New muscle layer discovered on the jaw | Hacker News Reader

New muscle layer discovered on the jaw

unibas.ch

this is just more proof to me that we, as a species, are far more confident of our maturity and understanding than we should be.

there is so much that we think we know, but that we actually don't, or are just plain wrong about.

Almost anyone familiar with human jaw muscles last week would have bet all the money in their wallet that all the muscles connected to the jaw were known, in their entirety.

Every single one of those people were incorrect.

What else will time prove that we are wrong about? not just as a species with a collective scientific pool of knowledge, but as individuals?

where are we each placing our misplaced confidence, and are we open to correction?

>Almost anyone familiar with human jaw muscles last week would have bet all the money in their wallet that all the muscles connected to the jaw were known, in their entirety.

I suppose that really depends on what you mean by familiarity, if it means a superficial knowledge I suppose you're right but if it is more than superficial knowledge then given this quote from the article:

"A look at historical anatomy studies and textbooks reveals that the structure of the masseter muscle has already raised questions in the past. In a previous edition of Gray’s Anatomy, from the year 1995, the editors also describe the masseter muscle as having three layers, although the cited studies were based on the jaw musculature of other species and partly contradicted one another."

and a few other quotes, it seems likely that quite a few people would at least have refused the bet.

I learned the wrong physics like the atom model for years and aren't using any of that knowledge. Well, it is wrong anyway.

Luckily, I don't have crippling student debt coming with that useless knowledge.

> I learned the wrong physics like the atom model for years and aren't using any of that knowledge.

To be fair - this is fairly common for most subjects and models are exactly that: models. I think of them as precise-enough framework to help an introductory learners to wrap their minds around the topic.

In biology we teach the structure of the cell (golgi, nuclei, etc) in introductory classes and students are typically left with the impression that ALL cells are like this. It hit me that not all cells are like this when I took embryology :)

> To be fair - this is fairly common for most subjects and models are exactly that: models.

At least, I would have expected the model to be either right or useful.

Neil Bohr's atom model is neither.

It's just a simplified model. It's often used for teaching the context of chemistry (1900s?) and is used as a stepping stone for teaching orbitals and energy states so I think it's a useful tool for pedagogy at the very least :)

> Neil Bohr's atom model is neither.

It enables stoichiometry, at least...

What is the "right" physics model ?

I’m not sure whether or not what you’re saying about jaw scientists (that a thing?) thinking they knew everything is true, but regardless, the fact that we are able to adapt to new discoveries and discuss them seems positive, not negative.

There’s a shit ton we don’t know or get wrong, but you gotta start some where.

ESP (extra sensory perception) coincidences have been too many in my life that I feel there must be a way for us to communicate telepathically.

If you're not open to correction then you're not doing science, you're doing dogma.

well there are a lot of scientists doing dogma and calling it science, I'm sure.

it's endemic with every profession and it drives me nuts; the immensity of the arrogance required to say that you truly know something (with any complexity at all) to the fullest extent it can be known.

We tend to be extremely overconfident in our knowledge and it usually takes a few disasters for new technologies to stabilise such that we don't regularly hurt or kill people. It's one reason why we should be extremely cautious in adopting new medical techniques. It should be at an almost glacial pace. That's all I'll say for now for reasons you can probably figure out.

It's always astonishing to find that the envelope of cutting edge knowledge is sometimes far closer than you think.

IE, jaw muscles hadn't been figured out yet.

That really doesn’t help with my faith in medicine. It’s not that doctors don’t know a lot of things that work for a lot of conditions, but when it comes to knowing why something works, things get a lot murkier. I cut them a lot of slack because we evolved by chance and there is no design documentation or even clear requirements to work with.

That’s really how it is.

Having lost someone to ILD and then personally going through increasingly debilitating and unnerving (ddx) occipital neuralgia/headache (is there even a difference) I’ve come to understand, however yet to accept fully, that we are on borrowed time that one should just appreciate the good fortune of, until one fine day we have to come face to face with the vast limitations/inabilities of medical science or go through its probability based guesswork while fluctuating between hope and despair.

I am not saying this pejoratively, rather just matter-of-factly.

It’s just sad and defeating.

I kind of get a kick out of the idea that no one actually knows how anti inflammatory painkillers actually work. There are tons of mysteries in our bodies

Can you expand on what you mean?

I ask because we know NSAIDs’ impact on the cyclooxygenase enzymatic pathways and the corresponding impact that the reduction of prostaglandins has on bodily inflammation.

might have gotten my otc medicine mixed up, acetaminophen is the painkiller that's still unknown i think. i would say a google search is probably more interesting that anything I have for you.

