@watsonic Ahh. You mean what if in a long axon the first AP has not reached the synapse but the soma/dendritic region is already repolarized?

@watsonic see the edit. I hope it answers your question.

wait wait wait - the sciatic nerve fibers running from the base of the spinal column to the toes are about a meter long! sciencedaily.com/articles/a/axon.htm So this should be more than sufficient to physiologically evoke multiple APs in the axon.

@ChrisStronks I don't know about its length. I might have read incorrectly. Edited

@ChrisStronks But it is unbelievable to me that a single axon can be that long. Lot of delay in plastic transcriptional events. Perhaps they do not undergo such events a lot.

It is unbelievable! But true :) You have my word on it. That's how the system works. If you need more distance to cover, elongate the axon :)

You could easily adapt your answer by filling in 1,000,000 um and raise some awesome number of simultaneous APs!

Anyways.. I edited the answer. but I am surprised. Why should a single axon be that long

It has to cover the distance between spinal chord to end target. The longest distance from the spine exit point and peripheral target is the sciatic nerve heading to the big toe

It's just how them peripheral system works.

his means the nucleus would be overburdened to cope up with extensive turnover. Also a single injury or just a temporary shock would fuck up the entire conduction channel

Wouldn't it be better to have many neurons serially connected by gap junctions

It does. it is not surprising that circulation issues (diabetics) loose their perception in their toes and extremities first. These are the most sensitive neuronal connections and are hit first

I think theoretically you are right, but evolution often just increases something that is there. Take the cortex, it is easier to increase its size by increasing its thickness. Yet nature keeps on adding sulci and gyri

Evolution takes the easiest way, which is not always the most robust one

that is true.. But selection pressure can act against it. Imagine a single injury or just exhaustion causing amalfunction.

Yep, my reasoning is not water tight. Yet the fact stands that 1-meter axons occur :)

WAIT! I got it! Synapses are the slowest component in a neuronal pathway. each one of them adds 10 ms

reflexes are going to suffer in your scenario, which is definitely evolutionary pressure

Yeah I accept that fact.. Thank you. I had read this sometime when I was in school. But when I grew up i forgot it perhaps I reasoned that it is one of the lies that they tell you when you are a child.

Thanks for this MOST interesting discussion. I am getting addicted to this site

Well yes synapses are slow. That is why I mentioned gap junction synapses and not regular chemical synapses

Yep certainly, gap junctions are as fast, if not faster than neuronal connections

in a gap junction synapse the membranes are connected, so AP can flow into the next cell. But the distension of the cell at the soma may slow down the signal

Ah, I didn't know that

I thought it was pretty much passive electric conduction, like putting an electrode in saline

but then signal can be amplified by the soma.. Damn this is an interesting thing to think about

Absolutely. Signal amplification is the reason of the existence of the internodes in the myelin sheath, It slows down the propagation, but boosts the signal back to base line

Nice to be able to use damn and fucked up when away from the site proper eh?

So now the question is.. What is the advantage of having a single axon that long. Has this been asked here?

yeah :D

Well the advantage, as we agreed upon I guess, is preventing synaptic delays. at the cost of vulnerability.

If you post the question and answer yourself, that gives one a badge isn't it ;)

But yes, I think it is an excellent question!

brb

coffee time

Sure. have to get working myself.

hehe enjoy!

Hi

hey

what do you think?

playing around with chats? :-)

yep.. This question is interesting.. I am planning to ask it

and link the chatroom for speculations

and discussion

go for it

i would say

seems an interesting problem

whats your take

chris stronks can clearly anwer it :-)

room topic changed to Long axons vs serial neurons: Imported from a comment discussion on biology.stackexchange.com/questions/21137/… [action-potential] [neuroscience]

@GriffinEvo if you have some time then post your comment about this.

I want to know if there is any work on this. Or this is a decent problem to model

I'm not sure what I can offer on the subject

evolutionary perspective :)

could you summarise to catch me up on the issue?

imagine a long neuron. The nucleus is overburdened.

any small dysfunction could impair the communication channel.

the physiological question is if there is any advantage, signal-response wise for having such a long neuron

but there can be another question too: why did this not get selected against

1m long cell with just one nucleus is a bit hard to imagine.

The questions I would say then are from an adaptive point of view: Do 10 x 10cm neurons work as well as, better, or worse (speed, accuracy, durability?) than a 1x100cm long one? And which would be more complex to evolve? ...

if the two work equally well then one might expect that these would be simply two different evolutionary trajectories (one long or many short) for the same result

thinking about the progression of the adaptation I'd guess the elongation would be more likely because neurones have variation in their length thus the machinery to make variable lengths exists, and elongation of the limbs (requiring elongation of the neurons) is gradual - feels like the multiple neurons route would have some weird points where one neuron is too short and two is too long...

So if there is no mechanistic advantage I'd suggest the advantage to elongating one neuron over developing many is the simplicity of doing it

whyevolutionistrue.wordpress.com/2011/05/28/…

towards the bottom.. "Wedel points out that cells this long pose some obvious problems to the physiologist:...."

