DEVELOPMENT OF
MYELINATION AND AXON ENSHEATHMENT
Myelination requires a cooperative
interaction between the neuron and its myelinating support cell. Unmyelinated
peripheral axons are invested with a single layer of Schwann cell cytoplasm.
When a peripheral axon at least 1 to 2 µm in diameter triggers myelination, a
Schwann cell wraps many layers of tightly packed cell membrane around a single
segment of that axon. In the CNS, an oligodendroglia cell extends several arms
of cytoplasm, which then wrap multiple
layers of tightly packed membrane around a single segment of each of several
axons (or occasionally two autonomic preganglionic axons). Although myelination
is a process that occurs most intensely during development, Schwann cells may
remyelinate peripheral axons following injury, and oligodendroglial cells may
proliferate and remyelinate injured or demyelinated central axons in diseases such as multiple sclerosis.
