The sense of touch that our skin allows is so innate and essential to our identity, but how much do we know about our skin and how it allows us to feel touch?
Follow this series of posts on touch to learn more.
We can think of our skin as our interface with the world; it gives us shape, it defines who we are and it allows us to feel and interact with the outside world.
Of all our senses, our sense of touch has the largest surface area, and unsurprisingly, our tactile perception, this sense of touch, is our earliest sense to develop (MacLean, 2008, Bremner and Spence, 2017). Before any of our senses, touch helps us understand and navigate our mother’s wombs, at an age of 8 weeks old, we can feel a touch on our cheeks (Krishna, 2012).
We can think of our skin as our interface with the world; it gives us shape, it defines who we are and it allows us to feel and interact with the outside world.List of low-treshold mechanoreceptors and properties
Low-threshold mechanoreceptors are a group of receptors that encode the versatile sense of touch through slightly different dynamics. They are divided into 4 main groups; Meissner Corpuscle (SA1), Pacinian Corpuscle (PC), which are both fast-adapters to a tactile stimuli; Ruffini endings (SA2) and Merkel cell which both adapt slower (McGlone et al., 2014).
They activate A-beta afferent nerves which are rapidly conducting myelinated nerve fibres meaning that the information encoded reaches the central nervous system rapidly, allowing acute response to these sensations.
These tactile receptors are therefore crucial for detecting and identifying objects. Moreover, they have differing sizes of receptive fields, allowing them to either localise information to a small surface area or to sum responses from a large area to encode general characteristics of pressure or heat. While Merkel cells are reported to reach 500 cm-2 densities in the fingertip, Meissner corpuscles are 5 times less, and Pacinian corpuscles, which with receptor sizes visible to the human eye, are fewer than 1000 in each hand (Bolton et al 1966).
The great depth of knowledge we have these receptors dates back to the early 1900s , with Weber in 1834 pioneering the study of the perceptual characteristics of our skin by defining a “two-point discrimination task:” “the distance between compass points necessary to feel two contacts,” which is still used today (Adrian and Umrath, 1929, Lundborg and Rosen, 2004).
Stay tuned for more information in our next post...