[MUSIC] So remember that the glial cells that make the myelin, they're different types that make it in the central nervous system and in the peripheral nervous system. And because of that, people get a demyelinating disease, get it either in the central nervous system or in the peripheral nervous system, but not in both. So the problem is either in the oligodendrocytes and the interaction between the oligodendrocytes and the axon, in which case you get a central demyelinating disease, and the most common by far is multiple sclerosis. Or there's a problem in the Schwann cell and its connection to the axon, and in that case you can get a variety. There are a diverse group of hereditary neuropathies called Charcot-Marie Tooth, these are demyelinating diseases, they're inherited and they typically progress and become worse with time. There's also an acute demyelinating disease called Guillain–Barré, which typically has a very quick onset, it's inflammatory, and luckily it goes away after a while. So what are the symptoms? Well from our perspective, the symptoms is that the neural code is disrupted anywhere there is demyelination. So demyelination in the peripheral nervous system is mostly gonna affect motor axons, cuz they conduct, they transfer information the fastest. So these are gonna have a lot of motor symptoms. But once we go to the central nervous system, there are axons all over, there are myelinated axons all over that do all manner of things. And the symptoms that a person gets with multiple sclerosis will entirely depend on which axons are affected. Now there are axonal groups that are more typically affected than others in multiple sclerosis, but there's no group that's always affected, and there's no group that's immune from the effects of multiple sclerosis. So the effects of multiple sclerosis are at a basic level to disrupt the neural code. But the actual symptoms that will result from that disruption are going to be individual across the group. Okay, so in the next module what we're gonna do is we're gonna clarify this difference between the central nervous system and the peripheral nervous system. [MUSIC]