7 ms·

I have always had great difficulty in believing that in the human body, _everything_ is regularly regenerated with the exception of neurons/ganglia. The case i

I have always had great difficulty in believing that in the human body, _everything_ is regularly regenerated with the exception of neurons/ganglia. The case in point is the sciatic nerve is massive, and prone to constant stresses and strains, yet supposedly never regenerates.

screye 8y ago
Evolution is stupid. Evolution doesn't try to head towards any global optima, so it is quite believable that certain things just don't work a certain way even if they sound 'obvious' to rational beings.
- eanzenberg 8y ago
  Evolution: Requires a lot of things dying over a long period of time to get to where you are, today.
  - deleted 8y ago
    [deleted]
- godelski 8y ago
  > Evolution doesn't try to head towards any global optima If one even exists. I don't think you could actually say a global optima exists in a lot of cases. Since there are a lot of compounding factors and the functions aren't required to be continuous.
earenndil 8y ago
I thought nerves aren't regenerated either?
- wickedsmile 8y ago
  Intact I read somewhere Cannabis consumption results in Neurogenesis. I am trying to find something for citation but unable to find anything backing this claim
  - darkpuma 8y ago
    Cannabis's Schedule I status makes it difficult for legitimate researchers to debunk (or confirm) the ever growing volume of nonsense cannabis proponents put forward to support legalization. Which ironically, is a pretty good argument for rescheduling it at least.
  - meko 8y ago
    Claims of legitimacy aside, The CBD portion of cannabis is supposed to have this affect, not thc.
    - heavenlyblue 8y ago
      Why CBD specifically? Where do you get that data?
- magduf 8y ago
  They certainly do. From a very quick google search: https://www.sciencedaily.com/releases/2010/09/100927141144.htm https://www.sciencedaily.com/releases/2010/09/100927141144.h...
- ergothus 8y ago
  It was thought so for a while, but recently (~10-20 years) was discovered that they do, albeit slowly.
- adrianmonk 8y ago
  They are sometimes. One of mine did. I had some nerve damage a while back and went to a neurologist. He did an EMG test (https://en.wikipedia.org/wiki/Electromyography https://en.wikipedia.org/wiki/Electromyography) and confirmed the nerve was damaged. He used electrodes to show that it did not conduct electricity like it was supposed to, nor did it conduct electricity like the corresponding one on the other side of my body. (Somewhere, I have a printout showing voltage and latency numbers.) He then told me that if the damage is not too great, nerves can repair themselves, that the repair proceeds outward from the brain toward the periphery of the body, and that it happens at a rate of roughly 1 millimeter per day. So, he said, my problem would probably resolve itself but it would be a long time, think 6 months or a year, maybe even longer to finally be back to 100%. And it basically happened just like he said it would. 6 months later, it was a lot better, and it continued to gradually improve from there. He also mentioned that using the affected muscles would help encourage healing. I think he meant the nerve itself would heal faster this way, not just that it would help reverse muscle atrophy.
  - holoduke 8y ago
    So instead of growing back the missing /damaged nerve, an entire new nerve string grew from the brains back to the original nerve? Didn't know that
    - adrianmonk 8y ago
      My layman's understanding is that a nerve is kind of a bundle of fibers wrapped in an outer layer. (Perhaps it's reasonable to compare it to a stranded wire inside an insulator, though I wouldn't say for sure.) He said that if the outer layer is intact, the inner layer can be repaired. I'm not sure if that means more nerve fibers form or that existing nerve fibers are repaired but that the repair takes place incrementally instead of all at once. Intuitively it seems to make sense that a new fiber is growing, but I'm wary of speculating based on what seems to make sense to me.
- redcalx 8y ago
  I cut a nerve at the base of my middle finger one time and completely lost feeling. Feeling came back over two or three weeks as the cut healed and eventually came back 100%.
- m00x 8y ago
  Peripheral nerves are well known to regenerate, but the spinal nerves do not (or very limited). We do not want nerves to regenerate in most cases because it could cause even worse results. If you start regrowing a batch of nerve, you have a chance of growing out nerves that transfer pain signals into places you don't want them to be, which could cause persistent neuropathic pain (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5290455/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5290455/).
newnewpdro 8y ago
Same here, and it always seemed obvious to me that the brain was regenerating considering the nearly constant barrage of destructive shit thrown at it in adulthood without becoming vegetative; alcohol.
abainbridge 8y ago
I believe the cells in your eye's lens are not replaced. New cells are added around the outside but the old ones are never taken away / broken down. This is why our lenses become cloudy and more rigid in old age.
