Merkel discs occur in clusters beneath the ridges of the fingertips that make up fingerprints and their somewhat rigid structure. Merkel discs are not encapsulated, causing them to have a sustained response to mechanical pressure of the tissue. They fire fastest when small points indent the skin and fire at a low rate on flat surfaces.
Merkel nerve endings are extremely sensitive to pressure, and respond to pressure of less than 1 μm. Also, those with smaller fingers were better at distinguishing smaller grooves. And although women in general have smaller fingers than men, gender is not a factor. Men with smaller fingers have more sensitivity than women with larger fingers.
Researchers from McMaster University in Ontario, Canada, and Duquesne University in Pittsburgh tested the index fingers of 50 men and 50 women ages 18 to 27 for finger sensitivity. The study authors speculate that a higher density of Merkel cells may account for the extra sensitivity. The more Merkel cells, the more refined the sense of touch.
To find those Merkel cells, researchers measured the distance between the study participants' sweat pores. Merkel cells gather around those pores, and those with smaller fingers had higher sweat pore density. Ergo, they probably had more Merkel cells that were closer together.
"Neuroscientists have long known that some people have a better sense of touch than others, but the reasons for this difference have been mysterious," said Daniel Goldreich, a study co-author from McMaster University, in a news release. "Our discovery reveals that one important factor in the sense of touch is finger size."
