We all know that Alzheimer's has a deep impact on the brain, but do we know exactly how? Here's an in-depth look.
The brain's structure is made up of billions of neurons that connect to each other. These connections have stored the memories and abilities we gain during our lifetime. Every day, countless electrical impulses, called synapses, are transmitted through these connections, which make up basically every interaction we have with the world. With synapses, there are also various chemical substances, called neurotransmitters, involved, which help to facilitate the transmission of the electrical signal and can impact our current mood, as well as other vital processes.
Each brain cell is comprised of several parts, including the body, which contains the nucleus as well as all the necessary data that regulates and directs its activities. The dendrites are another part of the cell, which consists of small, branch-like structures that connect to the dendrites of other cells to recieve information is received. The axon, the final part of the neuron is a tail-like structure, which also has dendrites on the tip and transmits the information from the cell to other neurons.
In order to stay alive and keep healthy, the neurons are dependent on several key biological processes. The connection between each neuron is the first of these processes. When a neuron establishes a connection with another one, an electrical charge travels down the length of its axon until it reaches the dendrite. This electrical impulse causes the dendrites to release neurotransmitters in the synapse — the gap between the neurons. These chemicals travel onto the other neuron and bind themselves onto their receptors, which can either stimulate or inhibit its activity. This transaction between neurons is theorized to happen on a network of neurons, where a single neuron could be connected with up to 7,000 other brain cells.
The second process is inherent to each and every cell of the body — the metabolism of chemicals and nutrients necessary for the cell to survive. Like any other cell, neurons require glucose and oxygen in order to perform its metabolic process and obtain the energy it needs to survive and function properly. Of all the bodily structures, the brain is the one that has one of the amplest blood supplies and can require up to 20 percent of the total energy generated by the human body to maintain its functions.
Lastly, the final process involves the repair, remodeling, and regeneration of the brain cell. Unlike other cells, neurons have evolved to live for very long amounts of time. They are constantly repairing and remodeling the structure of their synaptic connections to optimize the information it is receiving from the person’s experiences. Sometimes, the brain can also break certain synaptic connections in order to accommodate others. When reaching maturity, the adult brain is also capable of creating entirely new brain cells, in a process called neurogenesis. This process is paramount for aiding, learning, memory, and even repairing.
The brain is connected to each and every part of our body through the spinal cord. From this hub of information, the nerve endings extend towards our muscles and other structures. The brain sends and receives signals at nearly every time in our lives; even when we sleep. However, there are certain diseases that can disrupt the flow of information, and even destroy the neural connections already present in our brain. Alzheimer’s is just one disease that can progressively destroy the neurons of the brain, causing a wide variety of neurological and psychological symptoms. This neurodegenerative disease worsens through time and causes loss of function and cell death, among other symptoms.
It is not unheard of for the brain to reduce in size as the person matures. In fact, it is known that the brain loses some of its mass as the person grows older. However, despite the fact that the brain shrinks a little in size, the neural connections remain intact. Alzheimer’s disease directly affects these connections and causes widespread damage to every structure in the brain. With this disease, neurons will lose connections, stop functioning, and eventually die. The disease is known to disrupt all three vital processes that keep the neurons healthy and functioning.
In the beginning, Alzheimer’s typically targets and destroys the areas responsible for memory, which includes the entorhinal cortex and the hippocampus. In the following stages, Alzheimer’s targets other structures associated with language, behavior, and reasoning. Finally, the disease attacks and destroys areas that oversee and regulate the vital bodily functions. Ultimately, the disease becomes fatal, and the person dies around 5 to 8 years after receiving their diagnosis.
Alzheimer’s attacks the brain in a few ways.
The most notable evidence of Alzheimer’s is seen when examining the posthumous brain of a patient. At a glance, it is possible to discover a buildup of plaque-like structures called amyloid plaques in several areas of the brain, which seem to replace the areas that were affected by the disease. The plaque is caused by a buildup of a substance derived from the breakdown of a protein called the amyloid precursor protein. This buildup gathers between the neurons, interrupting their function, and cutting off their connections. One form of the plaque formations, in particular, the beta-amyloid 42, is especially toxic to the brain and is the most common substance from which said plaque is created.
Alzheimer’s also attacks from within the cell, through structures called neurofibrillary tangles. In a healthy person, their neurons are supported and their axons kept strong by structures called microtubules. There is a certain structure called tau, which is supposed to bind to the microtubules to keep them stable. In a person with Alzheimer’s, tau detaches from the microtubules and tangles within the cell, causing internal blockages that slowly kill the structure by impeding the transfer of nutrients and dumping waste material from the neuron’s metabolic process.
Debris and waste buildup is also an issue present in the brain of an Alzheimer’s patient. In a regular person, there is a buildup of glial cells, which engulf and travel throughout the brain, clearing it of debris and other substances. This process is achieved through the actions of a type of glial cell, called microglia. In a person with Alzheimer’s, the microglia fails to properly clear the brain of debris and toxins, which leads to inflammation, and a decrease in brain function.
There is still much that we don’t know about Alzheimer’s disease. Every day, researchers are hard at work in hopes of understanding the mechanisms that drive the onset and progress of the disease. What’s very clear is that the only things that remain are the breaking of neural connections, the death of brain cells, and brain atrophy, which usually results in the person’s death.