Morphologically, the Ruffini ending is similar to the Golgi tendon organ, it is a large (200–100 μm) and thin spindle-shaped cylinder composed

of layers of perineural tissue including Schwann cells and collagen fibers and an inner core composed of nerve terminals surrounded by a capsule space filled with fluid (Chambers et al., 1972 and Halata, 1977). In humans, each SAII axon possesses a low-threshold region, suggesting that a single Aβ fiber supplies each receptor organ (Johansson and Vallbo, 1980). Unlike the Merkel cell-neurite complex, the Aβ fibers that make up SAII-LTMRs are suggested to sense mechanical stretch applied to collagen fibers of the Ruffini ending (Maeda et al., 1999 and Rahman et al., 2011). It is unlikely, however, that in

the mouse Ruffini endings or Ruffini-like structures give rise to SAII-LTMR responses, as such structures have not been identified in rodents. Furthermore, rodent SAII-LTMRs have been observed Apoptosis inhibitor after stimulation of hairy skin in an ex vivo skin/nerve preparation in which deep structures such as muscles and associated joints are removed (Wellnitz et al., 2010 and Zimmermann et al., 2009). Therefore, the functions of SAII-LTMRs in different animal species and the morphological properties of SAII-LTMR endings remain unknown. The other physiologically defined mechanosensor is the RA receptor, which responds best to objects moving across the skin but less well to static indentation. As with SA-LTMRs, RA-LTMRs can be further divided into two categories: RAI- and RAII-LTMRs. In the simplest interpretation, (-)-p-Bromotetramisole Oxalate they merge into a psychophysical frequency Selleckchem Temsirolimus continuum, with RAI responses generally associated with small receptive fields and low-frequency vibrations, such as tapping and flutter (1–10 Hz), while RAII responses are associated with larger receptive fields and high-frequency vibrations (from 80–300 Hz) (Knibestol, 1973, Talbot et al., 1968 and Vallbo and Johansson, 1984). Anatomically, both are associated with corpuscles, which may be significant to both their rapidly adaptive properties and the tactile functions they subserve. RAI-LTMRs and Meissner Corpuscles. One of the hallmarks of rapidly adapting responses

is the firing of action potentials only at the initial and final contacts of a mechanical stimulus (Table 1). The percept initially associated with activation of RAI-LTMRs innervating the hand was the feeling of rapid skin movement or “flutter,” and, therefore, the first function ascribed to RAI-LTMRs was detection and scaling of low-frequency vibrations (Torebjörk and Ochoa, 1980). However, RAI-LTMRs possess other response properties that may be specialized for a unique function in grip control. First, in comparison to SAI-LTMRs, RAI-LTMRs are about four times more sensitive, yet respond with far less spatial acuity to stimuli moving across their receptive fields. Second, RAI-LTMRs respond consistently and with very short latencies to skin stimulation.