Aren't there new studies emerging regarding acetaminophen destroying the empathy (is this parasympathetic, or sympathetic?), due to nervous system harm?

We also don't really get how anaesthesia works. Like, the local pain interactions? All good. The general loss of consciousness? Nope.

Also asking for clarification here. We’ve made a lot of progress understanding the target nerve cell proteins of many general anesthetics. Certainly this is young research but I don’t feel like we’re completely in the dark - there’s been heaps of progress here just in my short, 30+ year life and even since I studied medicine last decade.

It's almost a tautology, but one that is adjacent to deep truths. We don't understand how consciousness emerges, so we can't explain how some relatively simple molecules temporarily suspend it.

We know a lot about local interactions, but the big picture isn't there yet. More, as you well know, is different.

,,That really doesn’t help with my faith in medicine''

Better knowledge of anatomy doesn't help medecine. Better knowledge of aging process and immunology is much more important for increasing human lifespan and decreasing human suffering, and the last 10 years gave us amazing improvements in the knowledge part.

That's a dismissive attitude of other people's suffering. I have never had debilitating migraines, but I feel compassion for people who experience them. I value any innovation that would alleviate their suffering, just as I hope others would feel about problems I have.

Research works by prioritizing it to places where people expect a return. My friend has a PhD in cancer research because this way she takes part in saving human lives with the highest probability/impact. She could of course go to study anatomy more instead, but as it has an opportunity cost of more people dying of cancer.

Not having faith in medicine, which had many breakthroughs in the past few years just because it doesn't prioritize low impact research is what I would call dismissive.

That's why having TMJD (popping, clicking, dysfunction of the jaw) sucks so much. Surgeons don't like to mess with the jaw at all unless it's a last resort because it's not very well understood. Some of us have had it for years and the only "treatment" we can get is hot water bottles and painkillers. Hopefully this discovery will change things.

I find absolutely nothing solves the tightness/clicking like vaporized cannabis herb, or edibles.

Did anyone else just spend a bunch of time moving their jaw in different directions after reading this?

Yep, the other guests in my domestic flight must be a little concerned.

sinus issues?

Coke fiend

Yep, with fingers on the back of the cheek to feel the muscle tighten.

"The arrangement of the muscle fibers, she says, suggests that this layer is involved in the stabilization of the lower jaw. It also appears to be the only part of the masseter that can pull the lower jaw backwards – that is, toward the ear."

My set of Netter's Anatomy flashcards from medical school a decade ago describe the functions of the deep fibers of masseter (the 2nd layer of the masseter muscle) as 'retracting' the mandible. Interestingly the cards also say -here I interpret as regarding the superficial layer of masseter - that "some of its fibers may protrude the mandible" (which makes sense if you look at the diagram).

What is lost in translation or reinterpretation in the quote you've posted is that retracting the mandible is either the function of the deep layer of masseter or instead the function of this newly discovered third 'coronoid' layer (or quite possibly, both); it is not as though anatomists thought 'how the jaw retracts' to be unanswered before today, but rather it seems they have been using an incorrect or perhaps incomplete picture.

Interestingly I can see the stark difference in depiction between Netter's diagram illustrating deep masseter [1] and this other one.[2]

I also note the description from Netters, which states that part of Masseter inserts on "the lateral surface of the coronoid process", describes pretty well the muscle being announced in this paper, as per their photographs.

[1] https://ranzcrpart1.fandom.com/wiki/Temporal_fossa:Masseter_...

[2] https://www.medspine.es/wp-content/uploads/2017/02/Sin-t%C3%...

Seems a surprise that this has taken so long to be discovered, as every motion seems to require two muscles--one to pull and the other to relax/lengthen.

It astonishes me how little help people can get for the very common TMD so I am not surprised to find anything is misunderstood about the functional anatomy of the jaw.

I've suffered since the age of 21, but the attacks are less frequent these days (I'm 35). I do not take any painkillers for it, even OTC. I have tried 6 or 7 "professionally-made" mouth guards, some of which cost thousands. None of them helped and would actually make it harder to sleep at night. I instead deal with it by using heat, massage (full body is key), exercise, and nutrition.

For the record, I am also blown away by how incompetent the medical and dental professions are at treating this. Tap your teeth on a piece of paper? Puh-leeze, that does nothing when your joints or muscles shift at different times of the day, and maybe 1 in 5 dentists actually know how to properly account for that based on my experience dealing with them over the years. And swear to god, if I hear another licensed and credentialed dentist describe my joint hypermobility as "your jaw is weird", I'm going to shit a brick.

