Description: Segment 1 McDonald begins by defining how demyelinating processes tend to go through phases of recovery, as with multiple sclerosis however, after each attack on the nerve fibres, recovery is never back to complete health. McDonald describes how he is going to discuss the damaging effects of demyelination on the nerves and whether or not remyelination plays a role in the recovery period. McDonald shows a large projection of nerve fibres and describes in detail their various parts. McDonald then looks at a further slide comparing demyelination with another nerve fibre abnormality, Wallerian degeneration. He explains the difference between the two processes. A further slide shows demyelination in the fibres of the optic nerve and McDonald describes how this has occurred due to optic neuritis. Time start: 00:00:00:00 Time end: 00:06:25:00 Length: 00:06:25:00 Segment 2 McDonald focuses on a series of animated diagrams detailing changes in electrical conduction due to demyelination. He describes these in detail, outlining how the changes occur. Time start: 00:06:25:00 Time end: 00:09:46:00 Length: 00:03:21:00 Segment 3 McDonald shows an animated diagram which details how nerve fibres transmit long trains of impulses through the nervous system. A further animated diagram is used to highlight how conduction velocity changes in demyelinated parts of single nerve fibres. This shows how demyelinating lesions give rise to nerve conduction block, thus problems of the central nervous system. McDonald then shows an illustration of the optic system, followed by a man having his optic nerve patterns recorded onto an averaging computer which measures them. McDonald describes the process. Time start: 00:09:46:00 Time end: 00:15:08:00 Length: 00:05:22:00 Segment 4 McDonald continues to focus on the optic nerve. He shows diagrams of optic nerve conduction in patients with optic nerve defects explaining what can be seen in each case. McDonald then moves on to discuss recovery or remyelination, in which patients suffering from diseases such as multiple sclerosis experience periods of remission. he shows a large slide projection which details the remyelination of nerve fibres. Time start: 00:15:08:00 Time end: 00:20:24:00 Length: 00:05:16:00