By Melina Fatemi
Every five minutes, someone is diagnosed with multiple sclerosis, a disease affecting over 2.8 million people worldwide. But what is multiple sclerosis, exactly? Multiple sclerosis, also referred to as MS, is a demyelinating disease. To understand what this word means, it is helpful to look at a neuron diagram.
Neurons contain tail-like structures known as axons (labelled in the diagram above). These act as travelling channels for the electrical impulses of a neuron. Surrounding these axons are protective sheaths known as myelin, which act as insulators, allowing the electrical impulses to be sent down the axon quickly. Oligodendrocytes are a group of cells that support the neuron through the production of myelin.
The brain is covered with a blood-brain barrier that is only permeable to certain molecules. Immune cells like T and B cells must have the right ligand or surface molecule to get through. A T-cell can get activated by something it encounters once it is in. In the case of MS, it is activated by myelin. Once activated, it changes the blood-brain barrier to express more receptors, leading to immune cells getting in more easily. When these immune cells enter, they perceive the myelin as unfamiliar and therefore release cytokines like IL-1 and IL6, TNF alpha, and interferon-gamma. The cytokines also attract B-cells and macrophages (as part of the inflammatory reaction). B-cells make antibodies that mark the myelin sheath proteins. Then, macrophages use those antibody markers to engulf and destroy the oligodendrocytes, leading to no myelin on the neurons, which leaves areas of scar tissue (aka plaques or sclera). These attacks take place in bouts meaning that the regulatory T-cells might come and calm down the other immune cells, resulting in a reduction in inflammation. Early on in multiple sclerosis, the oligodendrocytes heal and extend out new myelin to cover the neurons, which is also known as “remyelination.” But over time, the oligodendrocytes die off, meaning that remyelination stops, causing irreversible damage.
These changes affect the function of different areas of the brain, such as the Frontal Lobe which covers the prefrontal area, premotor area, and motor area. The motor cortex controls movement functions, so, when MS disrupts this communication it leads to improper balance of the body. This area also includes functions such as thinking, planning, emotions, and behavior. MS causes the patient to suffer from sexual issues, mood swings, and other emotional behaviors. Next, we have the Temporal Lobe, which mainly controls memory and language understanding; meaning that if multiple sclerosis affects that area, it could lead to memory issues and slurred speech. Moreover, we have the Parietal Lobe, which controls perceptions, arithmetics, and spelling. That being said, if MS affects that area, it could lead to difficulties in finding the correct words and solving math problems. And last but not least, there is the Occipital Lobe, which controls vision. If there is an inflammation on the optic nerve, it could lead to blurred vision or seeing a black hole.
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