The Five Senses and Beyond: The Encyclopedia of Perception - Jennifer L. Hellier 2017

Pacinian Corpuscles

Named for Italian anatomist Filippo Pacini (1812—1883), Pacinian corpuscles, also known as lamellar corpuscles, are one of the four major types of mechanoreceptors (touch receptors) found in the skin. They consist of free nerve endings within the skin that are responsible for sensitivity to vibration and pressure. These nerve endings respond to deformation by pressure or the removal of this pressure as might occur during vibrations. The sensitivity of the Pacinian corpuscles to pressure helps us to determine if a specific surface is smooth or rough. Pacinian corpuscles can also be found within the gut lining and joint capsules and play a role in proprioception, which is the ability to sense where joints and limbs are with respect to the rest of the body and in space. Pacinian corpuscles are especially sensitive to vibrations and are the primary skin receptor for vibration, specifically vibrations around 200 to 300 hertz (Hz).

Structure

Pacinian corpuscles look like tiny onions in the deeper layer of the skin, within the subcutaneous adipose tissue. They can also be found in joint capsules helping the brain sense and determine where the limbs are in relation to the rest of the body. Finally, Pacinian corpuscles are also located within the gut and help with visceral sensation. They are larger in size but fewer in number than Merkel cells and Ruffini corpuscles, other types of mechanoreceptors. They are approximately one millimeter in length and are encased in connective tissue. Pacinian corpuscles are modified Schwann cells (glial cells in the peripheral nervous system that produce myelin) and are very thin and flat. In the center of the corpuscles, there is a fluid-filled cavity with a single primary afferent (travels and sends a signal to the central nervous system), unmyelinated nerve ending. The primary afferent neuron is coated in layers of laminar cells, fluid-filled epithelial cells. Inside the corpuscle is a conduction structure called the first node of Ranvier, with a nerve sheath contained within. This nerve sheath is made of an electrically insulating myelin sheath. It is the deformation of these fluid-filled epithelial cells that initiates the electrical signal that transmits to the central nervous system.

Function

When a Pacinian corpuscle is deformed by pressure, the membrane allows sodium ions to “leak” out of the neuron. This causes a graded potential at the membrane, which is based on the strength of the stimulus creating the leakage. Every time pressure changes occur, a new graded potential is generated. These graded potentials reduce over time. If the sum of the graded potentials is high enough to reach membrane threshold, an action potential will be generated. This action potential is an all or nothing electrical signal. It is initiated in the nerve ending at the first node of Ranvier. The impulse from this action potential travels down the axon by causing sodium ion channels to open along the axon’s length. A sodium/potassium ion pump along with potassium ion channels will reset the membrane of the axon behind the action potential. The signal from the Pacinian corpuscle will travel along this primary afferent neuron to the spinal cord and then to the brain for processing.

Pacinian corpuscles have a large receptor field, meaning that they are capable of picking up sensations from a very large amount of area on the surface of the skin. Additionally, they are rapidly adapting, meaning that while they will quickly respond to a stimulus, that response does not last very long even if the stimulus persists. Once the pressure stimulus is removed, these corpuscles will send out another response.

Defects and Treatment

Although rare, a Pacinian corpuscle may develop a neuroma (tumor), as it is a free nerve ending. Other abnormal features are Pacinian corpuscle hyperplasia, which can be the precursor to a neuroma. In both cases, the patient will have extreme pain wherever the neuroma or hyperplasia is located. To date, the best treatment is surgery to remove the neuroma and then, in general, all symptoms are resolved.

Riannon C. Atwater and Renee Johnson

See also: Discriminative Touch; Mechanoreceptors; Meissner’s Corpuscles; Merkel Cell; Reflex; Sensory Receptors

Further Reading

Narayanamurthy, V. B., A. Thomas Winston, & Amit Gupta. (2005). A rare case of Pacinian corpuscle neuroma. Canadian Journal of Plastic Surgery, 13(1), 43—45. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3822480/

Purves, Dale, et al. (Eds.). (2001). Mechanoreceptors specialized to receive tactile information. In Neuroscience (2nd ed.). Sunderland, MA: Sinauer Associates. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK10895/