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> miles of nerves?
dfilms
post Oct 10, 2007, 12:57 PM
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Hi Guys,

I am doing some research into the nervous system for a documentary I working on. I have read everywhere on the net that humans have roughly "45 miles of nerves" - is this actually true? If not, what is the right number?

I have also read that about 10% of our nervous system is dedicated solely to nociception or pain - does this sound accurate? Again, if not, what would be a better, more accurate number?

Any kind of help or guidance on this would be very much appreciated.

Thanks Again!

James
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lucid_dream
post Oct 10, 2007, 04:29 PM
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I've heard this same figure about 45 miles of nerves but have never found the source of this claim. It's probably a gross underestimate though. Here's a rough calculation: The human brain is about 10cmx10cmx10cm. About 40% of that is myelinated and unmyelinated axons, with each axon about 1 micron in diameter, which means there's about 10cm*((10cm/0.0001 cm)^2)*0.4 = 4x10^10 m. Since there are 1609.344 meters per mile, it works out to about 2.5x10^7 miles, or 25 million miles.

About the claim that 10% of the nervous system is dedicated to pain, there is no way currently to determine this. To say that it's because 10% of the brain lights up in fMRI when someone experiences pain would be incorrect, partly because activated areas could be involved with processing a motor response to the pain. Also, it's believed there are two components to pain; affective and sensation, with the former being in limbic areas and latter being in somatosensory areas. If you include these somatosensory areas, then the figure easily exceeds 10%.
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dfilms
post Oct 12, 2007, 03:39 AM
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QUOTE(lucid_dream @ Oct 10, 2007, 04:29 PM) *

I've heard this same figure about 45 miles of nerves but have never found the source of this claim. It's probably a gross underestimate though. Here's a rough calculation: The human brain is about 10cmx10cmx10cm. About 40% of that is myelinated and unmyelinated axons, with each axon about 1 micron in diameter, which means there's about 10cm*((10cm/0.0001 cm)^2)*0.4 = 4x10^10 m. Since there are 1609.344 meters per mile, it works out to about 2.5x10^7 miles, or 25 million miles.

About the claim that 10% of the nervous system is dedicated to pain, there is no way currently to determine this. To say that it's because 10% of the brain lights up in fMRI when someone experiences pain would be incorrect, partly because activated areas could be involved with processing a motor response to the pain. Also, it's believed there are two components to pain; affective and sensation, with the former being in limbic areas and latter being in somatosensory areas. If you include these somatosensory areas, then the figure easily exceeds 10%.


Thanks for this, very helpful...I have also read elsewhere that we have around:

7.4 million miles of dendrites
62000 miles of axons
3 million miles of axons

I guess "45 miles of nerves" is actually referring to nerve fibers, or bundles of axons, which would make more sense.

but which one to use...?




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