Pacinian corpuscle · Lobeworks/17

The Pacinian corpuscle is a sensory receptor that detects vibration, a mechanoreceptor of the skin made of a nerve ending inside an onion of 20 to 70 fluid-separated layers, deep in the dermis and in joints and membranes, that fires at the onset and at the release of a pressure, falls silent while it is held, and answe

Pacinian corpuscle. The Pacinian corpuscle is a sensory receptor that detects vibration, a mechanoreceptor of the skin made of a nerve ending inside an onion of 20 to 70 fluid-separated layers, deep in the dermis and in joints and membranes, that fires at the onset and at the release of a pressure, falls silent while it is held, and answers best to vibration around 250 Hz.

Its rapid adaptation starts in the capsule. A sudden push deforms the layers all the way to the ending; a held push is taken up as the fluid-filled lamellae slide and redistribute it, so the ending in the middle stops being squeezed. Stripped of its capsule in the laboratory the ending becomes slowly adapting, the classic demonstration that the onion is a mechanical high-pass filter (the analog filter of electronics, built from tissue). The capsule is also chemical: its modified Schwann cells release GABA during a sustained push, which damps the ending (Pawson and colleagues, 2009).

Large fields, deep, few. Each corpuscle senses vibration over a whole region of the hand rather than a point, so it says that something buzzes and leaves the where to the smaller receptors near the surface.

What it is for in daily life. The phone vibrating in a pocket, the texture felt through a tool held in the hand, the bump of a pen touching the paper.

It rides an Aβ fibre, fast and myelinated like the other three skin receptors of touch, so its speed of conduction says nothing about its adaptation.

The onion is the filter.

Remove the layers and the same ending reports a steady push for as long as it lasts.

Questions: What makes the Pacinian corpuscle stop answering a pressure that is held? Mostly its capsule. The layers pass a quick deformation through to the ending in the middle but take up a steady one as they slide and redistribute it, so a held push stops reaching the ending; removed from its capsule, the same ending adapts slowly. The capsule's cells also release GABA during a sustained push, which damps the ending further, so the filter is partly chemical as well as mechanical.