6 ms·

One of the surprises I got after being locally anesthetized for a surgery, was that I could no longer localize my arm in space without looking at it. Propriocep

One of the surprises I got after being locally anesthetized for a surgery, was that I could no longer localize my arm in space without looking at it. Proprioception is heavily based on the flow of air against our skin and hair. Some flowmeters are based on that principle, using a tiny mechanical hair that vibrates as air flows over it, and I've always felt robotics should just dump a whole bunch of them on their moving parts rather than rely on a few gyroscopes and servomotors to estimate their position in space.

fsckboy 5y ago
> Proprioception is heavily based on the flow of air against our skin and hair. feeling sensations on the skin doesn't tell you where the skin is...?
- ad404b8a372f2b9 5y ago
  It does, the air flow going downward on your skin tells you your arm went up. I recall my arm being very numb, I had to poke myself strongly to feel it, I could move it but I had no idea where it went without looking at it, multiple times I was surprised to find it in a spot I didn't know it was. As I recovered sensation in my skin I regained proprioception gradually. Really trippy experience.
  - jamiek88 5y ago
    I once woke up, sober, from a night at home alone watching tv, with a strange person in my bed. Their arm was resting on my stomach above the sheets. I could see it. It was terrifying. I freaked out and tried to throw that arm off me when I realized it was my own. I’d slept on it, gone numb and my sleepy brain considered it someone else’s arm.
t0mas88 5y ago
I've always learned that proprioception is a standalone thing, not based on the air moving over the skin etc, but really just your own nervous system telling you the position of your joints. Which together tells you where your arm is. As far as I know it would theoretically still work in a vacuum with your eyes closed.
- jameshart 5y ago
  Proprioception is the overall sense of knowing where your body parts are. You don’t just have a bunch of ‘proprioceptor’ nerves dedicated solely to that task, you have a whole wealth of signals coming into your brain that it aggregates into that overall sense. Similar to how vision isn’t just the raw signals on your optic nerve, but a whole machinery around filling in the details and blanks and saccades from memory and inference to constitute a full visual sense.
  - t0mas88 5y ago
    Jup, that’s what I meant. Your nerve cells sensing where things are as opposed to other external senses like skin touch being used to figure it out.
  - DoingIsLearning 5y ago
    > You don’t just have a bunch of ‘proprioceptor’ nerves dedicated solely to that task, Actually you do. Most animals have capsule joint receptors which are dedicated to sensing stretching/relaxing of the joint capsule tissue. This signal is then sent through dedicated nerve paths on the dorsal part of your spine.
    - jameshart 5y ago
      And... they aren't just used for proprioception. They also tell you how heavy things are when you pick them up, and sense vibrations, and help you sense changes in acceleration, which are distinct sensations from 'where in space are my hands right now.'
deleted 5y ago
[deleted]
teachrdan 5y ago
Is that really true? Anecdotally, I have no trouble keeping track of where my arm is when I have a coat and gloves on :) I wonder if there's a side effect of anesthesia that inhibits the body's kinesthetic sense. https://en.wikipedia.org/wiki/Proprioception#Proprioception_and_kinesthesia https://en.wikipedia.org/wiki/Proprioception#Proprioception_...
- ad404b8a372f2b9 5y ago
  A quick google search says muscles are the primary receptors in humans, before it was believed the joints played that role. From my experience with anesthesia I reckon it's a little bit of everything, with the sensation of different organs being weighed differently in the final estimation. Unless you're in a vacuum as suggested in another comment I don't think you could draw definitive conclusions on the role of the skin from wearing a coat, the air flow might be mostly prevented but the weight and friction of your coat over the top of your arm as you move would be essentially the same input.
  - camtarn 5y ago
    I think that linking skin sensations to proprioception is pretty dubious. Think about walking in a high gale. The air will be pressing your outer layers to your body in a way that adds extra 'weight', but there's not even the slightest sensation of phantom movement in your limbs. Maybe it's a very low-weighted input, but I very much doubt proprioception is 'heavily based' on it as you said earlier.
    - ad404b8a372f2b9 5y ago
      You don't get phantom movements when you get a deep tissue massage yet the muscles are very much involved. There is also literature on the role of the skin in proprioception in humans. That being said, heavily might be overstated, I wasn't trying to claim an authoritative view on the matter, only reporting what I felt while anesthesia was wearing off.
      - 5y ago

fsckboy 5y ago

> Proprioception is heavily based on the flow of air against our skin and hair. feeling sensations on the skin doesn't tell you where the skin is...?

