Pacinian corpuscles

Pacinian corpuscles are one of the four major types of mechanoreceptor, responsible for sensitivity to deep pressure touch and high frequency vibration.

Location
These corpuscles are found in mesenteries, especially the pancreas, and are often found near joints.

Like Ruffini endings, they are found in deep subcutaneous tissue, and are considered rapidly adapting receptors, which means they will not fire action potentials throughout the duration of a stimulus but, rather, will fire briefly at its beginning and end (Kandel et al., 2000).

Structure
Similar in physiology to the Meissner's corpuscle, Pacinian corpuscles are larger and fewer in number than both Merkel cells and Meissner's corpuscles (Kandel et al., 2000).

The Pacinian corpuscle is ovoid shaped and approximately 1 mm in length. The entire corpuscle is wrapped by a layer of connective tissue. It has 20 to 60 concentric lamellae composed of fibrous connective tissue and fibroblasts, separated by gelatinous material. The lamellae are very thin, flat, modified Schwann cells. In the center of the corpuscle is the inner bulb, a fluid-filled cavity with a single afferent unmyelinated nerve ending.

Function
Pacinian corpuscles detect gross pressure changes and vibrations. Any deformation in the corpuscle causes action potentials to be generated, by opening pressure-sensitive sodium ion channels in the axon membrane. This allows sodium ions to influx in, creating a receptor potential.

These corpuscles are especially susceptible to vibrations, which they can sense even centimeters away (Kandel et al., 2000). Pacinian corpuscles cause action potentials when the skin is rapidly indented but not when the pressure is steady, due to the layers of connective tissue that cover the nerve ending (Kandel et al., 2000). It is thought that they respond to high velocity changes in joint position.

Pacinian corpuscles have a large receptive field on the skin's surface with an especially sensitive center (Kandel et al., 2000). They only sense stimuli that occur within this field.

Nomenclature
The Pacinian corpuscle was named after its discoverer, Italian anatomist Filippo Pacini.

The term "Golgi-Mazzoni corpuscle" (distinct from the Golgi organ) is used to describe a similar structure found only in the fingertips. 

Reference

 * Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science, 4th ed., p.433. McGraw-Hill, New York (2000). ISBN 0-8385-7701-6