The loss or damage of myelin, the protective coating around nerve fibers, which prevents nerves from sending signals properly.
From demyelinate plus -ion (noun suffix). Myelin from Greek myelos 'marrow,' referring to the white fatty substance. The prefix de- means removal.
Demyelination in the brain is what makes multiple sclerosis so serious—once those protective sheaths are stripped away, your nervous system can't communicate efficiently, causing all sorts of symptoms!
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