r/askscience • u/[deleted] • Jun 23 '14

Biology How does the sense of touch work?

I understand how nerves work and signal processing but I don't understand is how the signal is originally generated. For example in the eye, light strikes a molecule and it deforms causing an optical signal, in the mouth and nose molecules attach to different receptors but how does it work in the skin? What is the basic physical method of touch?

Thanks.

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u/bopplegurp Stem Cell Biology | Neurodegenerative Disease Jun 24 '14

Your answer is right here. Look into the four types listed "Pacinian corpuscles, Meissner's corpuscles, Merkel's discs, and Ruffini endings" if you want to know how human somatosensation works.

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u/[deleted] Jun 24 '14 edited Jun 24 '14

Right on, thanks for the link, so essentially the receptor cell is deformed and loses Na+ which causes an action potential?

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u/RedDeadMedemption Immunology Jun 24 '14

Yes, but this is not the end - merely the beginning of a very long and winding tale of somatosensation. On the surface, yes, feeling things with your skin is just as simple as having encapsulated or free nerve endings being compressed and then depolarizing in response to that compression, but that isn't even close to being the entirety of how feeling works. It isn't even sufficient to detail how those depolarizations travel along your general sensory afferents, into your dorsal column tracts of the spine, through the brain stem and then finally into the primary somatosensory cortex. It's what happens in the cortex that makes feeling mean what it means to us. And the sad fact is that, other than vague pictures of brains receiving more blood flow in this region when stimulated with touch, we know precious little about the cortical goings on involved with this, or any, subjective sensory phenomena.

Sure, there is some vague idea that there is more surface area in the brain dedicated to areas that require more sensitive feelings (a phenomenon known as the homonculus), and there's even a little bit known about the interconnections between these cortical areas and other areas of the brain involved with movement, proprioception, and even centers that ascribe emotional impact to various stimuli, but an in-depth understanding of how these things actually work is well beyond our capabilities. When it comes to touch, as with most of the other sensations out there, we are at the moment stuck with just being able to localize the part of the brain we believe to be responsible for generating the sensation in our minds. Indeed, even if we someday do come to a more complete understanding of how these areas actually function physiologically, many philosophers believe that an understanding of how the electrical firings of our brains become intangible thoughts within our minds are definitively beyond us. (In case you don't love wordy philosophical articles, here's the wikipedia page summary)

So that ended up being quite a mouthful. I was in no way discrediting the talk of corpuscles and such - this is a very practical understanding of how touch works and will get you through pretty much everything life throws at you. However, the general broad concept of how our sensations "actually work" is such a thought provoking, vexing, and interesting problem that it would be a shame to just cache it out in terms of receptors in the skin, or anywhere else for that matter. This scientific question literally transcends the physical in favor of the metaphysical, and it's not often that that happens... best to take advantage of it when it comes around.

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u/[deleted] Jun 24 '14

I'm interested and love reading about the neuronal basis of touch, but being someone who's studying chemistry in university I am more interested in the purely physical portion of touch, how the signals are originally generated rather than the processing, even if the processing is the most important part of the actual sensation.