ad404b8a372f2b9 5y ago
It does, the air flow going downward on your skin tells you your arm went up. I recall my arm being very numb, I had to poke myself strongly to feel it, I could move it but I had no idea where it went without looking at it, multiple times I was surprised to find it in a spot I didn't know it was. As I recovered sensation in my skin I regained proprioception gradually. Really trippy experience.
- jamiek88 5y ago
  I once woke up, sober, from a night at home alone watching tv, with a strange person in my bed. Their arm was resting on my stomach above the sheets. I could see it. It was terrifying. I freaked out and tried to throw that arm off me when I realized it was my own. I’d slept on it, gone numb and my sleepy brain considered it someone else’s arm.

t0mas88 5y ago

I've always learned that proprioception is a standalone thing, not based on the air moving over the skin etc, but really just your own nervous system telling you the position of your joints. Which together tells you where your arm is. As far as I know it would theoretically still work in a vacuum with your eyes closed.

jameshart 5y ago
Proprioception is the overall sense of knowing where your body parts are. You don’t just have a bunch of ‘proprioceptor’ nerves dedicated solely to that task, you have a whole wealth of signals coming into your brain that it aggregates into that overall sense. Similar to how vision isn’t just the raw signals on your optic nerve, but a whole machinery around filling in the details and blanks and saccades from memory and inference to constitute a full visual sense.
- t0mas88 5y ago
  Jup, that’s what I meant. Your nerve cells sensing where things are as opposed to other external senses like skin touch being used to figure it out.
- DoingIsLearning 5y ago
  > You don’t just have a bunch of ‘proprioceptor’ nerves dedicated solely to that task, Actually you do. Most animals have capsule joint receptors which are dedicated to sensing stretching/relaxing of the joint capsule tissue. This signal is then sent through dedicated nerve paths on the dorsal part of your spine.
  - jameshart 5y ago
    And... they aren't just used for proprioception. They also tell you how heavy things are when you pick them up, and sense vibrations, and help you sense changes in acceleration, which are distinct sensations from 'where in space are my hands right now.'

deleted 5y ago

[deleted]

teachrdan 5y ago

Is that really true? Anecdotally, I have no trouble keeping track of where my arm is when I have a coat and gloves on :) I wonder if there's a side effect of anesthesia that inhibits the body's kinesthetic sense. https://en.wikipedia.org/wiki/Proprioception#Proprioception_and_kinesthesia https://en.wikipedia.org/wiki/Proprioception#Proprioception_...

ad404b8a372f2b9 5y ago
A quick google search says muscles are the primary receptors in humans, before it was believed the joints played that role. From my experience with anesthesia I reckon it's a little bit of everything, with the sensation of different organs being weighed differently in the final estimation. Unless you're in a vacuum as suggested in another comment I don't think you could draw definitive conclusions on the role of the skin from wearing a coat, the air flow might be mostly prevented but the weight and friction of your coat over the top of your arm as you move would be essentially the same input.
- camtarn 5y ago
  I think that linking skin sensations to proprioception is pretty dubious. Think about walking in a high gale. The air will be pressing your outer layers to your body in a way that adds extra 'weight', but there's not even the slightest sensation of phantom movement in your limbs. Maybe it's a very low-weighted input, but I very much doubt proprioception is 'heavily based' on it as you said earlier.
  - ad404b8a372f2b9 5y ago
    You don't get phantom movements when you get a deep tissue massage yet the muscles are very much involved. There is also literature on the role of the skin in proprioception in humans. That being said, heavily might be overstated, I wasn't trying to claim an authoritative view on the matter, only reporting what I felt while anesthesia was wearing off.
    - 5y ago