Pacinian corpuscles are specialized sensory receptors located throughout the body, involved in touch. These structures act as biological transducers, converting mechanical stimuli into electrical signals that the brain can interpret. They detect specific touch sensations, aiding environmental perception.
Where Pacinian Corpuscles Are Located
Pacinian corpuscles are widely distributed, primarily found in the deeper layers of the skin, specifically the dermis and hypodermis. They are particularly abundant in sensitive areas such as the palms of the hands, soles of the feet, and fingertips, where tactile discrimination is important. Beyond the skin, these corpuscles are also found in various other tissues throughout the body. They are present around joints, within tendons, and in the periosteum, the membrane covering bones. Pacinian corpuscles also reside in some internal organs, including the mesenteries, breast, and genitals.
Their Unique Structure
Pacinian corpuscles possess a distinctive “onion-like” structure. Each corpuscle consists of 20 to 70 concentric layers, or lamellae, made of connective tissue. These layers surround a central core, which houses a single, unmyelinated nerve fiber. The lamellae are fluid-filled and encapsulated, forming a protective yet responsive casing around the nerve ending. This layered arrangement, resembling the cross-section of an onion, can measure up to 2 millimeters in length, making some visible to the naked eye.
What Sensations They Detect
Pacinian corpuscles are mechanoreceptors, primarily responsible for detecting high-frequency vibration and rapid changes in deep pressure. They excel at sensing transient mechanical disturbances rather than sustained pressure. For instance, they allow us to feel the distinct hum of an engine, the subtle vibration of a phone, or the texture of a surface as a finger quickly glides over it. These receptors are known for their rapid adaptation, meaning they respond strongly to the onset and offset of a stimulus but quickly cease firing if the stimulus remains constant. Their optimal sensitivity is around 250 Hz, a frequency range generated by fine textures.
How They Convert Touch into Signals
The conversion of mechanical touch into electrical signals, known as mechanotransduction, begins when external pressure or vibration deforms the Pacinian corpuscle’s outer lamellae. This deformation causes the concentric layers to shift, applying mechanical stress to the unmyelinated nerve ending at the core. The distortion of the nerve ending’s membrane opens specialized stretch-mediated ion channels, specifically sodium channels.
Once these channels open, positively charged sodium ions rush into the nerve ending, creating a localized electrical change called a graded receptor potential, also known as a generator potential. If this receptor potential reaches a specific threshold, it triggers an action potential, which is a rapid, self-propagating electrical impulse. This nerve impulse then travels along the neuron to the brain for interpretation. The rapid adaptation of Pacinian corpuscles occurs because the fluid within the lamellae quickly redistributes the pressure, allowing the nerve ending to return to its resting state even if the external stimulus persists.