Figure 1.

Morphology and molecular phenotype of sensory neurons that innervate bone. The DRG soma of primary afferent neurons that innervate the bone marrow and periosteum are mostly small diameter myelinated and unmyelinated neurons with free fiber endings, although some larger neurons with encapsulated endings do exist in the periosteum. They express varying combinations of markers characteristic of nociceptive neurons, including calcitonin gene-related peptide (CGRP), substance P (SP) and the tyrosine receptor kinase A (TrkA), and/or bind isolectin B4 (IB4). IB4 binding has not been observed in peripheral nerve terminals (represented by dotted line).