local anesthetic, Myelinated vs unmyelinated

[anbuitachi]

First aid says meylinated fiber is blocked first before unmyelinated. In class i learned that unmyelinated is more senstitive to local anesthetic than myelinated. The explanation is that there's less to penetrate..

I don't see this in the Errata so I'm assuming first aid is correct, but i'm not sure why. Can someone explain this please

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[beatsbydre]

I think you are confusing two different concepts here. Size and myelination. Smaller fibers are blocked first. However, they are often unmyelinated. Larger fibers are blocked last. However, they are often myelinated.

If size remains the same, the myelinated fibers get blocked first. And for general review, it's autonomics first, sensory second, and motor last in terms of blocking.

 

[anbuitachi]

what is teh concept to myelinated fibers blocked first w/ same diameter?

 

[CaptainSSO]

what is teh concept to myelinated fibers blocked first w/ same diameter?

Probably the lipophilicity (don't know if that's actually a word) of the local anesthetic.

 

[beatsbydre]

what is teh concept to myelinated fibers blocked first w/ same diameter?

I think it has to deal with the nodes of Ranvier and the concentration of Na+ channels there. With the unmyelinated fibers, the Na+ channels are not as concentrated and it takes longer to take one fiber out.

 

[CaptainSSO]

I think it has to deal with the nodes of Ranvier and the concentration of Na+ channels there. With the unmyelinated fibers, the Na+ channels are not as concentrated and it takes longer to take one fiber out.

Yeah. Or that.

 

[anbuitachi]

thanks !!