= Myelination
<Myelination> forms layers of <myelin> around segments of an <axon>. <Oligodendrocytes> produce these sheaths in the <central nervous system>, while <Schwann cells> do so in the <peripheral nervous system>. Gaps, each called a <node of Ranvier>, allow <action potentials> to be regenerated between insulated segments, supporting <saltatory conduction>.
The arrangement affects when signals reach their targets, not just whether an <axon> is present. In mice, altered visual experience shortened segments wrapped in <myelin> along the <optic nerve> pathway and was associated with slower conduction along the <optic nerve>. The observations connected environmental input, <myelin> sheath geometry and a measured physiological consequence.<Dynamic Modulation of Myelination in Response to Visual Stimuli Alters Optic Nerve Conduction Velocity by Ainhoa Etxeberria and others>[Journal of Neuroscience 36, pp. 6937–6948; visual deprivation, internode length and conduction measurements]{ref} This experimental result does not imply that more <myelin> always produces a uniformly faster or better-performing <nervous system>; segment geometry and the timing required by a circuit matter.
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