[extropy-chat] Neuro links

[Alex Ramonsky]

Hello!
The synaptic cleft (the actual 'gap' bit of the gap) is about 10 to 20 
nm across. (The synaptic 'gap' is the space between and the membranes 
both sides, so about 20-30nm) A single vesicle full of neurotransmitter 
is about 50nm in diameter, and fits at least 10,000 molecules of 
transmitter inside. It has to really move its ass and if the gap were 
any bigger, we'd probably all have been eaten waiting for the fight 
flight response to happen  :  )
Diameter of neurons varies from  4 micron (granule cell) to 100 micron 
(motor neuron in cord)
(Diameter of neuron nucleus = 3 to 18 micron).
The plasma membrane itself is about 5nm.
Diameter of microtubule = 20-25 nm
Diameter of neurofilament = 7-10 nm
...But the density of neurons is an individual thing, and will vary from 
area to area in each individual, and throughout that individual's 
lifetime. An individual who regularly uses all bits of the brain a lot 
will really pack 'em in, especially in bits like the hippocampus. 
Einstein's looked like someone had tried to shove far too much macaroni 
into a very small pot.
So if you want more elbow room for your bots, choose an extraordinarily 
stupid subject, preferably with dendritic shrinkage already, big 
ventricles and a small hippo.
...Like, almost any celebrity?  :  )
Otherwise, why not consider designs that are long and thin? Things that 
could go UP axons ...Nanoworms. (Cue for a bad sci fi movie where 
nanoworms infest everyone's brains and the hero invents the first 
intrathecal anthelmintic, but cannot tell anybody because you cannot 
pronounce that over the telephone).
...Please accept my apologies; I have been awake for a very long time.
I'll stop now.
Best,
AR
*********************
Brett Paatsch wrote:

> Hi Alex,
>  
> Do you know how much space is between axons, dendrites, synapses on 
> neurons in the most densely packed part of the brain? ie how tight do 
> neurons pack at
> their tightest and most dense?
>  
> Reason I ask is that I think that is an important design scale 
> limit on any servicing/repairing nanobots that might want to get 
> between them.
>  
> In actual fact I suspect that to try and get a nanobot into the 
> extracellular spaces between neurons may be impossible, because 
> the space may be
> as little as 10s of nanometres in places (and the space map would be 
> different for every brain - more different than variations in 
> vasculature) and
> no nanobot with a payload worth a damn could get much smaller than a 
> half a micron I'd guessimate.
>  
> Cheers,
> Brett
>  


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