The sensory system that processes touch is called the somatosensory system. This system also detects and relays information about proprioception (how your joints are positioned), temperature, internal organs, and some chemical stimuli (like capsaicin, found in hot chili peppers). All this sounds relatively straight forward, but this field has been changing really rapidly!
(1) Textbooks often write about 4 receptors in the hand that sense vibration and pressure: Meissner corpuscle, Merkel cells, Pacinian corpuscle, and Ruffini endings. Yet, there is controversy on whether Ruffini endings even exist![1] Also, the role of Merkel cells – whether they actually detect touch – lacks evidence [1].
(2) Pain detection is attributed to free nerve endings. A couple of labs have suggested that perhaps instead of receptors on the ends of neurons, information is transduced (detected) by glia [2]. This would mean an existence of a unique sensory organ that has not been characterized.
(3) Several receptors exist to convey and relay information about temperature; there are one to two receptors (TRP channels) for detecting warmth, intense heat, cool, and intense cold…. But the identity of these receptors are constantly being updated. Just earlier this year, additional evidence suggesting involvement of a cool/cold receptor in sensing warmth was published [3][4]. Additionally, some of the temperature sensitive receptors listed in textbooks are no longer related to temperature detection since they aren’t even expressed in neurons [5].
Pages can be dedicated to each of these ideas in a textbook (such as in Principles of Neuroscience), yet our understanding of somatosensation is constantly evolving. What’s taken for granted now may elicit an eye-roll in some years.
(My girlfriend suggested that I combine painting and embroidery on a canvas. The red, the veins, are still anatomically incorrect – the pattern depicted should be on the other side of the bones. The tan, the nerves, is also anatomically incorrect since there shouldn’t have a downward pattern. The paint chipping off when poking the canvas with a needle made this an unforgiving project.)
Originally posted on Instagram April 7, 2020
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