Absence of myelin sheath means that the nerve impulses become slow and sluggish.

失去髓鞘后，神经冲动传导会变得迟缓。

In particular, as you reach old age, the myelin sheath covering your axons wears down, and other neuronal structures degrade.

特别是，当你年纪大了以后，包裹轴突的髓鞘质会发生磨损，其它的神经元结构也会衰退。

Surrounding the axon is a myelin sheath, which is actually just insulation.

轴突周围是髓鞘，实际上只是绝缘层。

Those B-cells begin to make antibodies that mark the myelin sheath proteins, and then the macrophages use those antibody markers to engulf and destroy the oligodendrocytes.

那些B淋巴细胞分泌抗体，标记于髓鞘蛋白上，巨噬细胞利用抗体标志吞噬摧毁少突胶质细胞。

To be clear, these bacteria and viruses don't directly damage the myelin sheath, instead it's thought that they have antigens on their surface that looks similar to the lipid in the myelin sheath.

需要说明的是，这些细菌或病毒并不直接损伤髓鞘，相反，它们的表面抗原类似于髓鞘的脂质。

Once activated, the B-cells make antibodies that mark the auto antigens and the macrophages use those antibody markers to bind to and strip the myelin sheath off of the peripheral neurons.

一旦被激活，B细胞产生识别抗体与自身抗原结合，而巨噬细胞识别、结合抗原抗体复合物，清除周围神经元上的髓鞘。

As a result, immune cells mistakenly attack and destroy the myelin sheath and this is called molecular mimicry, because from the perspective of the immune cells a host substance is mimicking a foreign protein.

因此，免疫细胞会错误地攻击、损伤髓鞘；由于自身物质和细胞外来蛋白具有相似抗原表位而导致免疫细胞攻击自身，被称为分子模拟。