Myelins collapse

Several other diseases exist which can destroy the myelin sheath. Many are a result of viral infections or the body s immune response to a bacterial infection. Guillain-Barre syndrome causes numbness and paralysis starting at the extremities radiating into the trunk of the body where it can cause complete respiratory collapse. Guillain-Barre has occurred in senior citizens who have been given flu vaccinations. The virus used in the vaccination may be attenuated (diminished in virility but not "killed") and still be capable of causing an infection. 

Several aspects of Schwann cell metabolism emerge as potential points of vulnerability to toxicants. The Schwann cell perikaryon (cell body) supports an enormous peripheral structure, the myelin sheath, which, if unwrapped, would dwarf the body of the Schwann cell (see Figure 30.4). Thus, as in the case of axonal transport in neurons, there may be specialized processes involved in supporting the topologically distant myelin. Furthermore, myelin has a specialized lipid and protein composition and a relatively rigid and ordered structure as compared to other membranes. Metabolic perturbations that potentially cause alterations in the composition of lipids and proteins assembled to form this membrane may cause destabilization and collapse of the myelin membrane. In this context, myelin might be much more vulnerable than plasma membranes of other cells. 

All three of these proteins are present in the lung. The lamellar bodies are secreted into alveolar lumen where they are transformed into an extracellular form of surfactant that has a quadratic lattice structure called tubular myelin. The three-dimensional tubulin-myelin structures spread in a monolayer at the air-liquid interface. This spreading decreases the surface tension, prevents alveolar collapse at the end of expiration, and confers mechanical stability to the alveoli. The surfactant system is in a continuous state of flux, and surfactant is recycled by uptake... 

Myelins have also been observed to collapse when an intermediate sponge phase is present between the lamellar phase and the micellar phase (47). After the formation of the myelins sponge phase is observed to from at the surface (Figure 3). The delayed formation of the sponge phase in this case is consistent... 

Ewes fed a diet deficient in copper may give birth to abnormal lambs (49, 50). The newborn lambs are unable to stand to obtain milk from their dams. Those that can get up sway and collapse their hind quarters seem paralyzed ( Swayback ). The brains of the affected animals show areas of de-myelination in the white matter, which may be of microscopic size or appear as a gross cavity. In the spinal cord secondary degeneration of the motor tracts has been found (51). The incidence of this disease can be greatly reduced among the offspring, when the ewes receive salt licks with copper supplements. 

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