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B1 中級 英語 11:16 Educational

Multiple sclerosis - causes, symptoms, diagnosis, treatment, pathology

Osmosis from Elsevier · 2,781,282 回視聴 · 追加日 2ヶ月前

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00:04

Multiple sclerosis is a demyelinating disease of the central nervous system, which includes

00:09

the brain and the spinal cord.

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Myelin is the protective sheath that surrounds the axons of neurons, allowing them to quickly

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send electrical impulses.

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This myelin is produced by oligodendrocytes, which are a group of cells that support neurons.

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In multiple sclerosis, demyelination happens when the immune system inappropriately attacks

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and destroys the myelin, which makes communication between neurons break down, ultimately leading

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to all sorts of sensory, motor, and cognitive problems.

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Now, the brain, including the neurons in the brain, is protected by things in the blood

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by the blood brain barrier, which only lets certain molecules and cells through from the

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blood.

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For immune cells like T and B cells that means having the right ligand or surface molecule

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to get through the blood brain barrier, this is kind of like having the a VIP pass to get

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into an exclusive club.

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Once a T cell makes its way in it can get activated by something it encounters - in

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the case of multiple sclerosis, it’s activated by myelin.

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Once the T-cell gets activated, it changes the blood brain barrier cells to express more

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receptors, and this allows immune cells to more easily bind and get in, it’s kind of

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like bribing the bouncer to let in a lot of people.

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Now, multiple sclerosis is a type IV hypersensitivity reaction, or cell-mediated hypersensitivity.

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And this means that those myelin specific T-cells release cytokines like IL-1, IL-6,

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TNF-alpha, and interferon-gamma, and together dilate the blood vessels which allows more

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immune cells to get in, as well as directly cause damage to the oligodendrocytes.

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They cytokines also attract B-cells and macrophages as part of the inflammatory reaction.

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Those B-cells begin to make antibodies that mark the myelin sheath proteins, and then

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the macrophages use those antibody markers to engulf and destroy the oligodendrocytes.

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Without oligodendrocytes, there’s no myelin to cover the neurons, and this leaves behind

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areas of scar tissue, also called plaques or sclera.

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In multiple sclerosis, these immune attacks typically happen in bouts.

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