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

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...?