RUFFINI CORPUSCLES: HISTOLOGY, FUNCTIONS, MECHANISMS OF ACTION - BIOLOGY - 2025

The Ruffini corpuscles are responsive to mechanical stimuli and subtle variations in temperature sensory receptors. These consist of a single myelinated axon that branches into multiple nerve endings that anchor inside a capsule.

This capsule can be composed of collagen synthesized by fibroblasts or perineural cells. These receivers are named after the Italian physician and biologist Angelo Ruffini (1864-1929).

Ruffini corpuscles. By Angelo Ruffini (Life time: 1929),, from Wikimedia Commons.

They are located both in the dermis and in the hypodermis of the glabrous and hairy skin of mammals and marsupials, as well as in the menisci, ligaments and joint capsules of the joints of some birds and mammals.

The Ruffini corpuscles found in each of the above locations show slight variations in structure. However, all of them are mechanoreceptors that adapt slowly to stimuli and perceive stimuli in small receptive fields.

Ruffini corpuscles

They are cutaneous sensory receptors, that is, located in the skin, being specialized in perceiving temperature variations above or below body temperature. Additionally, they are capable of perceiving low levels of mechanical deformation of the skin, even in the deepest layers of the skin.

Slowly adapting mechanoreceptors are capable of detecting sustained or prolonged pressure stimuli on the skin, as well as slight deformations produced by stretching it. In addition to detecting these types of static stimuli, they also respond to dynamic factors such as joint angle, stimulus speed, and stretch.

Given their ability to detect signals with very small receptive fields, Ruffini endings fall within the classification of type I mechanoreceptors.

These corpuscles are quite small in size and are not very numerous.

It can be assumed that the structural change in the connective tissue (injuries, bad position of the joints, scars, degenerative processes, aging) also leads to a change in the corpuscles of Ruffini. All this because they adjust to the new surroundings.

Location

Ruffini's endings or corpuscles have been found both in the hairy and glabrous skin of mammals and marsupials and in the cruciate and lateral ligaments, menisci and joint capsules of the joints.

In glabrous skin or skin devoid of hair, present on the palms of the hands, soles of the feet, lips, pubis and penis, Ruffini's corpuscles are located at the level of the reticular layer of the epidermis.

Whereas, in hairy or hairy skin, these receptors are also arranged in the reticular layer of the epidermis between the hair follicles and in the capsule of connective tissue that lines the part of the hair or hair that is inserted into the skin. The set made up of the capsule and the mechanoreceptor has been called the Pilo-Ruffini Complex.

In primates, these corpuscles have also been found associated with the regions of the dermis close to the insertion of the hairs that line the nasal mucosa.

Finally, Ruffini's corpuscles found in the joint capsules of birds and mammals are located only in the areas that are inside the fibrous layer and the ligaments of the capsule.

Histology

They are made up of numerous free nerve endings, originating from a common myelinated axon, which are encapsulated forming a cylindrical structure. In this capsule, the nerve endings are anchored between collagen fibers of connective tissue. The axon loses the myelin sheath and bifurcates in two before encapsulating to form branched nerve endings.

The above description corresponds to the classical structure of a Ruffini corpuscle. However, there are usually subtle variations in the structure of Ruffini's corpuscles present in glabrous skin and in hairy skin that has different anatomical structures.

For example, Ruffini's corpuscles located in the glabrous skin of the foreskin usually originate from a single axon that branches several times before losing its myelin coating within the connective tissue capsule.

In the particular case of hairy skin, where the Pilo-Ruffini Complex can form, the axon forms a spiral that approaches the hair follicle just below the sebaceous gland, where it branches, losing myelin. The branches are anchored in the connective tissue capsule of the hair follicle.

Features

They perceive heat-related changes in temperature and record their stretching. Additionally, they identify the continuous deformation of the skin and deep tissues.

Mechanism of action

By applying a mechanical force to the skin, the capsule perceives said tension at its ends. Then the nerve endings are compressed around the collagen fibers. This compression is maintained for a time thanks to the inelasticity of collagen, therefore the stimulus is captured in response to prolonged stimulation.

Mechanoreceptors

Mechanoreceptors are sensory receptors located in the skin that respond to mechanical changes such as pressure. They do this thanks to the fact that they function as a signal transducer system.

That is, they are capable of capturing pressure, tension and distortion stimuli, interpreting them, and transmitting this information inside the cell in order to generate a physiological response.

The signal that is transmitted by these types of receptors is nervous. In other words, it consists of a repetitive electrical discharge produced by a change in the membrane potential. Which occurs as a consequence of the excitation or activation of the receptor by a given stimulus.

Classification of mechanoreceptors based on their function

Mechanoreceptors have been classified based on the response they are capable of giving during the two phases in which the stimulus is applied. The dynamic phase and the static phase.

The dynamic phase corresponds to the stage in which the intensity of the applied stimulus varies, such as when it is applied and when pressure is no longer applied to the skin. For its part, the static phase refers to the period of time in which the application of the stimulus is constant.

Mechanoreceptors that are only stimulated during the dynamic phase, generating a response, have been called rapidly adapting receptors or phasic receptors. Whereas, those that are capable of responding in either phase are known as slowly adapting receptors or tonic receptors.

These two main types of receptors can be subclassified into two more types based on the size of the area in which they can perceive stimuli, known in physiology as the receptive field.

These have been referred to as: type I receptors and type II receptors. Type I receptors perceive signals in limited areas or small receptive fields, while type II receptors do so in large receptive fields.

Finally, a final classification has been established in terms of function: Meissner corpuscles, Merckel disks, Paccini corpuscles and the aforementioned Ruffini corpuscles.

References

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2. Boyd A. The histological structure of the receptors in the knee joint of the cat correlated with their physiological response. J Physiol. 1954; 124: 476-488.
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4. 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.
5. Mountcastle, VC. (2005). The sensory hand: neuronal mechanisms of somatic sensation. Harvard University Press. Page 34.
6. Paré M, Behets C, Cornu O. Paucity of presumptive ruffini corpuscles in the index finger pad of humans. The journal of comparative neurology. 2003; 456: 260-266.