Myelin sheaths are one of the key reasons our body is able to function so well, however not all animals evolved this mechanism. Squid, instead of using myelin sheath instead of extra large neurons with axons called...large axons. Now I was just wondering if anyone in the neurology field could tell me what might happen if we were able to get extra large neurons to ALSO have a myelin sheath. Would the transmission rate of the nerve signal move even faster then in the current two systems? FYI, by having a large axon the transmission speed if also speed up but I forget the exact name of the effect that results in this increased speed.

Not a neurlogist am I (yoda talk ;) ) but let me see what your getting at:

1. Use Myelin to insulate the axons and prevent ions from leaking out and reducing the ion differential.

and/or

2. Just have very wide axons that some how retain their ions by shear size and width?

Actually the larger the diameter of the axon, the faster the action potential moves. Like I said, has some electro-mumble jumbo word that I can't recall, and my neurology book is at home.

Really? I would think it would be slower considering there reduce surface area per volume. The ionic pulse (not electrical) is the rapid opening of pores and pumps on the axons that switch calcium and potassium ions from inside the axon to the outside and vise versa. I am not a neurologist so if I’m wrong about which ions don’t get mad at me!

I thought it was sodium and potassium. ;)

Hey I know calcium is one of them!!! Which is outside the axon and which is inside I can't remember: youngbiologist should give us the details.

neuroscientist i am. cognitive though, not molecular.

that's an interesting question. in theory i would think that it would be faster.
but i don't know all the details of neurotransmission so if it would actually work in reality i don't know.

Do you know how squids and humans compare in speed?

Quoted from http://educ.queensu.ca/~science/main/concept/biol/b07/B07CDC10.htm
2. Sodium-potassium pumps actively transport Na+ out of the cell and K+ into the cell to generate steep gradients.

Well I'll be a monkeys uncle!, It is Na and K then what the hell is Ca for in the nervous system? It was for something important but I can’t remember.

Na+ and K+ are involved in sending the action potential down the axon. Ca- then is released which leads (via various Ca dependant protiens) to the release of the neurotransmitter. Ca- also plays an important role in determining whether or not an action potential is initiated- it is sometimes allowed into the cell via inhibitory neurotransmitters, thereby hyperpolerizing the cell and preventing the cell from "firing".
---------------------------------------

As mentioned, the action potential can be sped by both myelin sheaths and axon diameter. Having a larger axon AND a myelin sheath will speed up the transmition further up to a point. (Obviously, having ever larger and more myelinated axons will not keep speeding it up indefinitely- but some speed can be gained.)

thx for the info Cog.

Still Electrons move ~1,000,000 times faster then Ions.

So that begs the question, how come our own nerve cells haven't evolved to be as large as the ones found in squid. While we do have single neurons that can be as long as a meter, I was under the impression from the liturature that our nerves were thinner then that of the squid. If I recall correctly, our transmission range is about 110 m/s( just heard this at my advanced cell bio), and the squid has about a 80 m/s transmission rate. Do you think the reason why our nerves don't have both adaptations may simply be cause of insignificant evolutionary pressure?

Originally posted by youngbiologist
So that begs the question, how come our own nerve cells haven't evolved to be as large as the ones found in squid. While we do have single neurons that can be as long as a meter, I was under the impression from the liturature that our nerves were thinner then that of the squid. If I recall correctly, our transmission range is about 110 m/s( just heard this at my advanced cell bio), and the squid has about a 80 m/s transmission rate. Do you think the reason why our nerves don't have both adaptations may simply be cause of insignificant evolutionary pressure?


Good question. I do know that the speed they transmitt at should not alway be as fast as possible. There are some neurons (nociceptors), for example, that will have slower and faster speeds for different purposes. The faster nociceptors give rise to sharp pain immeadiately (so you can get away from the pain quick), while the slower, unmyelinated kind produce long lasting burning pain (so you can favour the damaged body part).

I don't think I answered your question. That is because it exceeds the extent of my knowledge. :)

I think it became difficult for evolution to increase the speed anymore with out having negative side effects. Evolution works to make something work well but not perfect... there is a point were something to perfect can become a detriment. Growing and powering such large neurons could become a problem. Already 1/3 of all energy produced in the human body goes to K/Na pumps in the neurons!

Something else (I should have thought of earlier)-


The critical factor is how many times per second a cell can "fire". After each time, there is a refractory period. My guess is that although the speed of transmition of a particular action potential might increase, the firing rate as a whole will not. I vaugely remember hearing somewhere that the firing rate of some cells is prevented only by the need for refraction. (This doesnt really explain a whole lot in terms of your question, but it is something to keep in mind.)

What is the fasts firing rate in humans? I think retinal neurons do about a max of 30per second.

