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Here is a website I found with some basic information about Multiple Sclerosis, including the 4 most common courses that the disease usually takes:

http://www.nationalmssociety.org/site/PageServer?pagename=HOM_ABOUT_what_is_ms

Since MS is thought to be an autoimmune disease, I was surprised to learn that the replacement of myelin does seem to occur in the majority of patients (about 85% experience periods of relapse and remission).  Each demyelination can cause scarring of nerve tissue, which would explain why, even though myelin can be replaced, symptoms of MS tend to get worse over time.

I would also like to talk more about neuron structure (i.e. "what is 'the middle' of the system?") and the process by which action potentials are transmitted from one neuron to the next. 

Additionally, we have not yet discussed ion channels other than the "voltage-gated" type; I remember discussing stretch-gated ion channels in intro bio, and I think that these channels, which are responsible for some reflexes, could help to clear up some of the confusion about "voluntary" v. "involuntary" actions.