A type of mechanoreceptor distributed throughout the skin and various internal organs.
Pacini corpuscles are one of the four types of mechanoreceptors that allow the sense of touch, both in humans and in other mammalian species.
Thanks to these cells we can detect the pressure and vibrations on our skin, being of key importance when detecting both possible physical threats and in aspects as everyday 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 do in our largest organ, the skin.
What are Pacini corpuscles?
Beyond the simplistic idea that human beings have five senses, there is the 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, under the label of “touch” several of them are grouped, some of which are capable of generating very different experiences from each other.
Pacini corpuscles, also called lamellar corpuscles, are one of the four types of mechanoreceptors in charge of the sense of touch, found in human skin. They are especially sensitive to pressure and vibrations that can occur on the skin, either by touching an object or by the action of some movement of the individual. 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 fast ability to adapt to physical stimuli, allowing a fast signal to be sent to the nervous system but progressively decreasing 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 role do they play?
Lamellar or Pacini corpuscles are cells that respond to sensory stimuli and to 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 can 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 great sensitivity, these corpuscles can detect vibrations of a frequency close to 250 hertz (Hz). This, for the sake of understanding, means that human skin is capable of detecting the movement of particles close to one micron (1 μm) in size on the fingertips. However, some studies have pointed out that they are capable of being activated by vibrations in the ranges of 30 to 100 Hz.
Where are they and what are they like?
Structurally, the corpuscles of Pacini have an oval shape, sometimes very similar to that of a cylinder. Its size is around a millimeter in length more or less.
These cells are made up of several sheets, also called lamellae, and it is for this reason that their 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.
A nerve fiber protected by myelin enters the lower part of the corpuscle , 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, which branch into the various lamellar layers that make up the mechanoreceptor.
Pacini corpuscles are located in the hypodermis of the entire body. This layer of the skin is found in the deepest part of 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 areas, such as the palms of the hands and feet. In fact, about 350 corpuscles can be found on each finger of the hands, and about 800 on the palms.
Despite this, in comparison with other types of sensory cells related to the sense of touch, Pacini cells are found in a lower proportion. It should also be said that the other three types of touch cells, that is, those of Meissner, Merkel and Ruffini are smaller than those of Pacini.
It is interesting to mention the fact that Pacini corpuscles can not only be found in human skin, but also in other more internal structures of the body. 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 due to 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 deformation and pressure on the cell membrane of the sensory terminal to occur. In turn, this membrane is deformed or curved, and it is then that the nerve signal is sent to the central nervous structures, both the spinal cord and the brain.
This signaling has an electrochemical explanation. As the cytoplasmic membrane of the sensory neuron deforms, the sodium channels, which are pressure sensitive, open. In this way, sodium ions (Na +) are released into the synaptic space, causing the cell membrane to depolarize and generate the action potential, 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. 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 also another phenomenon that may seem contrary to this fact, and that is that since they are receptors for rapid adaptation 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 arrives at which its touch becomes less conscious; 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.
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