Pacinian corpuscles
Summary
Pacinian corpuscles are encapsulated mechanoreceptors deep in the skin that detect vibration and deep pressure. They are rapidly adapting, so they fire at the start and end of a stimulus but very little during steady pressure.
Detail
Meaning: Pacinian corpuscles are mechanoreceptors, sensory endings that transduce mechanical force into electrical signals. A single axon ending is wrapped in onion-like layers of connective tissue, deep in the dermis and hypodermis (also in joints). Pressure or vibration deforms the ending, opening mechanically gated Na⁺ channels and producing a graded receptor potential; if it reaches threshold, action potentials fire. The layers pass rapid changes but not steady force, so the receptor adapts rapidly. They respond best to high-frequency vibration.
On the MCAT: Passages compare skin receptors: Meissner corpuscles (light touch, rapidly adapting), Merkel discs (sustained light touch, fine detail, slowly adapting), Ruffini endings (skin stretch, slowly adapting), and free nerve endings (pain, temperature). With constant pressure, a Pacinian corpuscle's firing rate falls quickly. Stronger stimuli raise action potential frequency and recruit more receptors; the size of each spike stays the same.
Common confusion: Deep pressure does not mean sustained pressure. Pacinian corpuscles signal the onset and offset of pressure and vibration; steady pressure is carried mainly by slowly adapting receptors such as Merkel discs and Ruffini endings. They are also not pain receptors.
Sources
- Campbell Biology
- Human Physiology: An Integrated Approach
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.