Pacini Corpuscles they are one of the four types of mechanoreceptors that enable the sense of touch, both in humans and in other species of mammals.
Thanks to these cells, we can sense the pressure and vibration on our skin, which is of key importance in detecting both possible physical threats and in such everyday aspects as the taking of objects in the environment.
It may seem like being so small doesn’t mean much on its own, but neuroscience has approached them very extensively as they are relevant to both our behavior and our survival i.e. point of view of psychology and biology. Let’s see what these little structures are doing that we all have in our biggest organ, the skin.
What are Pacini’s corpuscles?
Beyond the simplistic idea that humans 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. . Usually under the label of “touching” are grouped several of them, some of which are capable of generating very different experiences from each other.
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 particularly sensitive to the pressure and vibrations that can occur on the skin, either by touching an object or by the action of a particular private movement. These cells are named after their discoverer, the Italian anatomist Filippo Pacini.
These corpuscles, although present all over the skin, are mostly found in places where no hair is found, such as the palms of the hands, toes, and soles of the feet. They have a capacity to adapt very quickly to physical stimuli, allowing a rapid signal to be sent to the nervous system but gradually diminishing as the stimulus remains in contact with the skin.
Thanks to this type of cells, humans can detect physical aspects of objects such as their surface texture, roughness, In addition to exerting the appropriate force depending on whether we want to grab or release the object in question.
What function do they have?
Lamellar or Pacini corpuscles are cells that respond to sensory stimuli and any rapid changes that may occur in them. This is why its main function is to detect the vibrations of the skin, as well as the changes in pressure that this tissue may receive.
When a deformity or vibrational movement occurs in the skin, the corpuscles emit an action potential at the nerve ending, thus sending a signal to the nervous system and eventually reaching the brain.
Thanks to their great sensitivity, these corpuscles can detect vibrations of a frequency close to 250 hertz (Hz). This, to be understood, means that human skin is able to detect the movement of particles close to a micron (1 micron) in size at the fingertips. However, some studies have pointed out that they are able to activate in the face of vibrations in ranges between 30 and 100 Hz.
Where are they and how are they?
Structurally, Pacini corpuscles they have an oval shape, sometimes very similar to that of a cylinder. Its size is about a millimeter in length.
these cells they are made up of several leaves, also called lamellae, And it is for this reason that its other name is that of lamellar corpuscles. These layers can range from 20 to 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, gelatinous consistency and a high percentage of water.
At the bottom of the corpuscle between a nerve fiber protected by myelin, Which reaches the central part of the cell, becoming thicker and demyelinating as it is introduced into the corpuscle. In addition, several blood vessels also enter through this lower part, which branch out into the different lamellar layers that make up the mechanoreceptor.
Pacini Corpuscles they are located in the hypodermis of the whole body. This layer of skin is found deep within the tissue, but has different concentrations of lamellar corpuscles depending on the area of the body.
Although they can be found on both hairy and hairless skin, that is, those that do not have hair, they are much more numerous in the hairless parts, such as the palms of the hands and palms. feet. In fact, around 350 corpuscles can be found on each finger, And about 800 in the palms.
Despite this, compared to other types of sensory cells related to the sense of touch, Pacini cells are found in a smaller proportion. It should also be noted that the other three types of touch cells, namely those of Meissner, Merkel and Ruffini, are smaller than those of Pacini.
It is interesting to mention the fact that not only Pacini’s corpuscles can be found in human skin, but also in other more internal structures of the organism. Lamellar cells are found in places as diverse as they are the liver, sexual organs, pancreas, periosteum and mesentery. It was hypothesized that these cells would have the function of detecting mechanical vibrations by movement in these particular organs, to detect low frequency sounds.
Pacini’s corpuscles respond by sending signals to the nervous system when their lamellae are distorted. This deformation causes both deformation and pressure on the cell membrane of the sensory terminal. In turn, this membrane deforms or bends, and it is at this point that the nerve signal is sent to the central nervous structures, both the spinal cord and the brain.
This signal transmission has an electrochemical explanation. By deforming the cytoplasmic membrane of the sensory neuron, the pressure-sensitive sodium channels open. In this way, sodium ions (Na +) are released into the synaptic space, causing the cell membrane to depolarize and the generation of the action potential, resulting in a nerve impulse.
Pacini Corpuscles they respond according to the degree of pressure exerted on the skin. In other words, the more pressure there is, the more nerve signals are sent. It is for this reason that we are able to distinguish between a soft and delicate caress and a raclette that can hurt us.
However, there is also another phenomenon that may seem contrary to this fact, and that is that in the case of receptors that adapt quickly to stimuli, after a short period of time they begin to send less signals to the nervous system. central. For this reason, and after a short period of time, if we touch an object, it reaches the point where its touch becomes less conscious; this information is no longer so useful, beyond the first moment we know that the material reality that produces this sensation is there and is constantly affecting us.
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- Biswas, A. et al. (2015). Multilayer multilayer biomechanical model of the Pacinian corpuscle. IEEE transactions on Haptics 8 (1): pages 31 to 42.
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- Kandel, E. (2000). Principles of neural science. New York: McGraw-Hill, Health Professions Division.
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