Ruffini ending · Lobeworks/17

The Ruffini ending is a sensory receptor that detects stretch of the skin, a mechanoreceptor made of a nerve ending woven through collagen in a small capsule of the dermis, which fires for as long as the skin around it is stretched, and is the receptor long credited with the SA2 signal of human touch.

Ruffini ending. The Ruffini ending is a sensory receptor that detects stretch of the skin, a mechanoreceptor made of a nerve ending woven through collagen in a small capsule of the dermis, which fires for as long as the skin around it is stretched, and is the receptor long credited with the SA2 signal of human touch.

Like the Merkel disc it is slowly adapting, but its fields are large and it answers to stretch rather than to indentation: the skin over the knuckles pulled taut as the fingers bend, a sideways drag on the palm. That makes it a source of the hand's sense of its own shape, alongside the muscle spindles, and of the direction of a force on an object held.

A biological strain gauge. It reads the deformation of a material it is bonded to, as the strain gauge of engineering does on a beam.

Its identity is not settled. SA2 fibres are recorded clearly in human skin, but Ruffini corpuscles are scarce in the fingertips, so whether every SA2 fibre ends in one is still open.

Tonic like Merkel, but coarse. It does not resolve shapes; it reports how the skin is pulled.

Ruffini feels the skin pulled, and keeps feeling it.

The hand learns how it is bent partly from how its own skin is stretched.

Questions: Merkel and Ruffini both keep firing under a steady stimulus: what does each one measure? Merkel measures indentation in fine detail: small fields near the surface that resolve edges, dots and texture, the system that reads Braille. Ruffini measures stretch of the skin: large fields deeper in the dermis that report how the skin is pulled, which tells the hand how its fingers are bent and which way an object pulls. Both are tonic; one draws the shape, the other feels the strain.