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.