Thread: Neuron Replacement & a Troubling Thought

I know that different cells in your body replace at varying rates. And I could have sworn that in one of my biology courses I was taught that neurons are the only cells that do not replace themselves throughout your life. This was pleasing to me because otherwise my older self would essentially be a different being than my younger self.

However, I recently saw a youtube video that I thought came from a fairly legit source which claims that all cells are eventually replaced and that you will actually have none of the same atoms you were born with...anyone know if this is true?

The youtube video is from AsapScience and is called "Amazing Facts to Blow your Mind Pt. 1". The comments referenced are at about the 1:00 mark.

If neurons do replace, it suggests the notion that long-term planning is just planning for some other person does it not?

Originally Posted by markashley

And I could have sworn that in one of my biology courses I was taught that neurons are the only cells that do not replace themselves throughout your life.

Your biology instruction was correct. Neurons do not get replaced. You have the same neurons from birth, til death, excluding the ones that die.
However... neurons can and will expand their productivity, so while you won't grow new ones, you can develop more efficient ones. In addition to this, glial cells do reproduce and contribute to information processing within the brain. This bit of information pertains to several points below...

Originally Posted by markashley

This was pleasing to me because otherwise my older self would essentially be a different being than my younger self.

Bad news on this bit, however... You are a different person than you were ten years ago.
And in twenty years you will be a different person from today.

But maybe this bit will make it easier... You're also a different person than you were five minutes ago... This topic would best be left for a whole new thread

Originally Posted by markashley

However, I recently saw a youtube video that I thought came from a fairly legit source which claims that all cells are eventually replaced and that you will actually have none of the same atoms you were born with...anyone know if this is true?

It is untrue.
And neurons are not the only ones- Many of your heart muscles do not replace as well. Some do, some don't. You will die with many of the heart muscles you had at birth. The heart muscle cells grow in size, instead, and are very slow to reproduce.

Originally Posted by markashley

it suggests the notion that long-term planning is just planning for some other person does it not?

Yes, but not because neurons are replaced- but because their functionality changes with development. Don't worry about it too much- you'll hardly ever know the difference. Well, not much. Not usually anyway- barring catastrophic changes to your brain.

Not at all. The same thing goes for planting a garden. You start with seeds or seedlings or saplings. You actively feed and water them or you chose them so that the soil and seasonal conditions will do it for you. Most importantly you prune out dangerous or diseased portions to promote healthy growth of individual plants or of whole garden sections. Some plants crowd or shade out others, so you remove them or raise the canopy or prune them selectively to allow better overall growth of the garden as a whole. If you're trying to encourage certain birds or insects you promote or reduce the number or size of particular plant habitats and food sources for those critters.

The mature 20 year old garden is nothing like the original planting.

That's what happens with neurons and their connections. The huge growth in infancy and early childhood is adjusted, refined and pruned, severely, during adolescence so that the adult brain is very, very different from any stage of growth of the brain up to that point.

Similar processes apply both to the development from infancy to adulthood of the rest of the body and also to maintenance of the condition of the adult body. Think about the sexual organs and features of the body for starters. These are controlled by some hormones generated by organs not obviously related to sex, the thyroid?, the brain?, and linked to other functions of other body parts apparently just as unrelated to sexual functioning.

Since this is Biology you should always be prepared to be hit with exceptions to the rule. While damaged neurons of the CNS typically don't regenerate, some of them can be replaced from stem cell precursors. In other words: new neurons are created in the brain, and what you had at birth is not really the same as that you have now.

Originally Posted by Zwirko

Since this is Biology you should always be prepared to be hit with exceptions to the rule. While damaged neurons of the CNS typically don't regenerate, some of them can be replaced from stem cell precursors. In other words: new neurons are created in the brain, and what you had at birth is not really the same as that you have now.

You might need to clarify this because your statement implies a totality (And I did the same thing referring to the heart muscle above which needs correcting but I may not bother now since I've directed attention to it here...)
Rather, you might say that some neurons do get replaced, but as the first sentence- are exceptions, not the rule. So what he will have at death will be a few new neurons that he was not born with.
Also, can you clarify where the stem cell precursors come from and how often they are used?

The Wikipedia article on neurogenesis probably answers most of those questions. Neurogenesis - Wikipedia, the free encyclopedia

I'm pretty sure the way I phrased it first time round was just fine

Originally Posted by Zwirko

I'm pretty sure the way I phrased it first time round was just fine

Are you saying that all of the neurons are then replaced and that at death, you do not have the neurons you were born with?

Nope.

Just pointing out that there are some exceptions here and there. So instead of saying neurogenesis is non-existent in the adult brain, we would be better off saying that it is largely absent, and observed to occur only in some specific regions of the brain.

Good deal- thanks for the clarification and the correction to what I had said.

Neurons do form and regenerate through out your life. Think if neurons don't regenerate or new neurons don't come up then how will you learn or form memory of some thing. Four to five decades before this idea of non-plastic nervous system prevailed a lot however some clever experiments have totally eradicated this idea. You can check the 'The phantom limb' experiment by Dr. V. S. Ramamchandran. However now there are many such experiments which have proven the plasticity of nervous system.

Neuralplasticity and neurogenesis, although having an area of overlap, are two separate things. Neuralplasticity largely deals with changes in synapses and neural pathways as a response to things like environmental input, learning or injury. So yes, the brain is not the static structure it was once believed to be. Neurogenesis, on the other hand is about the creation of new neurons. So far it has only been observed, after great difficulty, in a few areas of the brain.

The phantom limb experiments are examples of neuralplasticity, not examples of neurogenesis.

As far as I remember the phantom limb experiment is still under debate whether its is a neural plasticity or neurogenesis. However plasticity in nervous system can arise due to changes in the synapses as well as by formation of new neurons. So it depends upon the context you are talking about. As far as the initial question of this post, I think we both agree on this point that surely the nervous system is not static.