Pain receptors are specialized nerve endings located throughout the body in most body tissues. They transmit pain from injury, disease, movement or environmental stress. These specialized nerve endings are stimulated by release of pain producing chemicals that arise from local blood vessels, connective tissue cells called fibroblasts and specialized blood cells in the tissues called macrophages. Once the nerve endings are stimulated by these chemicals they begin firing the nerves that are connected to them and send pain signals to the spinal cord and brain.