What’s the dope on our bodies regenerating every year? I find it cool that we have regenerated a whole new body in a year. Is this true? If so, how do we remember things if our brain tissue regenerates?
Its an urban legend.
actually it was (is?) thought that the brain does not regerate new cells, but we are stuck with them. No new brain cells for you – settling the neurogenesis debate | Not Exactly Rocket Science I vaguely recall that may not always be true and some new research may indicate some repair etc but I cant find it offhand
I don’t think it is quite an urban legend, but it is true that most of our bodies are replaced regularly. Red blood cells for instance are replaced every 30 days, skin cells are replaced, muscle cells (mostly glycogen and water) are replaced simply through attrition, and skeletal mass in adults is completely replaced every 10 to 15 years.
The year thing could just be a corruption of these facts.
They do in the Hippocampus.
If that were true, tattoos would only last a year.
Why? I don’t see any reason for that.
You think the ink makes it’s way into your DNA? If the cells all die off and are replaced, then the new replacement cells wouldn’t have the ink. Tattoos fade over time, but don’t just “disappear” which seems to indicate that not all the cells in your body are “replaced”
Hi all. I wrote the article in scm1001’s link. As I understand it, both he and Epimethius are right. The only places in the brain that naturally produce new nerve cells are the hippocampus (involved in spatial awareness, memory etc.) and the olfactory bulb (involved in smell). Other parts of the brain including the neocortex (the bit that controls our higher mental abilities) don’t create new nerve cells after we’re born. We’re stuck with the same ones that just make new connections with each other in order to deal with new experiences and memories.
I think the situation with tattoos is that your skin is constantly replaced, but only the top layer. The ink in tattoos makes its way down to the base layers of the skin which are not nearly so frequently replaced, which is why they’re permanent.
Tattoos aren’t part of your body. They are made of ink injected into the skin. The skin cells around the ink are replaced, the ink itself just sits there. At least that is how I understand it.
you may be right
“The tattoo pigment is not within the cells, but in the space between them,” adds Dr. Nachbar, “So replacing the cells doesn’t help.”
wonderquest.com
In the above link by scm1001, it also says that the body’s cells that normally would ferry particles out of the skin are foiled by the ink molecules being too large to dispose of.
Wouldn’t it be great to see a time-lapse movie of that happening? Busy skin cells shedding away, with the tattoo in stasis.
This is so much why I like the SD; a good question, with an answer that seems logical (tattoos), and then disproved with an answer that isn’t what you’d easily think of.
And, welcome, Ed Yong. Nice of you to reply here. I find it interesting that the hippocampus is so centrally located and well-protected within the brain. In your post, though not in the linked article, you mention that the olfactory bulb also produces new cells. Sense of smell is key in most animals as a way to navigate the world, but has become remiss in humans. What’s the theory behind olfactory regeneration?
Welcome, Ed Yong. Thanks for your contributions, here and in the linked article. I personally hope you hang around here awhile and join in some of the lively discussions.
QtM
Does the actual structure of a cell not get recycled? Once a cell membrane is made, is it not in a constant state of regeneration. What about for ribosomes etc. If so, then a cell doesn’t have to die and be replaced for our bodies to be recycled. Even if nerve cells last our entire lives, that doesn’t necessarily mean the molecules in the cells aren’t replaced.
Look at the experiment given in scm1001’s link.
If the levels of Carbon 14 are set at birth then the molecules that contain the carbon must be the same molecules throughout. If the molecules changed, then they would have different levels of Carbon 14 from whatever time the change took place.
This implies that the neurons are fixed in their entirety.
Ahem.
I forget the name of the magazine, but about a year ago I read an article on neurogenesis. What struck me: The idea of adult humans not having neurogenesis entered the conventional wisdom & was embraced so utterly by educated society, generally without looking at or understanding the experimental data–even though all the other cells in your body have a mechanism of replacement; even though neurogenesis was shown by research to take place in at least some other animals. However, the experimental data amounted to a count of cells in the dead brains of non-human animals killed at different points in their lives.
The simplest explanation is best. All cell types have a mechanism of replacement. The brain is shown to develop knowledge, memory, &–whatever term the neurologists use for habituation. Ergo, neurogenesis can be presumed to happen.
Oh, & as mentioned above, some cells are replaced faster than others. So not everything in a single year, no.
Erm… neither of those links actually contradict anything I say in my post or article. Neurogenesis does take place in the hippocampus and olfactory bulb, but it would seem that it does only in those areas.
Obviously we develop knowledge, memory etc, and while we might naturally assume that this means we develop new brain cells, I think the picture emerging from current studies is that this is wrong. New knowledge and memories are encoded into the brain when the existing nerve cells form new connections with each other. Or to put it another way, it’s not how many neurons you have, it’s what you do with them that counts 
Hello!
I don’t really know the answer to the olfactory regeneration question. Maybe it’s a sort of evolutionary throwback? Smell, as you say, is a key sense in many other animals, and mammals in particular. Maybe this regeneration is important in other mammals and was never lost in primates?
I’m just speculating.
And of course the stomach replaces itself a lot faster again!
Inside the cells the individual componants do damge one another and constant repair is needed, atleast thats what it said in this book