Skip to main content
. Author manuscript; available in PMC: 2017 Jun 1.
Published in final edited form as: Pain. 2016 Jun;157(6):1239–1247. doi: 10.1097/j.pain.0000000000000514

Figure 4. Schematic illustrating the approximate percentage and types of TrkA and P2X3 expressing sensory nerve fibers that innervate the skin vs. bone.

Figure 4

The skin is innervated by thickly myelinated A-beta fibers (TrkA−, P2X3−), thinly myelinated A-delta fibers (TrkA−, P2X3−), unmyelinated peptide-rich C fibers (TrkA+, P2X3−) and unmyelinated peptide-poor C fibers (TrkA+, P2X3+). In contrast, the bone appears to completely lack any A-beta sensory nerve fibers and to be predominantly innervated by thinly myelinated A-delta fibers (TrkA+, P2X3−) and unmyelinated C fibers (TrkA+, P2X3−). In skin and bone there is also a small proportion (5% of the total) of unmyelinated C fibers (TrkA−, P2X3−). The percentages and types of sensory nerve fibers innervating the skin were estimated using data from previous studies (Bennett et al., 1996; Lu et al., 2001; Ambalavanar et al., 2005; Zylka et al., 2005) and for bone from the present and previous studies (Nakajima et al., 2008; Sugiura et al., 2008; Jimenez-Andrade et al., 2010). Note that the skin is heavily innervated by P2X3+ but not TrkA+ nerve fibers, where as the majority of sensory nerve fibers in bone are TrkA+ but not P2X3+.