Neurological Question

tonmo

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Re: Neurological Question

Armstrong said:
Start at http://www.dictionary.com, we'll be here when you get back! :wink:

A perfectly valid question that I look forward to an answer to (assuming one is out there... I mean, I wonder if a squid's axon were damaged, if it could even live long enough to allow it to regenerate....)

Page 50 of Richard Ellis' book on Giant Squid, in reference to Loligo:

A 1988 article on squids by Malcolm Clarke opens with these words: "To many biologists the squid conjures up a vision of an unusually large nerve fibre with graphs issuing from one end while elctrodes are applied to the other." The "unusually large nerve fibre" is another wonder of squid biology, for it can be one-tenth of an inch in diameter, as compared with the largest human axon, which is only one one-thousandth of an inch. The size of these giant axons enables the squid to transmit messages to its musclees substantially faster than any other creature; the squid's ability to respond to a particular stimulus can be almost instantaneous. For human neurological research, these giant axons are much easier to study than those of most other animals.
And in reference to Architeuthis on page 56:
It is not clear as to whether giant squid have giant giant axons. In his 1977 essay "Brain, Behaviour and Evoloution of Cephalopods," J.Z. YOung (who spent his fifty-year career concentrating on the neurology of squids and octopuses), having disected a specimen that washed ashore in 1933, wrote, "None of the nerves examined contained the exceptional large fibres reported by Aldrich and Brown (1967). We may conclude that Architeuthis is not an especially fast-moving animal. This would agree with evidence that it is neutrally buoyant with a high concentration of ammonium ions in the mantle and arms (Denton, 1974)."

It goes on a bit more about squid neurology; interesting stuff.
 

Steve O'Shea

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..... yes, even I'm a tad confused (which isn't saying much actually, I'm always confused). There was an article in Nature this past week too .... real pretty pics of developing squid - just don't ask me what language it was written in.
 

Steve O'Shea

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Howdo John; sorry, have a pdf only .... not sure what copyright laws I'd be breaching (if any) posting here. Technicalities. Spotcha on private e-
Ta
O
 
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NEW neurological question

I have a followup question for anyone out there that might know: Does anyone know the diameter of giant and/or colossal squid giant axons? My physiology class is kicking into gear, and I was thinking of a research paper topic. Thanks!

John
 
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Yeah, me too... I know that the giant axons are nonmyelinated and such, but I would like to know more to calculate conduction velocities and such. We have a paper due by May, and I'm kicking around the idea of doing a paper on squid (mostly because the class tends to focus on vertebrates! :twisted: )

Thanks!

John
 

Brown

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There is no doubt that squid and octopus nerves and axons regenerate (like most invertebrates) . Work by Young in the 70s and recently Packard on the nerve tract that contains the giant axons and chromatophore nerves shows that functional regeneration after a nerve section completes in 40- or so days depending on the time of year and temperature (degeneration occurs first of course). As to toughness, an isolated axon will survive for a couple of days but they don't survive stretching or bending well.
 

Brown

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What determines conduction velocity?

Conduction velocity in a 450 micron diameter axon would be about 18 m/s at 20 degrees. The range in nervous systems is from a few cm /s (pain fibres) 100 m/s myelinated nerve. There are several ways to 'speed up' conduction velocity (speaking in terms of evolution and biophysics). The two main ones are …

1. Decreasing the longitudinal axonal resistance. As the axoplasm resistance is constant this improvement can only be achieved by increasing the diameter of the axon (in the way that a length of copper of large diameter is of lower resistance than one of small diameter). If you like equations, this means that conduction velocity is proportional to the square root of axonal diameter. Selection pressure for high conduction velocities has resulted in the appearance of giant axons.

2. Increasing the transmembrane resistance. This is achieved by wrapping the axon with more than one glial membrane= myelination. Mostly in vertebrate (but not all vertebrate nerve see slow conducting pain fibres) ns. Is also present in some invertebrates (but not cephs). Leads to salutatory conduction and high conduction velocities with small diameter fibres.

hope this helps
 

Steve O'Shea

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Looks like we have ourselves a new, resident neurological expert online; thanks for those words of wisdom (that went right over my head); I'm sure John (and others) will appreciate them.

Welcome to Tonmo, Dr Brown; I'm sure that you have expertise in other areas also.

Steve
 
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i know physciatrists and neurosurgeons that wouldnt understand that where did you get the degree ?!!!!! also doctor steve thats a bit of an understatment ! hail prof.brown :notworth:
 
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