Bones are often perceived as rigid frameworks, but they are dynamic, living tissues constantly undergoing formation and breakdown. Many wonder if these seemingly hard structures possess nerves. The answer reveals a sophisticated biological system at play.
The Location of Nerves in Bone
The outer surface of bone is covered by the periosteum, a thin, fibrous membrane richly supplied with sensory and autonomic nerve fibers and blood vessels. From the periosteum, these nerve fibers and blood vessels enter the bone’s interior through small openings called nutrient foramina.
These foramina lead into nutrient canals, extending into the bone’s medullary cavity. Within compact bone, nerves also penetrate through Volkmann’s canals, which connect to Haversian canals. These microscopic canals run parallel to the bone’s long axis and contain capillaries and nerve fibers.
The Sensation of Bone Pain
Nerves within bone transmit pain sensations. This sensation is primarily mediated by specialized sensory nerves called nociceptors, which are small-diameter, thinly myelinated or unmyelinated fibers. These nociceptors are found in the periosteum and bone marrow, detecting harmful stimuli.
When a bone experiences trauma, such as a fracture, pain results from the tearing of the periosteum, activating these nociceptors. Inflammation from infections like osteomyelitis or tumors can also activate these sensory nerves through inflammatory mediators. Chemical signals, including growth factors or protons released during bone remodeling, can further trigger these pain receptors. Activated nerves then transmit signals to the spinal cord and brain, leading to bone pain perception.
Nerves’ Role in Bone Health and Repair
Beyond transmitting pain signals, the nervous system actively influences bone health and repair. Autonomic nerves, part of the peripheral nervous system, regulate blood flow within the bone, delivering nutrients and removing waste products. These nerves, specifically the sympathetic and parasympathetic divisions, coordinate the activities of cells responsible for bone remodeling.
Nerves also release signaling molecules, known as neuropeptides, which directly impact bone cells. For instance, neuropeptides like calcitonin gene-related peptide (CGRP) and substance P (SP) can influence osteoblasts, which are cells that form new bone, and osteoclasts, which resorb old bone. This regulatory function, through molecule release, plays a role in bone growth, remodeling, and fracture healing. Proper nerve function is essential for skeletal tissue repair and maintenance.