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Squid Spinal Cords

tonmo

Cthulhu
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I received the following email, and wanted to share it here, as requested.
Sir...


You must certainly have the answer...


... the squid which was studied at Wood's Hole (... which is 12 - 18 inches long) several decades ago had a "giant axon" which was 100 times larger than a human axon.


WAS THAT AXON "MYELINATED?"


Does the Wood's Hole squid have a spinal cord... or is the GIANT AXON the spinal cord?


..................


Does the Humboldt squid (... which can be 6 feet long) have a GIANT AXON?


A SPINAL CORD?


How large (... diameter) is the "MAIN NERVE" of the Humboldt squid?


...............


Does the Giant Squid (... the 30 foot long beast which was photographed in Japan in 2005) have a GIANT AXON?


A SPINAL CORD?


How large (... diameter) is the " MAIN NERVE" of the Giant Squid?


...............


Since myelin involves the "jelly roll wrapping of Schwann cells" I doubt that any of the three kinds of squids have MYELINATED MAIN NERVES.


.................


Herman Melville (MOBY DICK) wrote that the sperm whale spinal cord is 10 inches in diameter and 15-20 feet long.


Is this huge "MAIN NERVE" common to all the creatures which swim in very deep ocean waters?


,,,,,,,,,,,,,,,,,,,,


I am interested in these things because of my interest in the role of axonal microtubules in the quantum mechanics of the mind.


............




Could you post this E-Mail on your splendid web site?


...............




SORRY TO BOTHER YOU...




Richard Bergland MD
retired academic neurosurgeon...
... long ago, at Cornell, Penn State, Harvard, Oxford, Melbourne, etc.
 
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:welcome: Dr. Bergland.

Squid do not have a spinal cord. Their giant axon is not myelinated. If I can I will find a diagram of where their giant axon is situated in their body. They actually have two giant axons, one for each side of their body. I believe the axon was named because of its diameter.

Here is a link for a reference about giant squid axon. It is a little old, but I think most of the information is accurate.
Arnold, J. M., W. C. Summers, D. L. Gilbert, R. S. Manalis, N. W. Daw and R. J. Lasek. 1974. A Guide to Laboratory Use of the Squid Loligo pealii Woods Hole, MA: Marine Biological Laboratory. 74 pp.
https://darchive.mblwhoilibrary.org/bitstream/1912/224/9/chapter+5.pdf

Only vertebrates have some of their nerves myelinated. As I understand, myelin increases the speed of propagation along the nerve without having to increase the diameter.

I am not sure how accurate Herman Melville was in his facts about Sperm Whales but when the animal is 50 feet long, its spinal column would be large too.

I am sure there are other members who could give you a more detailed (and perhaps accurate) description.
 

monty

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Augmenting Cuttlegirl's responses, there is an article by JZ Young, I think in Proceedings of the Royal Society B, in which he says that giant squid giant axons are not particularly larger in diameter than the giant axons of smaller squids. In general, squid giant axons are quite different from spinal cords, since a squid giant axon is a single nerve, while a spinal cord is a bundle of many, many nerves.

I think the whale's spinal cord is much more like typical vertebrate spinal cords. However, in terms of "do all creatures of the deep have such a thing," at TONMOcon, William Gilly mentioned that there is a similar mechanism to the squid giant axon (and its associated stellate ganglion) in certain fish that seems to serve the same function: they both need to send a signal rapidly from the head to the tail in order to execute a rapid burst of speed as an escape mechanism. So there is some commonality.

I'm not aware of microtubules playing much of a role, quantum mechanical or otherwise, in axons... the propogations of action potentials along axons depends largely on the voltage gated ion channels in the axon's membrane, and the ion pumps that keep a difference in concentration of the sodium and potassium ions inside and outside the axon. Most of the tricky stuff in neurons happens in the dendrites, and a bit in the soma...
 

um...

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Microtubules are very important when it comes to extending axons, which is crucial because they don't work very well if they conduct action potentials to nowhere.
 

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