AFAIK it’s most likely a connective tissue disorder as opposed to muscular. For this there is also little help and rarely diagnosed. But at least may help find answers for comorbidities that are often considered unrelated.

I had severe pain in this exact location. When diagnosing, I was suggested to get my wisdom teeth removed. When they were removed the oral surgeon suggested I wear teeth guards when sleeping, because I had severe wear on my molars.

So I'm not sure which of those (or both?) were the cause, but since removing my wisdom teeth I have worn a teeth guard every night, and I don't have that pain anymore.

Yes. First experienced TMJ pain as a teenager and almost overdosed on painkillers while trying to get rid of it at 3AM. Still recurrs about 2-3 times per year, but I've now learned to feel it coming on much earlier and start loading up on codiene in advance.

For other folks not familiar with these abbreviations, https://en.wikipedia.org/wiki/Temporomandibular_joint_dysfun...

I have been getting it 10+ times a year since my early 20s. Whenever it happens it's as terrifying as the very first time.

I had it a long time and was not sure the pain was localized in the jaw (was it the neck, shoulders, back?) or even the extent to which there was a physical lesion or it was how my brain was interpreting things.

My dentist told me I was grinding my teeth and prescribed a bite guard and within two weeks the pain got better but became very definitely focalized in the jaw and I noticed ‘popping’ as a symptom.

It has been about 1.5 years since the diagnosis. last summer I went through a phase of throwing a lot of random food into a pot and hitting it with an immersion blender, getting shakes from Burger King whenever I felt like it, etc. I lost almost 20 kg.

I have been eating more normally since, it doesn’t bother me very often.

What sort of bite guard did you use? I clench my teeth like there's no tomorrow and I've discovered over the years that any bite guard that doesn't completely cover every tooth (on either the lower or upper arch) will eventually result in a supra-eruption of the exposed tooth, with drastic consequences for my bite.

Just one from the drugstore which you put in boiling water and then bite down on. It costs about $20.

It covers all the teeth on the top, but not the bottom.

My dentist said he could make one if that didn’t work out, but it did.

I’ve seen sketchy looking web sites by dentists who claim they can make something uniquely effective but it doesn’t look any different from the one I use so I don’t believe it.

I thought Botox helped?

Yes. Found this personal blog:

https://www.byrdie.com/botox-for-teeth-grinding

and scientific review paper:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5634354/

I'm sure it does but I am sure sham injections help too.

To me it seems a surprise that this has taken so long to be discovered in general. I thought we would know all muscles by now.

It’s been known about for at least 25 years, but there was some debate about the specifics. Thus they “described this layer in detail for the first time.”

It spent a good couple million years literally under our noses.

That statement leaves out the other muscles that pull the lower jaw backwards. It's making the discovery sound more sensational than it is.

How does a muscle go undiscovered for so long? I would have through we’d have dissected, autopsied and studied so many bodies in every way conceivable by now that there wouldn’t be anything else left to find?

I have never dissected a body, but I do know that they look nowhere like the textbook images. It’s all the same-ish color, lots of things are firmly attached to others, stuff is hiding other stuff from view, etc. I understand tracing the major nerves already is fairly difficult.

In addition, https://www.thestar.com/news/insight/2016/01/16/when-us-air-... doesn’t only apply to the outside of persons. The inside varies as much. Locations, sizes, connections, etc. all can vary. As an extreme examples, https://www.mentalfloss.com/article/91022/5-muscles-you-migh... lists 5 muscles that not every person has.

Also, if, as a student, you’re tasked to find the P parts of an object, there’s a strong tendency to search on when you only have found P-1, and to not go look for a P+1-st when you have found the P-th.

Look up how recently we figured out what fascia was responsible for. We are more confident in our knowledge then we should be. We have come a long way and have a much longer way to go.

It's not a new muscle. They're drawing a distinction between different parts of the masseter muscle. I showed this article to a dentist. They didn't think it was interesting.

> In a previous edition of Gray’s Anatomy, from the year 1995, the editors also describe the masseter muscle as having three layers

> Other individual studies from the early 2000s also reported three layers

So not entirely new.

Not entirely new, but apparently, not accepted by the medical community.

It is important to understand that human anatomy is a science discipline with as much debate as any other science discipline. No human body and therefore anatomy is like the other. This discovery isn't exactly new but a controversial topic with many different opinions under experts.

So mewing is real

I wonder if the various CGI human animation systems will be updated with this info.

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