Glial wrapping

One example of Na channel plasticity in central pathways subsequent to a non-ion channel gene deletion is revealed by analysis of the mutant mouse shiverer, which bears a major disruption of the myelin basic protein gene, leading to absence of the glial-specific intracellular membrane protein myelin basic protein (MBP) (Roach et al 1985). Lack of MBP prevents developmental formation of the major dense line essential for the compaction of glial wrappings that form the mature myelin sheath. As a result, large calibre axons in the shiverer brain are... 

The glial cells support the neurons physically. Certain glial cells (oligoden-droglial cells) synthesize myelin, a fatty insulation layer wrapped around the axons. Myelin is necessary for the so-called saltatory conduction of electrical... 

Myelin A segmented laminated lipoprotein sheath formed by glial cells (oligodendrocytes and Schwann cells). It is wrapped round the axon and acts as a biological insulating material. 

Figure 14.4 Different types of glial cells. Astrocytes connect capillaries and neurones. Fibrous astrocytes, with less branching and more filamentous processes, occur mainly in white matter while protoplasmic astrocytes are located principally in the grey matter. Oligodendrocytes form the myelin sheath by wrapping themselves around axons. The connection between the myelin sheath and the oligodendrocyte is permanent and provides material for the myelin sheath. Microgliocytes (microglia) are the phagocytes of the nervous system. The ciliated ependymal cells line the cavities of the central nervous system.

Astrocytes. Astrocytes constitute about 85% of all glial cells in the CNS thus their numbers surpass all other cell types, including neurons. Occupying this large fraction of total neural mass, it is perhaps not surprising that astrocytes maintain connections with both microvasculature and neurons. This positioning puts them in immediate contact with the incoming source of most neurotoxicants, the blood. Consequently, part of the protective function of astrocytes is their critical role in the formation of the blood-brain barrier (further discussed in Section 31.4.2.2). Astrocyte endfeet (the widened ends of astrocyte projections) wrap around capillaries and encapsulate... 

The myelin sheath Is a stack of specialized plasma membrane sheets produced by a glial cell that wraps Itself around the axon (Figure 7-39). In the peripheral nervous system. 

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