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I always thought the silver colour specific to nerves was due to the myelin sheaths, but I've observed that unmyelinated C fibres display that same silvery appearance. Where does this colour come from? And can you distinguish myelinated from unmyelinated fibre bundles with the naked eye from their colour?

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  • $\begingroup$ I don't know if I've heard "silver" as a color description for nerves of any type..white maybe in the context of white matter? Where are you seeing C fibers? $\endgroup$ – Bryan Krause Dec 18 '17 at 21:15
  • $\begingroup$ So I'm taking this from experiments done in animals. The spinal cord basically looks like a big, thick, silver straw (I always looked at the dorsal half, so including the dorsal columns which are Abeta fibres). I recently had a look at nerve around the splenic artery (which consists of C fibres almost exclusively). All these nerve to me look like silver shiny straws. I would love to attach some photos but I'm not sure that's appropriate... $\endgroup$ – Moppentapper Dec 19 '17 at 22:49
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Short answer
I think the whitish color is due to the outer layer of nerve bundles: the epineurium. This surrounds all nerves, whether they contain myelinated fibers, unmyelinated fibers, or both.

Background
Nerves are bundles of axons (Fig. 1). Whether the axons are myelinated or not, the gross anatomy is similar; axons within a nerve are bundled into fascicles and surrounded by perineurium. Those fascicles are again bundled up and surrounded by epineurium. It is this epineurium that you probably are seeing and it has a whitish appearance (Fig. 2).

The surface of a nerve therefore does not contain myelin; myelin is present around individual axons and is not exposed. Hence, whether a nerve contains myelinated axons, unmyelinated ones, or both will not determine its outward appearance.

nerve
Fig. 1. Anatomy of a nerve bundle. source: EasyNoteCards

epineurium
Macroscopic view of a nerve targeted for epineurial repair. source: wikipedia

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    $\begingroup$ Ah that makes sense to me, thanks a lot for this detailed answer @AliceD ! $\endgroup$ – Moppentapper Jan 14 '18 at 3:54

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