Does a lack of white matter in the brain cause movement disorders?

White matter refers to the myelin sheath around a nerve.

In the picture below, the top part shows a myelinated nerve - which looks like a long sausage. The spaces between each sausage link is called a node of Ranvier. The node is an open area - the only place on the axon where the exchange of Na+ and K+ ions) necessary to propagate an action potential) can occur. This means that for the action potential to travel down the nerve, it must “re-ignite” at each node. That makes it like an express train, with the action potential jumping from node to node.

The bottom portion of the picture is an unmyelinated nerve. It is more like a local train, making all the stops. This means the impulse travels more slowly.

Because various functions require the contributions of hundreds of nerves, the slowing down of too many of them may mean the loss of the function- as happens in multiple sclerosis.

The process of myelination occurs with development. All the milestones, sitting up, standing, walking, talking etc, are a consequence of myelination. Loss of myelin means a reversal of ability. The genetic disorder adrenoleukodystrophy (ADL) portrayed in the movie “Lorenzo’s Oil” renders the victim a “basket case”, unable to move, speak, see, eat etc. It is always fatal.

A familiar example of a myelinated vs unmyelinated experience occurs in the pain system. If you hit your finger with a hammer, you first experience “fast pain” which travels quickly to your brain along a myelinated pathway. The pain is short lasting and precisely localized. It will cause you to stop hammering and to swear at yourself for being a jerk. It also gives you enough time to run to the faucet and start the cold water running in preparation for the arrival of the slow pain.

Slow pain travels along an unmyelinated system and stops off in your limbic system to make you feel sorry for yourself- maybe even cry. Because the pathway is recurrent (meaning it recycles the activity), it doesn’t go away anytime soon. In addition, it is less localized so you become protective, not just of your finger, but your whole hand. (In fact, some of these circuits cause you to withdraw your entire limb out of harm’s way and to limp).

(Because anesthesia affects unmyelinated nerves, this explains why blocking them eliminates pain)

Your question regarding which function affected with demyelination depends upon the LOCATION of the myelin loss. Whichever subway line switches from express to local, means that those passengers are the ones to be late.

An early symptom of multiple sclerosis (MS) is blurred vision when exercising (because the vision fibers are demyelinating) or dizziness when immersed in a hot tub. Heat exacerbates demyelinating disorders because the normal nerves conduct MORE efficiently when warm, giving them a greater advantage over the damaged nerves, which by contrast are slower still.

Reference: Joyce Schenkein