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

Ruffini's corpuscles They are a type of mechanoreceptors that are in charge, especially, of the perception of temperature, which could be considered as a subcomponent of the sense of touch.

Although they are very small cells, the truth is that without them we could not properly detect when we are in an environment in which we can catch cold or die from a heat wave, in addition to being important in detecting stretching of the body.

Neurobiology has been in charge of studying this component of the human sensory system, describing it and classifying it in the way it is described in this article. Let us understand how Ruffini corpuscles are and work below.

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What are Ruffini's corpuscles?

Ruffini's corpuscles, also called bulbous corpuscles, are cells which detect sensory stimuli at the skin level, having an important role constituting and forming the sense of touch. They get their name from the surname of the person who discovered them, Angelo Ruffini, a notable Italian doctor and biologist.

They are a type of mechanoreceptors that detect changes in temperature and stretching of the skin. They have the ability to detect signals within very small receptive fields, which makes them fall into the category of type I mechanoreceptors. They are not very numerous nor do they have a large size.

It has been seen that deep skin changes due to scars, degenerative processes, Aging or bad disposition of the joints can alter the location of these corpuscles.

What are these cells?

Ruffini's corpuscles are made up of many free nerve endings, which have their origin in a myelinated axon and constitute a cylindrical-shaped structure. This structure, which has the appearance of a capsule, organizes the nerve endings by anchoring between connective tissue collagen fibers. The axon demyelinates and further bifurcates into two, before forming branching nerve endings.

Despite this, it can be said that there are some differences between Ruffini's corpuscles in hairy skin and those found in glabrous skin. An example of this is in the penis, especially in the prepuce, where the corpuscles originate from a single axon which branches several times before becoming completely demyelinated within the tissue capsule connective.

On the other hand, in the case of hairy skin, the axon takes the shape of a spiral that approaches the hair follicle just below the sebaceous gland, where it branches and loses myelin.

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Where are they?

Ruffini's corpuscles are found both in hairy and glabrous skin, that is, in which there are no hairs, and also in both the hypodermis and epidermis. They are also found in non-superficial structures, such as the menisci, cruciate and lateral ligaments. and joint capsules. These cells can be found in most mammals.

However, and despite being found throughout the skin, there are differences in the level at which these corpuscles are found depending on whether there is hair or not. In the case of glabrous surfaces, such as the palms and fingers, soles of the feet, lips, penis and pubis, these cells are found at the level of the reticular layer of the epidermis.

Although in the case of structures in which there is hair, Ruffini's corpuscles are also found in the reticular layer of the epidermis, between hair and hair, in addition to being located in the connective tissue capsule that covers the part of the hair that is inserted at a certain depth in the fur. The group formed by this type of cell and the capsule is called the pilo-Ruffini complex..

In the animal world, in addition to the areas we have mentioned, these corpuscles are found in somewhat peculiar places. In the case of some primates, they have been found associated with regions of the dermis close to the hairs found on the nasal mucosa. In birds and some mammals it has been possible to see that Ruffini cells are found in joints, but only in the fibrous part and in the ligaments.

What role do they play?

The main function of Ruffini's corpuscles is the perception of temperature changes, in addition to the stretching of the skin. Also they can perceive the continuous deformation of the skin and more internal tissues.

These structures are of vital importance since they are the ones that allow the detection of temperature variations, especially taking the body's own temperature as a reference, thus establishing whether the environment is colder or warmer and how nice it is. They are also capable of detecting mechanical deformation of the skin, although this function is more typical of other mechanoreceptors, such as the Pacini corpuscles.

In fact, they differ from this other type of skin receptors in that Ruffini's corpuscles are slow to adapt. This means that are able to detect sustained stimuli on the skin, in addition to the slight stretching that can be exerted on this tissue.

Of note is the fact that they are not only able to detect stretch, but also perceive the joint angle, the speed of the mechanical stimulus on the skin and the type of stretching.

General aspects of mechanoreceptors

In the sense of touch they have a leading role up to four different types of mechanoreceptors. One of them is the Ruffini corpuscle, in addition to those of Pacini, Merkel and Meissner.

All of them have in common that they are found in the skin, and respond to physical changes that can occur on this tissue. They act as if they were signal transducer systems, converting mechanical stimulation into stimulation electrochemical, being sent to the central nervous system to be able to organize a response in case it is necessary.

The signals are sent in the form of burst nerve discharges, and depending on the characteristics of the sensory cell itself, such as the type of stimulus it is responsible for, the stimulation will be continuous or, on the other hand, it will progressively decrease.

These types of cells have been classified based on their behavior during the course of two phases: dynamic and static. Dynamic phase refers to the moment in which the intensity of the stimulus varies, for example, when heat is applied and stopped being applied to the skin. On the other hand, the static phase is understood as the moment in which the stimulus does not change its stimulation intensity on the organism.

Those receptors that are only stimulated during the dynamic phase have been called rapidly adapting or phasic mechanoreceptors, and it is the case of the Pacini corpuscles.

In contrast, those that are stimulated during both the dynamic and static phases are known as slow adaptive mechanoreceptors, being the case of those of Ruffini.

On the other hand, there is a second classification, depending on the size of the area that these types of receivers are in charge of. Type I receptors are those that receive signals or are responsible for the stimulation of small receptive fields, while type II receptors are responsible for larger receptive fields.

Bibliographic references:

• Halata, Z. (1988). Chapter 24. Ruffini corpuscle a stretch receptor in the connective tissue of the skin and locomotion apparatus. Transduction and Cellular Mechanisms in Sensory Receptors, 221-229.
• Paré M., Behets C., Cornu O. (2003). Paucity of presumptive ruffini corpuscles in the index finger pad of humans. The journal of comparative neurology; 456:260-266.