Pacinian Corpuscles: What They Are And How These Receptors Work
Pacini’s corpuscles They are one of the four types of mechanoreceptors that allow the sense of touch, both in humans and other mammalian species.
Thanks to these cells we can detect pressure and vibrations on our skin, having a key importance when it comes to detecting both possible physical threats and in such everyday aspects as taking objects from the environment.
It may seem that being so small they do not give much of themselves, however, neuroscience has addressed them very thoroughly, since they are relevant both in our behavior and in our survival, that is, from the point of view of Psychology. and Biology. Let’s see what these small structures that we all have in our largest organ, the skin, do.
Beyond the simplistic idea that human beings have five senses, there is reality: there is a greater variety of sensory pathways that inform us about what is happening both in our environment and in our body. Normally, several of them are grouped under the label of “touch”, some of which are capable of generating very different experiences from one another.
Pacinian 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 on the skin, either by touching an object or by the action of some movement of the individual themselves. These cells are named after their discoverer, the Italian anatomist Filippo Pacini.
These corpuscles, although they are found throughout the skin, are found to a greater extent in places where hair is not found, such as the palms of the hands, fingers and the soles of the feet. They have a very rapid capacity to adapt to physical stimuli, allowing a rapid signal to be sent to the nervous system but progressively decreasing it as the stimulus continues to be in contact with the skin.
Thanks to this type of cells, human beings can detect physical aspects of objects such as their surface texture, roughness in addition to exerting the appropriate force based on whether we want to grab or release the object in question.
What function do they play?
Lamellar or Pacinian corpuscles are cells that respond to sensory stimuli and the possible rapid changes that may occur in it. That is why its main function is to detect vibrations in the skin, in addition to changes in the pressure that this tissue may receive.
When a deformation or vibrating movement occurs in the skin, the corpuscles emit an action potential in the nerve terminal, thus sending a signal to the nervous system that ends up reaching the brain.
Thanks to their great sensitivity, these corpuscles allow detecting vibrations with a frequency close to 250 hertz (Hz) This, to be understood, means that human skin is capable of detecting the movement of particles close to a micron (1 μm) in size in the fingertips. However, some studies have suggested that they are capable of being activated by vibrations in ranges between 30 and 100 Hz.
Where are they located and what are they like?
Structurally, Pacinian corpuscles They have an oval shape, sometimes very similar to that of a cylinder Its size is around a millimeter in length or so.
These cells They are made up of several sheets, also called lamellae , and it is for this reason that its other name is 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.
At the bottom of the corpuscle enters a nerve fiber protected by myelin , which reaches the central part of the cell, becoming increasingly thicker and demyelinated as it is introduced into the corpuscle. In addition, several blood vessels also penetrate through this lower part, which branch into the various lamellar layers that make up the mechanoreceptor.
Pacinian corpuscles They are located in the hypodermis of the entire body This layer of skin is located deep in the tissue, however it has different concentrations of lamellar corpuscles depending on the area of ​​the body.
Although they can be found in both hairy and glabrous skin, that is, skin that does not have any hair, they are much more numerous in hairless parts, such as the palms of the hands and feet. In fact, About 350 corpuscles can be found in each finger of the hands and about 800 in the palms.
Despite this, compared to other types of sensory cells related to the sense of touch, Pacinian cells are found in a smaller proportion. It should also be said that the other three types of touch cells, that is, Meissner, Merkel and Ruffini cells, are smaller than Pacinian cells.
It is interesting to mention the fact that Pacinian corpuscles can not only be found in human skin, but also in other more internal structures of the body. Lamellar cells are found in places as diverse as they are the liver, sexual organs, pancreas, periosteum and mesentery It has been hypothesized that these cells would have the function of detecting mechanical vibrations caused by movement in these specific organs, detecting low-frequency sounds.
Pacinian corpuscles respond by sending signals to the nervous system when their lamellae are deformed. This deformation causes both deformation and pressure on the cell membrane of the sensory terminal. In turn, this membrane deforms or curves, and it is then that the nervous signal is sent to the central nervous structures, both the spinal cord and the brain.
This sending of signals has an electrochemical explanation When the cytoplasmic membrane of the sensory neuron deforms, the sodium channels, which are sensitive to pressure, open. In this way, sodium ions (Na+) 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.
Pacinian corpuscles respond according to the degree of pressure exerted on the skin That is, the more pressure, the greater the sending of nervous signals. It is for this reason that we are able to discern between a soft and delicate caress and a squeeze that can even hurt us.
However, another phenomenon also happens that may seem contrary to this fact, and that is that since they are receptors that adapt quickly to 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, there comes a point where we become less conscious of our touch; That information is no longer so useful, after the first moment in which we know that the material reality that produces that sensation is there and affects us constantly.
