The Pacini corpuscles are one of the four types of mechanoreceptors that allow the sense of touch, both in humans and in other mammal species.

Thanks to these cells we can detect the pressure and vibrations on our skin, having a key importance when it comes to detecting possible physical threats as well as in such everyday aspects as taking objects from the environment.

They may not seem like much of a challenge because they are so small, but neuroscience has dealt with them very thoroughly. Let’s see what these little structures that we all have in our largest organ, our skin, do.

What are Pacini’s corpuscles?

Pacini’s corpuscles, also called lamellar corpuscles, are one of the four types of mechanoreceptors responsible for the sense of touch , found in human skin. They are especially sensitive to pressure and vibrations that may occur in the skin, either by touching an object or by the action of some movement of the individual himself. These cells are named after their discoverer, the Italian anatomist Filippo Pacini.

These corpuscles, although found all over the skin, are mostly found in places where no hair is found, such as the palms of the hands, fingers and soles of the feet. They have a very fast capacity of adaptation before the physical stimuli, allowing to send a fast signal towards the nervous system but progressively diminishing it as the stimulus continues being in contact with the skin.

Thanks to this type of cells, human beings can detect physical aspects of objects such as their surface texture, their roughness , as well as exert the appropriate force based on whether we want to grab or release the object in question.

What role do they play?

The lamellar or Pacini corpuscles are cells that respond to sensory stimuli and possible rapid changes in them. That is why their main function is to detect vibrations in the skin, as well as changes in the pressure that this tissue may receive.

When there is a deformation or vibrating movement in the skin, the corpuscles emit an action potential in the nerve terminal, thus sending a signal to the nervous system.

Thanks to their great sensitivity, these corpuscles allow the detection of vibrations of a frequency close to 250 Hertz (Hz) . This, to be understood, means that human skin is capable of detecting the movement of particles of a size close to one micron (1 μm) on the fingertips. However, some studies have suggested that they are capable of being activated by vibrations in the range of 30 to 100 Hz.

Where are they and what do they look like?

Structurally, Pacini’s corpuscles have an oval shape, sometimes very similar to that of a cylinder . Its size is about one millimeter long.

These cells are made up of several plates, also called lamellae , and it is for this reason that their other name is that of lamellar corpuscles. These layers can be between 20 and 60, and are made up of fibroblasts, a type of connective cell, and fibrous connective tissue. The lamellae do not have direct contact with each other, but are separated by very thin layers of collagen, with a gelatinous consistency and a high percentage of water.

In the lower part of the corpuscle enters a nerve fibre protected by myelin , which reaches the central part of the cell, becoming thicker and demyelinating as it enters the corpuscle. In addition, several blood vessels also penetrate through this lower part and branch out into the various lamellar layers that make up the mechanoreceptor.

Pacini’s corpuscles are located in the hypodermis of the whole body . This layer of skin is found deep within the tissue, however it has different concentrations of lamellar corpuscles depending on the area of the body.

Although they can be found on both hairy and glabrous skin, i.e. skin that does not have any hair, they are much more numerous on hairless parts, such as the palms and feet. In fact, you can find about 350 corpuscles on each finger , and about 800 on the palms.

However, compared to other types of sensory cells related to the sense of touch, Pacini cells are found in a smaller proportion. The other three types of touch cells, i.e. Meissner’s, Merkel’s and Ruffini’s, are also smaller than Pacini’s.

It is interesting to mention the fact that Pacini’s corpuscles can be found not only in human skin, but also in other more internal structures of the organism. Lamellar cells are found in such diverse places as the liver, sexual organs, pancreas, periosteum and mesentery . It has been hypothesized that these cells would have the function of detecting mechanical vibrations by movement in these specific organs, detecting low frequency sounds.

Mechanism of action

Pacini’s corpuscles respond by emitting signals to the nervous system when their lamellae are deformed. This deformation causes both the deformation and the pressure on the cell membrane of the sensory terminal. In turn, this membrane is deformed or curved, and that is when the nerve signal is sent to the central nerve structures, both the spinal cord and the brain.

This signal sending has an electrochemical explanation . When the cytoplasmic membrane of the sensory neuron is deformed, the sodium channels, which are sensitive to pressure, open. In this way, sodium (Na+) ions are released into the synaptic space, causing the cell membrane to depolarize and the action potential to be generated, giving rise to the nerve impulse.

Pacini’s corpuscles respond according to the degree of pressure exerted on the skin . That is, the more pressure, the more nerve signals are sent. That is why we are able to distinguish between a soft and delicate caress and a squeeze that can even hurt us.

However, there is another phenomenon that may seem to contradict this, and that is that as they are receivers of rapid adaptation to the stimuli, after a short time they begin to send fewer signals to the central nervous system. For this reason, and after a short period of time, if we are touching an object, the point comes when its touch becomes less conscious.

Bibliographic references:

  • Biswas, A. et al. (2015). Vibrotactile Sensitivity Threshold: Nonlinear Stochastic Mechanotransduction Model of the Pacinian Corpuscle. IEEE Transactions on Haptics 8(1). 102–113.
  • Biswas, A. et al. (2015). Multiscale Layered Biomechanical Model of the Pacinian Corpuscle. IEEE Transactions on Haptics 8(1). 31–42.
  • O’Johnson, K. (2001). The Roles and Functions of Cutaneous Mechanoreceptors. Current opinion in Neurobiology, 11. 455-461.