BTW, what do the three of you do? @WYSIWYG @ChrisStronks @Chris

@GriffinEvo I am a PhD student.. 5th year.. 1st year was coursework.. 3 years I worked on experimental synthetic biology.. 3 projects- all failed

now I am doing mathematical modeling

wrt to having single long cell.. why is it simple.. To maintain such a long cell is a burden isnt it. It seems better to have multiple nuclei- there would be a limit to that also.

its a common route in to theoretical biology :)

haha.. depends .. for a biologist perhaps it is the common route

I wish to learn more mathematics

information theory really interests me..

RE long cells, I don't know enough about to even be able to make guesses, the above is just my gut feeling of it.

I am thinking of modeling this problem.. some avenue for a paper too... Talked to a friend who works on neurological models

I am currently having to work on my maths, having not done math since high school (and having not bothered all that much while I was there) I now find myself trying to comprehend matrix structure, multidimensional space, and eigendecomposition

Where is this phd you're doing? - US I guess if you are already 5 years in!

i attended a lecture recently.. though I understand a little math someone showed an equation about population dynamics.. I didn't know what carrying capacity is.. went back, read and then got the point. He was showing the logistic growth equation and I was asking why is there a second order death term.. Terminologies are also a problem

no I am in India

definitely

where are you working ?

Uppsala in Sweden... little colder than India!

Yeah.. you told.. my bad.. well much colder than average India.. :P

I like winters better

But I'm British (ps can we not talk about cricket, normally I'd be happy to but things aren't so good for us right now)

ahh.. I am not a great cricket enthusiast.. we can talk about English language perhaps :P

@GriffinEvo what is your thesis basically? 3rd year you are ?

The evolution of sex differences in complex traits - in my fourth (and final) year now

I use hemiclones, a really exciting method using good ol' fruit flies, and quantitative genetic analyses to test the constraint of a shared genome on the evolution of sexual dimorphism

...exciting as in novel and powerful, a scientific excitement - but not literally exciting to use everyday ;)

Hemiclones.. I had not heard of that term.. can you give a small intro.. googling directs me to papers..

and well.. I am not a fan of doing things that have immediate benefit.. I shamelessly confess that my sole motivation is to learn more and nothing else.. humanity will somehow keep itself alive.. it is not going to perish in our lifetime; so I am not bothered to do something for it

it means we can make every fly within a line share exactly one copy of each chromosome, while the other half of the genome varies randomly both within and between lines - each line can be sampled infinitely...

well.. it takes a week to get a generation of flies right

yeah

ahhh.. careful and meticulous breeding

The reason that is exciting is two part: because classical methods such as sibling analysis are weakened by small sampling (limited by how many offspring each line-parent can produce before they die), and because in siblings the individuals share an average of 1/2 of the chromosomes but could be anywhere between none and all while we know every fly does share the exact same component

yes this is technique would demand great attention and bookkeeping

the actual lab work is as intense as classical methods - at most (I can maintain lines indefinitely and repeatedly assay traits over many blocks) so I can even do experiments by many small blocks

I have a doubt here. DO you fix which chromosome you want to hold constant

I mean which half of the genome

what about the crossovers and all?

forgive me for my ignorance

no recombination in males so we keep the focal half maintained in a male where the opposing member of each chromosome pair is marked with recessive and dominant markers, that way we can mate them every 6-8 weeks (to another special type of fly) and track the focal chromosomes

"A hemiclone is equivalent to the offspring that would be produced by randomly picking a group of eggs from the base population and then fertilizing each egg with a cloned copy of the same sperm."

this demands more work than the sibling methods I guess

that's just an analogy, it's all done with basic crosses (I mix some yellow bodied white eyed females with some brown eyed males and collect the brown eyed sons to maintain lines)

If you ask the question on bio se "What is a hemiclone I can answer it - including the diagrams to show construction :)

;P

I just read it...

I prefer not to ask things that I can find..

:P

haha

and perhaps get to know over a conversation

but you can paste a link about it

i cant find a good link

asking it might be decent..

this one is a fairly good overview of it jessicakabbott.com/documents/…

Perhaps I should create another room for our conversation

yeah, I/we somewhat diverted this!

Hi! sad to see this discussion leave the room. Can I join into the new discussion again? (Still learning :-)

Anyway: @GriffinEvo : So you are a British PhD student working in Uppsula on evolutionary genetics? Classy workplace you have :)

I am a postdoc in Canberra where I work on sensory substitution. Sensory substitution is a way to replace a lost sense by re-directing information to another functional sense. In short, we want to let blind folks 'see with their skin'. I have been working on retinal implants previously in the US, and cochlear implants for my PhD in the Netherlands. I am Dutch.

I read @WYSIWYG 's response: 5th year PhD on mathematical modeling? Are you able to use those 'failed' studies for your thesis? I hope so for you. Good luck!

@Chris - I am very curious to your backgrounds :)