January 25th, 2020

A Balance

Sense of Touch - Our Skin's Mechanoreceptors

I've been reading about the human sense of touch and the receptors in our skin that detect touch, vibration, and pressure. There are actually four types of mechanoreceptors in human skin. Here's a summary of them with some quotes from Wikipedia:

Lamellar corpuscles (Pacinian corpuscles) - vibration

These are capsule-like structures that are composed of layers. The layers are "separated by gelatinous material" and so these structures are mostly water. There is a nerve running in a line down the center. From what I understand, vibrations cause the layers to compress and this causes a signal to be transmitted to the nervous system. They detect varying vibrations rather than steady vibrations. "Their optimal sensitivity is 250 Hz" and they "have a large receptive field on the skin's surface with an especially sensitive center." https://en.wikipedia.org/wiki/Lamellar_corpuscle

Tactile corpuscles (Meissner's corpuscles) - light touch

Like Lamellar corpuscles, these are capsule-like structures. However, in Tactile corpuscles, there are horizonal layers of cells and the nerve endings wind among them. In Lamellar corpuscles, the layers are in arc-shapes, like an onion, and the nerve runs in a straight line.

Tactile corpuscles sense touch and are located in the outer region of the dermis. "They have their highest sensitivity...when sensing vibrations between 10 and 50 Hz." https://en.wikipedia.org/wiki/Tactile_corpuscle

Bulbous corpuscles (Ruffini corpuscle) - stretch

These are disc-shaped capsules containing a branching structure of nerve endings. It doesn't seem to have layers the way that Lamellar or Tactile corpuscles do. They detect the stretching of the skin and help facilitate "kinesthetic sense of and control of finger position and movement." https://en.wikipedia.org/wiki/Bulbous_corpuscle

Merkel nerve endings - pressure

These are nerve endings, rather than corpuscles. They "provide information on mechanical pressure, position, and deep static touch features, such as shapes and edges... Merkel nerve endings are the most sensitive of the four main types of mechanoreceptors to vibrations at low frequencies, around 5 to 15 Hz." https://en.wikipedia.org/wiki/Merkel_nerve_ending

There's also an article on Pallesthesia, which is the ability to detect vibration through our skin. It's a concept used to identify conditions where this sense is reduced or not functioning properly.