within itself or to the body as well as before. Although no place in the brain is safe from this destruction, a particular place that is affected with all of this is called the hippocampus, and it is a structure in the brain responsible for the formation of memory.
Besides memory loss and poor memory formation, other clinical signs associated with Alzheimer's as a result of poor communication between nerve cells in your brain include:
Unfortunately, no one specific test can diagnose Alzheimer's. However, by using a combination of signs and symptoms related to Alzheimer's and by excluding other possibilities, such as vascular dementia and Creutzfeldt-Jakob disease, we can safely arrive at a diagnosis of Alzheimer's. Nevertheless, the only way to definitely diagnose Alzheimer's disease is by looking at a piece of brain tissue under the microscope after the person passes away.
Furthermore, there is no cure for Alzheimer's and no medication has been proven to slow the progression of this disease over the long term. Therefore, one of the largest classes of medication used to help improve some symptoms of Alzheimer's are called cholinesterase inhibitors. These are drugs which prevent the breakdown of a neurotransmitter called acetylcholine. The acetylcholine acts like a messenger between nerve cells. Essentially, you can equate it to the voice or language the cells use to communicate with one another.
There is another molecule, an enzyme called acetylcholinesterase, which breaks down acetylcholine. This enzyme is essentially like a signal that stops the voice or message from one nerve cell from getting through to another. Well, if we use a drug to stop this enzyme, then the message is obviously more likely to get through and the voice will be heard more clearly. Since the cells in Alzheimer's disease already have trouble communicating with one another due to the plaques and tangles that cause them to malfunction and die, this class of drugs helps to improve some of the cognitive symptoms associated with this disease by improving the way the remaining cells communicate with one another.
Again, one of the largest classes of drugs we use to try and temporarily improve the symptoms associated with Alzheimer's disease is called cholinesterase inhibitors. These are drugs which prevent the breakdown of a neurotransmitter called acetylcholine. However, they are not a cure since Alzheimer's is a progressive and incurable disease that affects a person's memory, attention span, learning abilities, language, and decision making, among other things. In very simple terms, Alzheimer's is the most common form of dementia and usually affects people older than 60.
The two hallmarks of Alzheimer's disease are plaques and tangles. Plaques are aggregates of insoluble and abnormally folded protein called beta-amyloid that surround neurons in the brain. Tangles are collections of threads inside of nerve cells that are made of a protein called tau. These hallmarks eventually end up impeding the way a cell signals within itself and between other cells, causes nerve cells to die, and decreases the amount of connections nerve cells make between one another.
Although no place in the brain is safe from this destruction, a particular place that is affected with all of this is called the hippocampus, and it is a structure in the brain responsible for the formation of memory. Unfortunately, no one specific test can diagnose Alzheimer's. However, by using a combination of signs and symptoms related to Alzheimer's and by excluding other possibilities, such as vascular dementia and Creutzfeldt-Jakob disease, we can safely arrive at a diagnosis of Alzheimer's. Some of the signs and symptoms we look for include:
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Back To CoursePathophysiology Textbook
20 chapters | 274 lessons