- kypro 8y ago
  Same with the heart too, I believe. It isn't able to create new muscle cells in adulthood.
  - KaiserPro 8y ago
    I think we can simply demonstration that the heart does regenerate. 1) looking at people before and after 1 month of regular exercise. 2) healing of heart after large and invasive surgery.
    - abainbridge 8y ago
      That is a compelling argument. But, if you Google for "heart cells don't regenerate", you find that it does appear to be a thing experts believe. And you find article like this that attempts to explain why heart cells can't regenerate: https://www.sciencedaily.com/releases/2011/08/110809092102.htm https://www.sciencedaily.com/releases/2011/08/110809092102.h...
chongli 8y ago
The case in point is the sciatic nerve is massive, and prone to constant stresses and strains, yet supposedly never regenerates. Sciatica doesn't generally show up until people are in their 40s-50s. This is long after childbearing years for most people. At that point your sciatic nerve has done its job and gotten you across the finish line. What happens next is less important.
- jimmaswell 8y ago
  Less important but your fitness is still relevant in terms of survival of the tribe, which is selected for since it affects the survival of any one individual.
  - TomMarius 8y ago
    Were there tribe members that lived in their 50s? I thought it was common to die before 40s.
    - anoncake 8y ago
      Low life expectancies in the past were mostly due to high child mortality.
      - TomMarius 8y ago
        I know that and have accounted for that. I'm talking about prehistoric times, when we were developing.
        pickpuck 8y ago
        Based on the data from modern hunter-gatherer populations, it is estimated that at 15, life expectancy was an additional 39 years (total 54), with a 0.60 probability of reaching 15. https://en.m.wikipedia.org/wiki/Life_expectancy https://en.m.wikipedia.org/wiki/Life_expectancy
    - saiya-jin 8y ago
taneq 8y ago
And teeth. And corneas. There are quite a few things that only last long enough to get you sufficiently past child bearing age. Of course, old people can learn new things so I always thought the "neurons don't grow" thing was silly (although I guess it's possible that we have a set number of neurons and it's just our synapses that keep growing).
- KaiserPro 8y ago
  Hmm, Teeth do regenerate, but only at a certain rate, hence holes and stuff. Those people who loose saliva production end up loosing teeth as well, because the enamel disappears. I have no idea about corneas.
  - taneq 8y ago
    Do teeth regenerate? A quick search for 'tooth enamel regeneration' turns up a bunch of pages saying it can't regenerate, and a couple about some researchers who found some treatment which does let it regenerate somewhat. I hope you're right, though.
m00x 8y ago
We're built to just last long enough to procreate because that's been the optimal way to keep our species alive. Regenerating causes issues (cancer, malformations, takes energy), so if the body can build it only once and last 20-30 years, it's optimal.
agumonkey 8y ago
Some studies on the .. axolotl ? (limb regrowing salamanders) showed that human had similar capabilities BUT with a very fast bailout mechanism that stopped the regeneration a lot earlier.
WhiteSage 8y ago
Auditory hair cells in the inner ear -the ones that allow us to hear sound- do regenerate in many animals but this mechanism fails in mammals. The surrounding cells try to replace them but something goes wrong and they die. This is why hearing loss is permanent, and exemplifies how stupid evolution can be at times.
- saiya-jin 8y ago
  Evolution, AFAIK is just a random mutations happening here and there. If they bring some advantage (which good hearing in later age definitely should, but then again it covers mostly later age), harshness of life should eventually select those individuals as better survivalists. Apparently whatever mutation happened in the past in this regard was not good enough / human still didn't survive, or it didn't happen yet. It might be funny if we discover some remote tribe actually has this regenerative mutation. I think its question of time (maybe very long time), look at our unique ability to process lactose in adult age.
  - close04 8y ago
    Anything that happens after the end of an individual’s reproductive years (perhaps also the period of raising the offsprings) stops exerting any evolutionary pressure. The fact that you have a “defect” at old age no longer blocks you from transmitting it so it can propagate through generations without evolution selecting against it. Random mutations “fixing” the gene can occur but still have to compete with the overwhelming number of non mutated “defective” genes.
    - 7j 8y ago
      > Anything that happens after the end of an individual’s reproductive years (perhaps also the period of raising the offsprings) stops exerting any evolutionary pressure. This is definitely wrong. Individuals (e.g. grandparents or just random society members) can influence survival rates of other society members. Some species(e.g. ants) even have sterile members that definitely exert evolutionary pressure.

