made in/ of

it is a somewhat widespread belief that every cell in the human body is replaced in a seven year cycle; that every seven years (or ten, depending on where you get the story) we are basically new people. this belief, even if not entirely accurate, is not entirely faulty, either; it is true that every cell type has their own life span, and once a cell dies it is replaced - only the process is constant and doesn't have an exact start or end.

when you think about it, it does give one a sense of renewal; if the cells you drag around as your body aren't the same ones you were born with, doesn't it make you feel.. newer? doesn't it make you think you can start again, treat your body better? doesn't it give you a feeling that starting again is really physically possible?

however, not all the cells in our body are replaced. the ones to break this cycle of renewal are the neurons in your cerebral cortex, the number of which doesn't increase after birth; which also means that cerebral cortex neurons are not replaced when they die. another group to regenerate very slowly are the cardiomyocyte heart cells as they are replaced at a slow rate that only reduces the older we get; a person of old age has had approximately less than half of his or her cardiomyocyte cells replaced, and those that haven't been replaced have been there since birth.

so what stays - our head and our heart. it's a simplified thought but in its naivety almost endearing. but what makes it and the thought that perhaps follows - that maybe here could hide some kind of clue into our consciousness, into our sense of self and concept of existence - truly fascinating is the application of the fact that your atoms are not yours, that energy is in constant movement. 

or, as steve grand has said it:

"Think of an experience from your childhood. Something you remember clearly, something you can see, feel, maybe even smell, as if you were really there. After all, you really were there at the time, weren’t you? How else would you remember it?

But here is the bombshell: you weren’t there.

Not a single atom that is in your body today was there when that event took place … Matter flows from place to place and momentarily comes together to be you.

Whatever you are, therefore, you are not the stuff of which you are made.

If that doesn’t make the hair stand up on the back of your neck, read it again until it does, because it is important."

and it is. it really is. even if i don't quite know what it means.