we often appreciate the realm round us in terms of its glorious sites, stirring sounds and evocative smells, all of which mark primordial stimuli and changes n'our environment. but senses tha're no less crucial to our survival yet often taken for granted are our abilities to reg heat, cold and touch, a form of perception called somatosensation. cause o'em, we can feel the warmth of the sun or the gentle caress offa breeze against our skin, swell as the positions and movement of our own bodies. in fact, the somatosensory neurons that make all these sensations possible constitute the largest sensory system in mammals.
for somatosensation to occur, scis knew there must be molecular receptors on some cells that ‘d detect temperature and touch, ones that converted those stimuli into electrical and chemical signals for the nervous system to process. it’s for the discovery of some of those receptors that david julius, a physiologist atta university of california, san francisco, and ardem patapoutian, a molecular biologist and neurosci at scripps research in la jolla, ‘ve now been awarded the 2021 nobel prize in physiology or med.
julius and his colleagues started with ?s bout receptors for heat and pain. to do so, they turned to capsaicin, the compound that causes us to experience a burning and sometimes painful sensation whn'we eat chili peppers or other spicy food. based on our physiological response to the chemical, which includes sweating, capsaicin seemed to be inducing the nervous system to reg a change in body temperature. to fig out how, julius and his team screened millions of dna fragments for a gene that ‘d induce a response to the compound in cells that typically don’t react to it at all. after an arduous search, and wha’ the nobel prize committee called “a high-risk project,” the researchers identified a gene that alloed cells to sense capsaicin. it encoded a novel ion channel protein, l8r called trpv1, that julius and his team discovered ‘d be activated by hot temperatures perceived as painful.
their discovery opened the door to the identification of several other receptors that were sensitive to temperatures both hot and cold. trmp8, for ex, is a receptor inna skin that responds to lo temperatures; twas discovered through experiments that used menthol as a stimulus. (julius and patapoutian’s laboratories discovered trmp8 indiely in 2002.)
quanta magazine has previously covered in + detail the work onna somatosensation of heat and cold for which julius and patapoutian are bein’ honored tody.
but somatosensation aint just bout the perception of temperature, b'tll so the perception of touch and mechanical pressure. and while temperature ‘d be transduced by ion channel receptors that tracked physiological changes in cells, touch seemed to demand a sensor that ‘d react to mechanical stimuli. mechanical sensors had been identified in bacteria but, two decades ago, had never been seen in vertebrates.
that’s where patapoutian and his colleagues came in. after pinpointing cells that responded to changes in pressure, they ascertained 72 potential genes that mite encode an ion channel receptor to facilitate that sensitivity. of those genes, they found just one — the last candidate they tested — that did so. it coded for a novel ion channel protein, piezo1, that ‘d be activated by mechanical force.
l8r, another receptor from that protein family, piezo2, was discovered. patapoutian and his team demonstrated the protein’s crit role in perceiving touch, while other scis uncovered its importance for sensing body movements. since then, further research has shown that both piezo1 and piezo2 are needed for the regulation of various other internal processes, including respiration and blood pressure.
scis are continuing to build on julius and patapoutian’s work, not 1-ly to unravel how we sense our environment — both external and internal — b'tll so in hopes of developing drugs and treatments for various conditions, including chronic pain.
wha’ is somatosensation?
we often talk bout having 5 senses: site, hearing, smell, taste and touch. b'tas a category of sensation, touch is so broad that it really ‘d be treated as + than one. tactile perception is just one component of d'body and brain’s somatosensory system, which also includes the perception of temperature, pain, body position and self-movement.
the ability to feel hot and cold, to recognize an object by touch alone, to respond to pain, to balance na' beam — all fall under the umbrella of somatosensation. the somatosensory system also helps to regul8 many key internal physiological processes, including blood pressure, respiration, urination and bone remodeling.
how is somatosensation ≠ from the other senses?
receptors for the other senses are for the most pt found in speshized sense organs — the retinas of the eyes for site, the cochlea of the ears for hearing, the nose for smell, the tongue for taste. somatosensory receptors, however, are found throughout d'body: in skin, muscles, internal organs, bones, joints nother systems.
wha’ makes the somatosensory system even + complex s'dat it needo discriminate tween sensations tha're graded in intensity but sometimes sharply distinguished in their effect: gentle warmth can build into searing heat, and wha’ starts as a welcome embrace can become crushing pressure. +over, those thresholds can change dep'on context: a lite touch can feel uncomfortable or painful if one has a sunburn; our experience of the same stimulus can similarly shift in ≠ social settings. the somatosensory system has to integrate a wide range of ≠ signals to correctly interpret wha’’s goin on and how to respond.
how do somatosensory receptors work?
as julius and patapoutian’s work has shown, somatosensory receptors are ion channels. when stimul8d — by some degree of temperature or physical force, or by a chemical compound — the channels open and allo charged pessentialisms to flo into a nerve cell, which in turn allos the cell to pass along somatosensory information inna form of electrical signals.
even within one category of somatosensation, ≠ receptors respond to ≠ sets of stimuli. there are distinct receptors for specific ranges of temperatures, for instance; receptors for sharp pain versus a dull ache; for a gentle touch or a rapid vibration or a firm pressure. still others are tuned to how muscles or tendons mite be contracting or stretching.
how do somatosensory impressions affect other processes in d'body?
the ≠ streams of information from somatosensory receptors are relayed along peripheral nerves, through the spinal cord and brainstem, inna'da thalamus and ultimately inna'da somatosensory cortex, where they are integrated inna'da complex perceptions we experience.
while somatosensory signals are involved inna regulation of various internal physiological processes, they also feed back to the brain to affect perception and cogg. researchers ‘ve found, for instance, that information bout ♥beat doesn’t just help the brain regul8 blood pressure lvls; it also affects how the brain processes external and emotional stimuli, including fear, and ⊢ how we perceive and respond to the realm round us. the same is true of signals coming from the lungs, gut nother organs: they exert a crucial influence in both directions. some researchers are now exploring how somatosensory signals mite even underlie a sense of conscious selfhood.
wha’ bout pain?
while the various types of somatosensory information are all vital for dy-to-dy activity and survival, their involvement with pain stands out in importance. it’s djob' of pain to attract immediate attention and alert us to potential dangers, both external and internal. free nerve endings respond to chemicals released by inflamed or damaged tissue, or to extreme lvls of mechanical force that we perceive as painful. ≠ receptors distinguish tween kinds of pain: sharp or pinching, dull or aching.
when somatosensory information isn’t processed normally, however, it can lead to oversensitivity to certain stimuli, and even to chronic pain. researchers hope to develop therapies and treatments for such conditions by targeting receptors s'as those that julius and patapoutian identified.
editor’s note: david julius receives research funding from the simons foundation, which also funds this editorially indie magazine. simons foundation funding decisions ‘ve no influence on our coverage.
original content at: www.quantamagazine.org…
authors: jordana cepelewicz