Bone is able to heal more rapidly than muscle or nerve tissue, because both muscle and nerve cells are relatively permanent, while bone is constantly remodeled by osteoblasts and osteoclasts, and thus can be repaired relatively rapidly. Bone building through increased secretion of osteoid is stimulated by the secretion of growth hormone by the pituitary, thyroid hormone and the sex hormones (estrogens and androgens).Osteoblasts can also be induced to secrete a number of cytokines that promote reabsorbtion of bone by stimulating osteoclast activity and differentiation from progenitor cells.Your muscles heal very differently than your bones. you fracture a bone, as long as it is set and fixed in place properly, it will tend to heal so thoroughly that it will become stronger than it was before the fracture! Your muscles however, do not actually heal with muscle tissue, but with "foreign" substances including collagen. The resulting scar tissue is weaker, less elastic, and highly prone to re-injury. Once a muscle is damaged, it can become the source of a great deal of pain. Muscle healing can require several months, and muscle scarring is often permanent. Nerve tissue healing is slowest, because nerve cells are not readily regenerated. The duration of the regenerative process varies and may require 6-18 months, depending on the length of the nerve and the site of the lesion. Although the commonly quoted regeneration rate is 1 mm/d, this figure varies considerably and can be used only as a rough estimate. Occasionally, very early signs of recovery may be present, which are thought to be due to so-called pioneer axons, which quickly navigate the pathway to the target tissue ahead of most nerve fibers
