Pacinian corpuscle

Pacinian corpuscle
Pacinian corpuscle, with its system of capsules and central cavity. a. Arterial twig, ending in capillaries, which form loops in some of the intercapsular spaces, and one penetrates to the central capsule. b. The fibrous tissue of the stalk. n. Nerve tube advancing to the central capsule, there losing its white matter, and stretching along the axis to the opposite end, where it ends by a tuberculated enlargement.
Pacinian capsule labeled at bottom.
Latin	corpusculum lamellosum
Gray's	subject #233 1060
MeSH	Pacinian+Corpuscles

Pacinian corpuscles are one of the four major types of mechanoreceptor. They are nerve endings in the skin, responsible for sensitivity to pain and pressure.

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^[1] .

The Pacinian corpuscle is oval 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 and are rapidly adapting (phasic) receptors. 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. ^[1] Their optimal sensitivity is 250 Hz and this is the frequency range generated upon finger tips by textures made of features smaller than 200 µms.^[2] 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 ^[1]. 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 ^[1]. They only sense stimuli that occur within this field.

How it works

Pacinian corpuscles sense stimuli due to the deformation of their rings of lamellae which press on the top of the sensory neuron. When the lamellae are deformed, either due to pressure or release of pressure, a generator potential is created as it physically deforms the plasma membrane of the tip of the neuron making it “leak” Na+ ions. If this potential reaches a certain threshold nerve impulses or action potentials are formed by pressure sensitive sodium channels at the first node of Ranvier, the first node of the myleinated sensory neuron. This impulse is now transferred along the axon with the use of sodium channels and sodium/potassium pumps in the axon membrane. As long as the top of the neuron is depolarized it will continue to depolarize the first node of Ranvier. It is a graded response meaning the greater the deformation the greater the generator potential. This information is encoded in the frequency of impulses as a bigger or faster deformation induces a higher impulse frequency. Action potentials are formed when the skin is rapidly distorted but not when pressure is continuous. The frequencies of the impulses decrease quickly and soon stop due to the layers of connective tissue that cover the nerve ending. This adaption is useful as it stops the nervous system from being overloaded with unnecessary information such as the pressure exerted by clothing.

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. ^[3]

Additional images

diagrammatic sectional view of the skin (magnified).

Schema (German)

light micrograph showing three corpuscles in the center of the field

References

See also

• List of human anatomical parts named after people.

External links

• Virginia Commonwealth University
• Anatomy Atlases - Microscopic Anatomy, plate 06.124
• lamellated+corpuscles at eMedicine Dictionary