Why is Myelin used as a term to mean the Myelin Sheath as opposed to the proper term?

It is apparent to me that Myelin is the substance itself regardless of structure and the Myelin Sheath is the structure around the axis to insulate Electro-Chemically the nervous system composed of this substance.

But Media and Physicians frequently use Myelin instead of Myelin Sheath as opposed to textbooks that make the distinction


1 Answer 1


As Wikipedia points out:

Myelin is a lipid-rich (fatty) substance formed in the central nervous system (CNS) by glial cells called oligodendrocytes, and in the peripheral nervous system (PNS) by Schwann cells.

When referring to the sheath, you are referring to the covering which is made of myelin.

Myelin sheaths are sleeves of fatty tissue that protect your nerve cells from damage (WebMD).

The thing is that myelin formed in the CNS and PNS is only used in the form of a sheath to protect your nerve cells, so when physicians refer to the myelin, they are referring to the sheath.

With demyelination, the integrity of the sheath is being compromised.

  • $\begingroup$ So it seems I was right. But my question was not what Myelin is as opposed to the Sheath. But rather asking for an explanation of the weird fact that Physicians and Media use Myelin to mean the specific structure. Demyelination is not weird because if something loses it's myelin it could not possibly keep its myelin sheath made out of that same myelin that was supposed to be Lost. $\endgroup$ Aug 19, 2019 at 0:07
  • $\begingroup$ Might be worth adding that myelin is really only found in sheaths...so, referring to myelin is basically the same thing as referring to the sheath. $\endgroup$
    – Bryan Krause
    Aug 19, 2019 at 0:12
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    $\begingroup$ @BryanKrause - I agree and added that in for clarity. $\endgroup$ Aug 19, 2019 at 8:40
  • $\begingroup$ @ChrisRogers This does not change the fact that textbooks make a clear distinction. Myelin can be extracted from the sheath and it will still be myelin. It will not be the Sheath. $\endgroup$ Aug 19, 2019 at 19:21
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    $\begingroup$ @GeorgeNtoulos Can you point to a single example where someone refers to "myelin" where they are not referring to the sheath? Myelin is not a special substance, it's phospholipid membrane. If it wasn't in a sheath you wouldn't call it myelin. One could argue that calling it a "myelin sheath" is redundant, but sometimes redundancy is accepted in language. $\endgroup$
    – Bryan Krause
    Aug 19, 2019 at 20:40

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