The structure and function of a slowly adapting touch corpuscle in hairy skin

Abstract

SUMMARY1. Slowly adapting cutaneous mechanoreceptors, in the cat and primates, have been studied by histological and neurophysiological methods.2. Each touch corpuscle is a dome-shaped elevation of the epidermis, whose deepest layer contains up to fifty specialized tactile cells.3. Nerve plates, enclosed by the tactile cell (Merkel cells), are connected to a single myelinated axon in the dense collagenous core of the corpuscle.4. The corpuscle generated > 1000 impulses/sec when excited by vertical surface pressure. The response was highly localized and showed a low mechanical threshold, the frequency being dependent upon' the velocity and amplitude of the displacement. There was a period of rapid adaptation before a sustained response which might continue for > 30 min.5. A quantitative analysis of the responses to excitation by displacements of differing amplitude, velocity and duration is included.6. The discharge of touch corpuscle units evoked by a mechanical stimulus was temperature-sensitive, and was enhanced by a fall in skin temperature.

Fine structure of Eimer's organ in the coast mole (Scapanus orarius)

“…The structure of the Merkel cell-neurite complexes in the coast mole appears very similar to that typically reported for Merkel cell-neurite complexes in many different species (Munger, 1965;Iggo and Muir, 1969;Andres and von During, 1973;Gottschaldt and VahleHinz, 1981;Munger and Ide, 1988). In particular, the Merkel cell-neurite complexes in the coast mole have prominent rod-like cytoplasmic extensions into surrounding keratinocytes and deeply lobulated nuclei.…”

“…7B and C). Given this, it is reasonable to suggest that they provide a slowly adapting SA-1 signaling component to the Eimer's organ receptor complex (Iggo and Muir, 1969;Gottschaldt and Vahle-Hinz, 1981). The circular arrangement of these receptors around the base of the central column, in conjunction with the presumably more rigid cells of the central column, may also provide these receptors with the ability to code for directional input as provided by differential pressure transmitted through the central column (Quilliam, 1966).…”

Quantitative Analyses of Dynamic Strain Sensitivity in Human Skin Mechanoreceptors

“…Second, cutaneous afferents that responded to a steady indenting force of 32 mN with a sustained discharge were classified as slowly adapting (SA), whereas afferents that responded only with on or on-and-off responses to indentation were classified as fast adapting (FA). Third, SA units were subdivided according to their discharge pattern during sustained indentation: afferents that showed irregular interspike intervals were classified as SAI (Chambers et al 1972;Edin 1992;Iggo and Muir 1969). The remaining SA units were subdivided into SAII and SAIII on the basis of their RFs and strain sensitivity: SAII units were those with ill-defined RF borders and strain sensitivity exclusively or predominantly in one direction, whereas SAIII units were characterized by sharp RF borders and largely omnidirectional strain sensitivity (Edin 2001).…”

Discharge patterns of the slowly adapting mechanoreceptor afferent units innervating the non-warty skin of the frog.

“…A similarity in response properties between SA type I units of mammals and SA units in the warty skin of frogs was indicated in the previous study . The receptors of the SA type I units in the hairy skin of mammals were identified as Merkel cells (IGGO and MUIR, 1969). Since numerous Merkel cells were also found in the frog skin (Fox and WHITEAR, 1978;NAFSTAD and BAKER, 1973), and Ft I units behave like SA type I units of the mammalian skin, Merkel cells might be the receptors of Ft I units.…”