Pacinian corpuscles: what are they and how do these receptors work?

A type of mechanoreceptor distributed throughout the skin and various internal organs.

Pacini's corpuscles are one of the four types of mechanoreceptors that enable the sense of touch, both in humans and in other mammalian species.

Thanks to these cells, we can detect pressure and vibrations on our skin, which are of key importance in detecting possible physical threats as well as in everyday aspects such as picking up 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.

What are Pacini's corpuscles?

Beyond the simplistic idea that the human being has five senses, there is the reality: there is a wider variety of sensory pathways that inform us about what is happening both in our environment and in our body. Usually, several of them are grouped together under the label "touch", some of which are capable of generating very different experiences from one another.

Pacini's corpuscles, also called lamellar corpuscles, are one of four types of mechanoreceptors. one of the four types of mechanoreceptors responsible for the sense of touch found in human skin.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 throughout the skin, are found to a greater extent in places where there is no hair, such as the palms of the hands, fingers and soles of the feet. They have a very rapid capacity to adapt to physical stimuli, allowing a fast signal to be sent to the nervous system but gradually decreasing as the stimulus continues to be in contact with the skin.

Thanks to this type of cell, human beings are able to detect physical aspects of objects such as their surface texture, their roughness, as well as to exert the appropriate force on the skin.and also exert the appropriate force based on whether we want to grasp or release the object in question.

What is their function?

Lamellar corpuscles or Pacini's corpuscles are cells that respond to sensory stimuli and possible rapid changes that may occur in it. 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 that ends up reaching the brain.

Thanks to their high sensitivity, these corpuscles can detect vibrations of a frequency close to allow the detection of vibrations with a frequency of about 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) at the fingertips. However, some studies have suggested that they are capable of activating to vibrations in the 30 to 100 Hz range.

Where are they located and what do they look like?

Structurally, Pacini's corpuscles have an oval shape, sometimes very similar to that of a cylinder. have an oval shape, sometimes very similar to that of a cylinder.. Their size is about a millimeter or so in length.

These cells are made up of several lamellae, also called lamellaeand it is for this reason that their other name is lamellar corpuscles. These layers can be between 20 and 60, and are formed by 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 fiber protected by myelin. a nerve fiber protected by myelinThe Blood vessel, which reaches the central part of the cell, becomes thicker and thicker and demyelinates as it enters 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.

Pacini's corpuscles are located in the hypodermis of the whole body.. This layer of the skin is located deep within 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 hairless skin, they are much more numerous in hairless areas such as the palms of the hands and feet. In fact, about 350 corpses can be found on the palms of the hands and feet, about 350 corpuscles can be found on each finger of the hands, and about 800 on the palms of the hands.and about 800 on the palms.

Nevertheless, compared to other sensory cell types related to the sense of touch, Pacini cells are found in smaller proportion. It should also be noted that the other three types of touch cells, i.e. Meissner's, Merkel's and Ruffini's cells are smaller in size than Pacini's cells.

It is interesting to mention the fact that not only Pacini corpuscles can be found in human skin, but also in other more internal structures of the organism. Lamellar cells are found in such varied 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 due to movement in these organs in particular, detecting low frequency sounds.

Mechanism of action

Pacinian corpuscles respond by emitting 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 is deformed or curved, and it is then when the nerve signal is sent to the central nervous structures, both spinal cord and brain.

This sending of signals has an electrochemical explanation.. When the cytoplasmic membrane of the sensory neuron is deformed, the sodium channels, which are sensitive to pressure, open. Thus, 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.

Pacini's corpuscles respond according to the degree of pressure exerted on the skin.. In other words, the more pressure, the more nerve signals are sent. 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, there is another phenomenon that may seem contrary to this fact, and that is that since these receptors 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, the point comes when we become less aware of its 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.

Bibliographical 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): pp. 31 - 42.
• Cherepnov, V.L.; Chadaeva, N.I. (1981). Some characteristics of soluble proteins of Pacinian corpuscles. Bulletin of Experimental Biology and Medicine. 91 (3): 346–348.
• Kandel, E. (2000). Principles of neural science. Nueva York: McGraw-Hill, Health Professions Division.
• O’Johnson, K. (2001). The Roles and Functions of Cutaneous Mechanoreceptors. Current opinion in Neurobiology, 11: pp. 455 - 461.