Just a quick preface: I am NOT a licensed physician. I am a high school student who enjoys researching interesting medical phenomena. These posts are just a summary of my research and the answers to questions I had while conducting it!!
Multiple Sclerosis or MS is a rare autoimmune and neurodegenerative disease. In order to get hints about what is specifically affected by MS, we first must look at the name itself. Sclerosis in medicine means scarring. So you may ask yourself, what is affected or scarred by MS? MS targets nerve cells in particular. Unlike in Langerhan’s Cell Histiocytosis, a disease we have talked about before, the autoimmune response in MS is triggered not by the overproduction of histiocytes, but by the misidentification of the myelin lining that protects the axon or nerve fibers. This elicits an immune response and results in the histiocytes or T-cells to strip the myelin coating of the nerve cell, thus exposing the axon. In order to understand the significance of this, we must fully understand all the parts and functions of the nerve cell and how the nervous system works. The nerve cell essentially consists of three main parts the soma, axon, and the synapses. So what is housed in the soma? The soma houses the nucleus and is surrounded by dendrites which are tree-like extensions that protrude off of the soma. The responsibility of the dendrites is to catch or receive electrical signals that are used to elicit a certain action or function,
the dendrites conduct this electrical signal to the nucleus which is responsible for interpreting the data and producing a new signal. So what is in the axon portion? The axon portion contains the axon or nerve fibers which are responsible for conducting the new electrical signal to the synapses. The axon is housed in a myelin coating which acts as an insulator for the signal and creates specific points along the axon called the nodes of Ranvier which are sites for ion pathways that help to strengthen and increase the signal velocity and density. So what are synapses? Synapses are essentially the broadcasters of these signals to other nerve cells where the signal is received by the dendrites attached to the new cell. Now that we have a good understanding of the functions a nerve cell carries out, we can further analyze how an MS patient’s nerve cells are affected. The key here is the stripping of the myelin coating that not only protects the axon but also creates the nodes of Ranvier. With the removal of that vital coating by histiocytes, the method of conduction in the nerve cell completely shifts from saltatory conduction to continuous conduction. Understanding the difference between these two methods is paramount in your understanding of MS. Saltatory conduction is the default method of conduction in the nerve cells and uses the concentrated amount of ion pathways in the nodes of Ranvier where many ions are released quickly causing a faster depolarization and action potential. With a faster depolarization and action potential, a signal can be carried much faster. Essentially, the nodes of Ranvier act as a signal amplifier which allows the signal to maintain current density as it travels throughout the body. The myelin lining also acts as an insulator for the signal ensuring that the signal strength is not lost or interfered with. The result is a clear, fast, and uninterrupted signal that can be sent throughout the body at lightning speeds. The problem is that patients with MS have a stripped myelin covering on their nerves meaning that they cant rely on Saltatory conduction as there are no nodes of
Ranvier present on the axon. As a result, these exposed nerve cells rely on the use of continuous conduction. This is a less efficient and slower method that often results in slower and distorted signals. Without the nodes of Ranvier to act as a signal booster or the myelin coating
ensuring consistent signal density, the number of ion pathways that are needed to carry the signal continuously increases drastically as depolarization and action potentials become harder to achieve. The problem here is that the number of ion pathways is relatively constant meaning that in continuous conduction there is a decrease in signal density as the signal is carried and a decrease in speed of the signal. This causes incorrect or even no signaling at all. To make things worse, after the myelin lining has been stripped from the axon the ‘sclerosis’ potion of the condition begins to set in as the body sees the damage to the myelin lining as damage which requires the recruitment of excess collagen to form dense scar tissue on the axon which serves to inhibit the signals even more and can even stop signals altogether. It is this reason why MS is neurodegenerative, although technically part of the brain doesn’t die, it becomes ineffective as it cant send or receive any signals. So what are the symptoms or physical
manifestations of MS? The symptoms of MS include numbness or weakness in one or more limbs, electric-shock sensations, tremor, partial or complete loss of vision, slurred speech, fatigue, and dizziness. The disease course for MS can vary, most people with MS experience a relapsing-remitting disease course or they have periods in which new systems develop and then periods of relapse in which the new symptoms improve partially or completely. These relapses are followed by remission that can last multiple months. Specifically, there are two types of progression in people with MS, Primary-progressive MS, and Secondary-progressive MS. The difference between the two is that patients with Primary-progressive MS experience a slow onset and progression without relapses, while patients with Secondary-progressive MS experience a steady progression with or without relapses in a period of 10 to 20 years after the onset of symptoms. So how is MS diagnosed? There are many ways in which MS can be diagnosed: blood tests, spinal taps, MRI, and Evoked potential tests. Essentially, all the methods help to identify specific antibodies or markers that are specific to MS. At the moment there is no cure for MS, but there are treatments that can decrease the speed of relapses and help to decrease the severity of symptoms. Corticosteroids can be used to decrease nerve inflammation which promotes the development of scar tissue. Ocrelizumab is the only FDA approved disease-modifying therapy (DMT) for use on patients with primary-progressive MS. But for people with relapsing-remitting MS there are many DMT’s available including interferon beta medications which are used to reduce the frequency and severity of relapses. Glatiramer acetate is a medication that can block the immune system’s attack on myelin. The prognosis for MS is considered to be 25-35 years after the diagnosis. Some of the most common causes of death in patients with MS are not from MS directly but rather from complications. These include immobility, chronic urinary tract infections, and compromised swallowing and breathing.
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