Hello all,
Just chiming in with a quick question that came up while talking about squid: I know that squid possess giant axons because theirs’ aren’t sheathed in myelin. So, naturally, we wondered how big the giant axons are on a giant squid. Is it giant squared or what? Are there any photos available?

cheers,
thom.

Hello all,
Just chiming in with a quick question that came up while talking about squid: I know that squid possess giant axons because theirs’ aren’t sheathed in myelin. So, naturally, we wondered how big the giant axons are on a giant squid. Is it giant squared or what? Are there any photos available?

cheers,
thom.

JZ Young wrote once that he was frequenly asked if giant squids had a "more giant" giant axon than normal squids, and that they don't (well, I assume it's longer, but apparently it's not thicker). I think this was in the special "we like JZ Young" issue of the proceedings of the Royal Society... I don't have the reference handy.

JZ Young wrote once that he was frequenly asked if giant squids had a "more giant" giant axon than normal squids, and that they don't (well, I assume it's longer, but apparently it's not thicker). I think this was in the special "we like JZ Young" issue of the proceedings of the Royal Society... I don't have the reference handy.

That makes sense, as a thicker axon perhaps doesn't increase conduction speed anymore, after a certain point. It would still be one heck of a nerve fibre though... I wonder what that means in terms of reaction time for the giant squid, and it's feeding habits.

That makes sense, as a thicker axon perhaps doesn't increase conduction speed anymore, after a certain point. It would still be one heck of a nerve fibre though... I wonder what that means in terms of reaction time for the giant squid, and it's feeding habits.

The giant axon is also primarily part of the escape reflex in small squids-- it seems likely that the "jet rapidly away" mechanism is less useful for giants, both because there are many fewer things that it needs to escape from, and because as it gets larger, the speed at which it can jet is probably limited a lot more by muscle and water properties than by how long it takes to tell the mantle to start contracting...

Of course, it's probably still quite useful in juvenile architeuthis that are similar in size, shape, and lifestyle to the smaller squids that people look at the axons in...

The giant axon is also primarily part of the escape reflex in small squids-- it seems likely that the "jet rapidly away" mechanism is less useful for giants, both because there are many fewer things that it needs to escape from, and because as it gets larger, the speed at which it can jet is probably limited a lot more by muscle and water properties than by how long it takes to tell the mantle to start contracting...

Of course, it's probably still quite useful in juvenile architeuthis that are similar in size, shape, and lifestyle to the smaller squids that people look at the axons in...


Too bad for the adult squid when it meets the whale that does it in.. Even if it were to get a myelin sheath for christmas.
(I always did think that Darwin looked like santa claus)

Too bad for the adult squid when it meets the whale that does it in.. Even if it were to get a myelin sheath for christmas.
(I always did think that Darwin looked like santa claus)

It would be interesting to know about whale hunting and archi escape strategies in the wild-- I wonder how their sprint and duration swimming speed compares. Even though the huge squid eyes can see better than most things down there, I bet the sonar helps a lot in the whale being able to track the squid, even if it does a quick escape jet...

I don't have the reference handy.

is this it?

Young. J.Z. (1939) Fused neurons and synaptic contacts in the giant nerve fibres of cephalopods. Philosophical Transactions of the Royal Society of London B, 229, 465-603

are J.Z. and R.E. Young related?

Im unsure if the giant squid have even larger giant axons then smaller squids or that they just may have more of them while they are the same size. But if they are the same size and they have more of them, I believe this would allow for a larger range of behaviour because they can create more neural pathways given the amount of space available. Mylenation gave other animals (like us) the ability to have fast conduction but keep very small axons allowing for much more complex networks. The giant axon found in cephalopods was a alternative solution in which I imagine limited the evolutionary potential of cephalopods..well in an anthrompomorphic way. In other words, I think if they developed myelination instead of giant axons, they may have evolved to be even smarter and more complex then they already are..

Was just reading on this very thing last week for my boss (she wanted the diameter of the giant axon.......~1mm if anyone's interested :grin: ) Anyway I was reading in Hanlon & Messenger (Cephalopod Behaviour) that there are 1st, 2nd, and 3rd order nerves and the later two are much finer and to do with day to day movement etc and the 1st order were for the escape reponse and thus the impulse moves faster in them. Interesting stuff.....

J

is this it?

Young. J.Z. (1939) Fused neurons and synaptic contacts in the giant nerve fibres of cephalopods. Philosophical Transactions of the Royal Society of London B, 229, 465-603

I think it's a lot newer than that, 70s or 80s. There was one issue of the Royal Society rag where they had kind of a retrospective of JZ Young's work, and he talked about the neuroanatomy of some cephs that he hadn't published about elsewhere, like Archi and Vampy...

are J.Z. and R.E. Young related?

I have no idea, but they both publish cool stuff...