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Figure 1 | Orphanet Journal of Rare Diseases

Figure 1

From: Pathophysiology and medical treatment of pain in fibrous dysplasia of bone

Figure 1

Most sensory nerve fibers that innervate the bone express TrkA whereas fewer than 30% of the nerve fibers that innervate the skin express TrkA. The skin is innervated by thickly myelinated A-beta fibers (TrkA-), thinly myelinated A delta fibers (both TkA- and TrkA+), unmyelinated peptide-rich C fibers (TrkA+) and unmyelinated peptide-poor C-fibers (TrkA-). In contrast, the bone appears to be predominantly innervated by thinly myelinated A-delta fibers (TrkA- but mostly TrkA+) and peptide-rich C-fibers (mostly TrkA+ and a small proportion TrkA-). As greater than 80% of all sensory nerve fibers that innervate the bone are TrkA+ whereas only 30% of the sensory nerve fibers that innervate skin are TrkA+, these data might help explain why blocking NGF or its cognate receptor TrkA appears to be more efficacious in attenuating skeletal vs. skin pain.

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