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

This type of mechanoreceptor allows us to detect tactile and temperature information.

Ruffini corpuscles are a type of mechanoreceptor responsible, in particular, for temperature perception, which could be considered a subcomponent of the sense of touch.

Although they are very small cells, the truth is that without them we would not be able to conveniently detect when we are in an environment where we can catch a cold or die from a heat wave, as well as being important in the detection of the stretching of the body.

Neurobiology has taken it upon itself to study this component of the human sensory system, describing and classifying it in the manner described in this article. Let's understand how Ruffini's corpuscles are and function below.

What are the corpuscles of Ruffini?

Ruffini's corpuscles, also called bulbous corpuscles, are cells which detect sensory stimuli at the cutaneous level, are cells which detect sensory stimuli at the cutaneous level, having an important role in constituting andThey play an important role in constituting and shaping the sense of touch. They get their name from the surname of their discoverer, Angelo Ruffini, a prominent Italian physician and biologist.

They are a type of mechanoreceptors that allow them to 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 are they very large in size.

It has been seen that deep skin alterations due to scarring, degenerative processes, aging or poor joint arrangement can alter the location of these corpuscles.

What are these cells like?

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

Nevertheless, 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 foreskin, where the corpuscles originate from a single axon which branches several times before completely demyelinating within the connective tissue capsule.

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

Where are they located?

Ruffini's corpuscles are found in both hairy and glabrous skin, i.e. skin without hair, as well as in the hypodermis and epidermis. They are also found in non-superficial structures such as menisci, cruciate and lateral ligaments and joint capsules. and joint capsules. These cells can be found in most mammals.

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

However, 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, as well as being located in the connective tissue capsule that lines the part of the hair that is inserted at a certain depth in the skin. The set formed by this type of cell and the capsule is called pilo-Ruffini complex..

In the animal world, in addition to the areas mentioned above, 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 in the nasal mucosa. In birds and some mammals, Ruffini cells have been found in joints, but only in the fibrous part and in ligaments.

What is their function?

The main function of Ruffini corpuscles is the perception of temperature changes, as well as skin stretching. Also They can also sense the continued deformation of the skin and innermost tissues..

These structures are of vital importance as they are able to detect temperature variations, especially in reference to the body's own temperature, thus establishing whether the environment is cooler or warmer and how comfortable it is. They are also capable of detecting mechanical deformation of the skin, although this function is more typical of other mechanoreceptors, such as Pacini's corpuscles.

In fact, they differ from these other types of skin receptors in that the Ruffini corpuscles are slow adapting. This means that are able to detect sustained stimuli on the skin, in addition to slight stretching of the skin.This means that they are capable of detecting sustained stimuli on the skin, in addition to the slight stretching that may be exerted on this tissue.

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

General aspects of mechanoreceptors

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

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

The signals are sent in the form of nerve burst discharges.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 be progressively diminished.

This type of cell has been classified according to its behavior during the course of two phases: dynamic and static. two phases: dynamic and static.. The dynamic phase refers to the moment when the intensity of the stimulus varies, e.g. when heat is applied to the skin and when it is no longer applied. 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 mechanoreceptors of rapid adaptation or phasic receptors, as in the case of cortices.This is the case of Pacini's corpuscles.

On the other hand, those that are stimulated during both the dynamic and static phases are known as slow adapting mechanoreceptorsRuffini's corpuscles are the case.

On the other hand, there is a second classification, there is a second classificationdepending on the size of the area that these types of receptors are responsible for. 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.

Bibliographical 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.