CORPUSCLES OF PACINI: LOCATION, HISTOLOGY, FUNCTIONS - BIOLOGY - 2025

The Pacinian corpuscles, also known as lamellar corpuscles are each encapsulated mechanoreceptors found in the skin of many mammals and operating in response to different types of pressure and vibration.

According to some historical archives, the existence of the Pacini corpuscles was documented more or less in the 18th century, around 1741. However, it was the Italian anatomist Filippo Pacini, in 1835, who "rediscovered" them and led the attention from the scientific community to these structures, which were named in his honor.

Graphical scheme of a Pacini corpuscle (Source: Henry Vandyke Carter Via Wikimedia Commons)

Mechanoreceptors such as lamellar corpuscles are a type of sensory receptor that, in reality, corresponds to peripheral dendrite nerve endings specialized in the perception of stimuli and in the transmission of information to the central nervous system.

These are exteroceptors, as they are located mainly on the body surface and their function is to receive the very different environmental stimuli.

In some texts they are described as "kinesthetic" receptors, since they are involved in the maintenance of smooth and coordinated movements. Like other mechanoreceptors, these respond to stimuli that deform the tissues where they are.

Location

Pacini corpuscles have been found mainly in the deep portions of the skin tissue. They are found on the fingers of the hands and on the breasts of women, as well as in the connective tissue associated with the joints and the mesentery and legs.

They have also been described in the muscular layers of the face, in the pancreatic tissue, in some serous membranes and in the external genitalia and, where appropriate, these corpuscles are specifically located in the dermal and hypodermic layers of the skin.

Some authors suggest that these structures are also found in some of the regions of the temporal bone that are associated with the middle ear.

Histology

As mentioned at the beginning, the Pacini corpuscles are encapsulated mechanoreceptors in the skin. They are large structures with an oval appearance; in humans they are roughly 2-2.5 mm long and around 0.7 mm in diameter, so they would be easily recognizable with the naked eye.

These receptors are made up of an unmyelinated nerve fiber (myelin is an "insulating" layer that surrounds some nerve fibers and that contributes to increasing conduction speed), which is distributed throughout the internal length of its structure.

In the central portion of each Pacini corpuscle there is a nerve terminal (which is also not myelinated) surrounded by layers of fibroblast-like cells (modified fibroblasts).

Said nerve fibers associated with the corpuscles of Pacini are located together with the sensory fibers of mixed nerves, capable of innervating muscles, tendons, joints and also blood vessels.

The capsule of the corpuscles of Pacini

Covering these cell layers is the "capsule", which actually corresponds to a superficial layer of connective tissue that surrounds the entire corpuscular structure. The capsule has no part in the process of receiving stimuli or in their mechanical-electrical conversion.

However, this structure does function as the element that couples external stimuli with the sensor. Therefore, the characteristics of the sensory portion depend, to a great extent, on the mechanical properties of the coupling.

Some consider that, due to the histological arrangement of the cell layers, the section of a Pacini corpuscle resembles that of an onion when sliced.

The first works carried out regarding the structure of Pacini's corpuscles could provide indications that between each of the “lamellae” (the name given to the cell layers) there was a space filled with liquid and, furthermore, that each lamella it was connected to each other by a ligament at the distal pole of each corpuscle.

The liquid has been recognized as similar to lymph, with characteristics similar to those of water (at least in terms of viscosity and density), in which numerous collagen fibers are immersed.

Features

Lamellar corpuscles are "rapidly adapting" mechanoreceptors that are particularly specialized in receiving vibrational, touch, and pressure stimuli.

Graphic scheme of receptors in human skin: mechanoreceptors can be free or encapsulated receptors. Examples of free receptors are capillary receptors in the roots of hairs. The encapsulated receptors are the corpuscles of Pacini and the receptors in the glabrous (hairless) skin: the corpuscles of Meissner, the corpuscles of Ruffini and the disks of Merkel (Source: US-Gov Via Wikimedia Commons)

In the years immediately after their discovery, these corpuscles were associated with animal "magnetism" or mesmerism (a kind of therapeutic doctrine), so there was a lot of "occult" in relation to the function of these structures.

Some scientists of the time considered, then, to have discovered the scientific bases for the "imposition of hands and feet" (rich in Pacini corpuscles), widely practiced by supporters of mesmerism and that proposed that anyone could heal another through of magnetic interactions.

At present, however, it is known that these organs work by sending electrical signals to the central nervous system, signals that are the product of the conversion or translation of mechanical stimuli such as pressure and / or vibrations.

How do Pacini corpuscles work?

Pacini corpuscles have the function of perceiving mechanical stimuli, it must be remembered that they are mechanoreceptors, and converting them into electrical impulses that can be “interpreted” by the central nervous system when they are transported by neuronal axons.

The electrical responses, which are produced through the translation of mechanical signals, arise at the ends of the unmyelinated nerves found in the central portion of the lamellar corpuscles.

The mechanical energy of the stimulus is transmitted through the capsule, which corresponds to the fluid-filled lamellar structure that surrounds the "nucleus" of unmyelinated nerve ends, which is what functions as a transducer.

When the skin of the hand, for example, receives a mechanical stimulus that deforms the corpuscles of Pacini, the deformation of one lamella stimulates the deformation of the adjacent lamellae, since they are connected to each other through elastic portions such as tendons.

This deformation triggers the formation of action potentials that are transmitted to the nerve end and from which they pass to the brain, which promotes the global response to mechanical stimuli.

References

1. Bentivoglio, M., & Pacini, P. (1995). Filippo Pacini: a determined observer. Brain research bulletin, 38 (2), 161-165.
2. Cauna, N., & Mannan, G. (1958). The structure of human digital pacinian corpuscles (corpuscula lamellosa) and its functional significance. Journal of anatomy, 92 (Pt 1), 1.
3. Diamond, J., Gray, JAB, & Sato, M. (1956). The site of initiation of impulses in Pacinian corpuscles. The Journal of physiology, 133 (1), 54.
4. Loewenstein, WR, & Mendelson, M. (1965). Components of receptor adaptation in a Pacinian corpuscle. The Journal of physiology, 177 (3), 377-397.
5. Loewenstein, WR, & Skalak, R. (1966). Mechanical transmission in a Pacinian corpuscle. A Gussen, R. (1970). Pacinian corpuscles in the middle ear. The Journal of Laryngology & Otology, 84 (1), 71-76. Analysis and a theory. The Journal of physiology, 182 (2), 346-378.
6. Spencer, PS, & Schaumburg, HH (1973). An ultrastructural study of the inner core of the Pacinian corpuscle. Journal of neurocytology, 2 (2), 217-235.