screye 8y ago

Evolution is stupid. Evolution doesn't try to head towards any global optima, so it is quite believable that certain things just don't work a certain way even if they sound 'obvious' to rational beings.

eanzenberg 8y ago
Evolution: Requires a lot of things dying over a long period of time to get to where you are, today.
- deleted 8y ago
  [deleted]
godelski 8y ago
> Evolution doesn't try to head towards any global optima If one even exists. I don't think you could actually say a global optima exists in a lot of cases. Since there are a lot of compounding factors and the functions aren't required to be continuous.

earenndil 8y ago

I thought nerves aren't regenerated either?

wickedsmile 8y ago
Intact I read somewhere Cannabis consumption results in Neurogenesis. I am trying to find something for citation but unable to find anything backing this claim
- darkpuma 8y ago
  Cannabis's Schedule I status makes it difficult for legitimate researchers to debunk (or confirm) the ever growing volume of nonsense cannabis proponents put forward to support legalization. Which ironically, is a pretty good argument for rescheduling it at least.
- meko 8y ago
  Claims of legitimacy aside, The CBD portion of cannabis is supposed to have this affect, not thc.
  - heavenlyblue 8y ago
    Why CBD specifically? Where do you get that data?
magduf 8y ago
They certainly do. From a very quick google search: https://www.sciencedaily.com/releases/2010/09/100927141144.htm https://www.sciencedaily.com/releases/2010/09/100927141144.h...
ergothus 8y ago
It was thought so for a while, but recently (~10-20 years) was discovered that they do, albeit slowly.
adrianmonk 8y ago
They are sometimes. One of mine did. I had some nerve damage a while back and went to a neurologist. He did an EMG test (https://en.wikipedia.org/wiki/Electromyography https://en.wikipedia.org/wiki/Electromyography) and confirmed the nerve was damaged. He used electrodes to show that it did not conduct electricity like it was supposed to, nor did it conduct electricity like the corresponding one on the other side of my body. (Somewhere, I have a printout showing voltage and latency numbers.) He then told me that if the damage is not too great, nerves can repair themselves, that the repair proceeds outward from the brain toward the periphery of the body, and that it happens at a rate of roughly 1 millimeter per day. So, he said, my problem would probably resolve itself but it would be a long time, think 6 months or a year, maybe even longer to finally be back to 100%. And it basically happened just like he said it would. 6 months later, it was a lot better, and it continued to gradually improve from there. He also mentioned that using the affected muscles would help encourage healing. I think he meant the nerve itself would heal faster this way, not just that it would help reverse muscle atrophy.
- holoduke 8y ago
  So instead of growing back the missing /damaged nerve, an entire new nerve string grew from the brains back to the original nerve? Didn't know that
  - adrianmonk 8y ago
    My layman's understanding is that a nerve is kind of a bundle of fibers wrapped in an outer layer. (Perhaps it's reasonable to compare it to a stranded wire inside an insulator, though I wouldn't say for sure.) He said that if the outer layer is intact, the inner layer can be repaired. I'm not sure if that means more nerve fibers form or that existing nerve fibers are repaired but that the repair takes place incrementally instead of all at once. Intuitively it seems to make sense that a new fiber is growing, but I'm wary of speculating based on what seems to make sense to me.
redcalx 8y ago
I cut a nerve at the base of my middle finger one time and completely lost feeling. Feeling came back over two or three weeks as the cut healed and eventually came back 100%.
m00x 8y ago
Peripheral nerves are well known to regenerate, but the spinal nerves do not (or very limited). We do not want nerves to regenerate in most cases because it could cause even worse results. If you start regrowing a batch of nerve, you have a chance of growing out nerves that transfer pain signals into places you don't want them to be, which could cause persistent neuropathic pain (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5290455/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5290455/).

newnewpdro 8y ago

Same here, and it always seemed obvious to me that the brain was regenerating considering the nearly constant barrage of destructive shit thrown at it in adulthood without becoming vegetative; alcohol.

abainbridge 8y ago

I believe the cells in your eye's lens are not replaced. New cells are added around the outside but the old ones are never taken away / broken down. This is why our lenses become cloudy and more rigid in old age.

