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Comment by pknomad | Hacker News Reader

Unfortunate nomenclature aside, this issue highlights the difference between models and reality in science and how students can take these models too literally and thus easily conflate the two in pedagogy. Here's an embarrassing story for me: I didn't realize (or at least didn't internalize) that not all cells in the human body conform to to the canonical image of the cell that we see in Biology textbooks (https://en.wikipedia.org/wiki/Cell_(biology)#/media/File:Cel...) until I finished oncology and embryology class in my senior year back in 2015. For example, erythrocytes (RBCs) don't have nucleus and mitochondria. Some hepatocytes even have more than 1 nucleus (polyploidy).

I still don't know how I went through my cell biology class in sophomore year without understanding this. Maybe I missed the forest for the trees (curse you clathrin mediated endocytosis!)

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Muscles also have more than one nucleus per cell, if you have strength trained. You can fast and diet and waste away all the protein and shrink them down, but the nuclei remain. Go in to a surge of calories, protein, (and optional androgenic hormone signaling) and the nuclei effectively parallel process transcription of mRNA in the ribosomes for regeneration of the proteins from amino acids and re-bulking up of the cells and your strength.

This, (along with neural adaption) is what we are taking about when we reference “muscle memory”. It’s a steep hill to train the first time and multiply the nuclei, but once you have them, you have them for life, and subsequent re-strengthening efforts will be far easier.

I’ve gone through this myself and it’s pretty shocking. It took me X years to achieve Y kilograms barbell whatever movement. A diet or lack of training for a year and I can only do Y/2. But if I eat a ton, I can be back to Y or higher in a few months.

That’s the mechanism? It makes sense. It was trivial for me to return to my strength after an accident that left me hobbled for months but progress beyond is just as hard as originally. Cool.

That's part of the mechanism.

The fusion of single nucleus myoblasts into multi nuclei myofibers is clear at this link...quite neat

https://en.wikipedia.org/wiki/Myogenesis

It’s always refreshing for me to hear share what they did _not_ know, especially when it’s seems like “something obvious” that they absolutely “should” have known. Thanks for being honest and open - I can personally really relate to this anecdote, and also in the context of biology, genetics, etc.

Surely it's obvious even before finishing high school that everything you are taught in science is at best a partial truth and that this is especially true when you are young and inexperienced. Newton's laws are an approximation to reality at low velocities so we learnt them knowing that it was not the whole story but was good enough for a huge amount of work. In my Applied Physics degree (50 years ago) we didn't do General Relativity, there simply wasn't time to learn the relevant mathematics as well as everything else so we made do with Special Relativity. And so on.

I do agree though that some teachers do give the impression that what they tell you is the whole truth, perhaps I was lucky in mine being mostly more enlightened.

> For example, erythrocytes (RBCs) don't have nucleus and mitochondria.

They are less of an outlier when you find out that they start out with a nucleus but pinch it off and let white blood cells eat it when they near maturity.

https://wi.mit.edu/news/how-red-blood-cells-nuke-their-nucle...

They also shed their mitochondria at about the same time. Both make more room for hemoglobin, optimizing them for oxygen transport.

Yep! I vaguely remember my professor mentioning about this in my Immunology class when we were on the topic of recognizing self vs non-self. Something about MHC1 vs CD47 on RBCs. It's been a while. Fascinating stuff!

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