Originally posted by youngbiologist
So that begs the question, how come our own nerve cells haven't evolved to be as large as the ones found in squid. While we do have single neurons that can be as long as a meter, I was under the impression from the liturature that our nerves were thinner then that of the squid. If I recall correctly, our transmission range is about 110 m/s( just heard this at my advanced cell bio), and the squid has about a 80 m/s transmission rate. Do you think the reason why our nerves don't have both adaptations may simply be cause of insignificant evolutionary pressure?

speculation:

it is probably one of those chance things. Both squids and vertebrates needed a solution for fast neurons. In squids it was easiest to make large neurons. In vertebrates there already might have been some like myelin. That got adapted to make neuronal signals faster. Both systems attained the speeds they required and hence there was no need to evolve even faster ones.

>> Both systems attained the speeds they required and hence
>> there was no need to evolve even faster ones.

Who said that we were done evolving? We haven't yet had the NEED for these superfast neurons, but I suspect that we will before long.

I say we start engineering neurons that use electrical impulse instead of ionic.

umm.....:bugeye:

but I suspect that we will before long.
Out of curiousity, what is leading you to suspect that?

who are you talking to?

Originally posted by eaxelrod


Who said that we were done evolving? We haven't yet had the NEED for these superfast neurons, but I suspect that we will before long.

i said they are done evolving because they haven't evolved any further since millions of years.

Ever increasing technological demand may be pushing the limits of the human brain... that and cybernetics is going to do for us in a few decades what natural evolution could not in a many eons!

>> I say we start engineering neurons that use electrical impulse
>> instead of ionic.

You first

Love to

>> i said they are done evolving because they haven't evolved
>> any further since millions of years.

Our neurons may or may not have evolved in the past few million years, we have no way to tell. But as we progress through the information age, we will be subject to more knowledge and will require more neural 'bandwidth' than ever before. Biological need is what spurs evolution, and it wasn't until the present day that we actually NEED greater bandwidth.

Because of our current need for more processing power -- the societal situation isn't getting any better for us puny humans, so we will need long term adaptations.

>> cybernetics is going to do for us in a few decades what
>> natural evolution could not in a many eons!

Speaking of cybernetics:

"A HALF CENTURY OF ARTIFICIAL-SIGHT RESEARCH HAS SUCCEEDED. AND NOW THIS BLIND MAN CAN SEE."

http://www.wired.com/wired/archive/10.09/vision.html

Agree, except short term modification would be quicker and better.

-Bandwidth refers to a range of connection or how much can be procesed at once.
-Speed of processing is a sub-unit of bandwidth
-Faster neurons would mean quicker response times and faster thoughts, but not necessarily more storage capacity or enlightenment.

Originally posted by eaxelrod
>> i said they are done evolving because they haven't evolved
>> any further since millions of years.

Our neurons may or may not have evolved in the past few million years, we have no way to tell.

maybe you have no way to tell, but I have...if two distinct species have the same nearons it is likely that their ancestor had them. Then look at when they separated and voila...you have an answer. Science is simple isn't it.

hmm, some nice posts out there. Yeah, using an electrical signal instead of the action potential of a neural signal would be better. However it would require metalic atoms, and only recently was an animal observed with the ability to manipulate large amounts of metal. Some small insect was found about a year ago to have jaws hardened by copper, this is really insteresting. Having a copper based system for sending signals would be quicker, but you would be more prone to electromagnetic radiation. Right now we can aim a HUGE magnet and manipulate the neurons, but if your neural system is largely made out of copper your more sensitive. However, the increased sensitivity could be much smaller, I just don't know. Now that I think about it...long coiled coil filaments of alpha helix covered with extensive amounts of copper ions at the center....hmm. Yeah, our current tranmission speed is WAY slower then what simple wiring would do.


The biggest thing holding back our mental evolution is women. Well, specificially the size of their hip bone. Right now our big brain has alot of difficutly getting through the birth canal, and thus is limited in size. However...cesarian sections are becoming more popular so this might have an effect...While natural selection doesn't really have a role in human society, there are still sexual preferances. Guys/Girls with brains are usually considered better suitors, so this explains the continued evolutionary pressure for more intelligence.

Yes but the instinct to F|_|[K the pretty is still much stronger. Braun still bets brains in getting women in bed with you.

If we engineer the skeleton to be made of a biologically assembled metal alloy then the skull will be a metal case that would easily deflect all EMW. We would still need ionic neurons for motor control though because of them being unshielded.

since when did doing the dirty MEAN having offspring. With birth control it doesn't, as such when women want to commit they try to find the best suitor.


My brief idea was to have the new flexible copper filaments to be within the neural axon, the axon potential would just start an electrical signal that transfered faster down the copper filaments. You would still have the normal neural synapses among other things...

>> if two distinct species have the same nearons it is likely that
>> their ancestor had them. Then look at when they separated
>> and voila

It may be likely that their ancestors had the same type of neurons, but that is not proof, it is evidence.

Is it not possible that the two different species developed strikingly similar neurons simply because those neurons are most efficent for their enviornment?

You never saw that show on TLC (or was it discover) about the surprisingly high rate of cheating among women. A women may marry a rich, successful and intelligent guy but that does not mean she is not f|_|[king the good looking milk man.