kypro 8y ago
Same with the heart too, I believe. It isn't able to create new muscle cells in adulthood.
- KaiserPro 8y ago
  I think we can simply demonstration that the heart does regenerate. 1) looking at people before and after 1 month of regular exercise. 2) healing of heart after large and invasive surgery.
  - abainbridge 8y ago
    That is a compelling argument. But, if you Google for "heart cells don't regenerate", you find that it does appear to be a thing experts believe. And you find article like this that attempts to explain why heart cells can't regenerate: https://www.sciencedaily.com/releases/2011/08/110809092102.htm https://www.sciencedaily.com/releases/2011/08/110809092102.h...

chongli 8y ago

The case in point is the sciatic nerve is massive, and prone to constant stresses and strains, yet supposedly never regenerates. Sciatica doesn't generally show up until people are in their 40s-50s. This is long after childbearing years for most people. At that point your sciatic nerve has done its job and gotten you across the finish line. What happens next is less important.

jimmaswell 8y ago
Less important but your fitness is still relevant in terms of survival of the tribe, which is selected for since it affects the survival of any one individual.
- TomMarius 8y ago
  Were there tribe members that lived in their 50s? I thought it was common to die before 40s.
  - anoncake 8y ago
    Low life expectancies in the past were mostly due to high child mortality.
    - TomMarius 8y ago
      I know that and have accounted for that. I'm talking about prehistoric times, when we were developing.
      - pickpuck 8y ago
        Based on the data from modern hunter-gatherer populations, it is estimated that at 15, life expectancy was an additional 39 years (total 54), with a 0.60 probability of reaching 15. https://en.m.wikipedia.org/wiki/Life_expectancy https://en.m.wikipedia.org/wiki/Life_expectancy
  - saiya-jin 8y ago

taneq 8y ago

And teeth. And corneas. There are quite a few things that only last long enough to get you sufficiently past child bearing age. Of course, old people can learn new things so I always thought the "neurons don't grow" thing was silly (although I guess it's possible that we have a set number of neurons and it's just our synapses that keep growing).

KaiserPro 8y ago
Hmm, Teeth do regenerate, but only at a certain rate, hence holes and stuff. Those people who loose saliva production end up loosing teeth as well, because the enamel disappears. I have no idea about corneas.
- taneq 8y ago
  Do teeth regenerate? A quick search for 'tooth enamel regeneration' turns up a bunch of pages saying it can't regenerate, and a couple about some researchers who found some treatment which does let it regenerate somewhat. I hope you're right, though.

m00x 8y ago

We're built to just last long enough to procreate because that's been the optimal way to keep our species alive. Regenerating causes issues (cancer, malformations, takes energy), so if the body can build it only once and last 20-30 years, it's optimal.

agumonkey 8y ago

Some studies on the .. axolotl ? (limb regrowing salamanders) showed that human had similar capabilities BUT with a very fast bailout mechanism that stopped the regeneration a lot earlier.

WhiteSage 8y ago

Auditory hair cells in the inner ear -the ones that allow us to hear sound- do regenerate in many animals but this mechanism fails in mammals. The surrounding cells try to replace them but something goes wrong and they die. This is why hearing loss is permanent, and exemplifies how stupid evolution can be at times.

saiya-jin 8y ago
Evolution, AFAIK is just a random mutations happening here and there. If they bring some advantage (which good hearing in later age definitely should, but then again it covers mostly later age), harshness of life should eventually select those individuals as better survivalists. Apparently whatever mutation happened in the past in this regard was not good enough / human still didn't survive, or it didn't happen yet. It might be funny if we discover some remote tribe actually has this regenerative mutation. I think its question of time (maybe very long time), look at our unique ability to process lactose in adult age.
- close04 8y ago
  Anything that happens after the end of an individual’s reproductive years (perhaps also the period of raising the offsprings) stops exerting any evolutionary pressure. The fact that you have a “defect” at old age no longer blocks you from transmitting it so it can propagate through generations without evolution selecting against it. Random mutations “fixing” the gene can occur but still have to compete with the overwhelming number of non mutated “defective” genes.
  - 7j 8y ago
    > Anything that happens after the end of an individual’s reproductive years (perhaps also the period of raising the offsprings) stops exerting any evolutionary pressure. This is definitely wrong. Individuals (e.g. grandparents or just random society members) can influence survival rates of other society members. Some species(e.g. ants) even have sterile members that definitely exert evolutionary pressure.