Ruffini’s corpuscles are a type of mechanoreceptors that are especially responsible for the perception of temperature, which could be considered a sub-component of the sense of touch.

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

Neurobiology has taken on the task of studying 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 look and work below.

What are Ruffini’s corpuscles?

The Ruffini corpuscles, also called bulbous corpuscles, are cells which detect sensory stimuli at a cutaneous level , having an important role in constituting and forming the sense of touch. They are named after the discoverer, Angelo Ruffini, an outstanding Italian doctor and biologist.

They are a type of mechanoreceptors that allow to detect temperature changes and skin stretching . They have the ability to detect signals within very small receptive fields, which brings them into the category of type I mechanoreceptors. They are not very numerous or large in size.

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

What do these cells look like?

The corpuscles of Ruffini are formed by many free nerve endings , which originate from a myelinated axon and constitute a cylindrical structure. This structure, which has a capsule-like appearance, the nerve endings are organised by anchoring themselves between collagen fibres of connective tissue. The axon is demyelinated and later forks into two, before forming branched nerve endings.

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

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

Where are they?

Ruffini’s corpuscles are found in both hairy and hairless skin, and also in the hypodermis and epidermis. They are also found in non-surface structures, such as menisci, crossed and lateral ligaments and joint capsules. These cells can be found in most mammals.

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

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

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

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

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

General aspects of the mechanoreceptors

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

They all have in common that they are found in the skin, and respond to physical changes that can occur in this tissue. They act as if they were signal transducer systems, converting mechanical stimulation into electrochemical stimulation, being sent to the central nervous system in order to organize a response if necessary.

The signals are sent in the form of a burst of 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 either be continuous or, on the other hand, progressively decreased.

This type of cell has been classified according to its behavior during the course of two phases: the dynamic and the static . Dynamic phase refers to the moment when the intensity of the stimulus varies, for example when heat is applied and stopped on the skin. By contrast, the static phase is understood as the moment at which the stimulus does not change its intensity of stimulation on the organism.

Those receptors that are only stimulated during the dynamic phase have been called fast adapting or phasic mechanoreceptors , and 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 mechanoreceptors , being the case of Ruffini’s.

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 receivers are those that receive signals or are responsible for the stimulation of small receptive fields, while type II receivers 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.
  • I stopped 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.