In the peripheral nervous system, carry messages from special receptors in the skin, muscles, and other internal and external sense organs to the spinal cord, which sends them along to the brain. hormones motor nerves neuromodulators sensory nerves

Red blood cells are responsible for transporting oxygen in the blood. people with sickle cell anemia were born with a defective gene that results in sickle-shaped red blood cells. individuals with the disease often suffer pain in their extremities due to the build-up of these cells causing blockages in the blood vessels. the shape of the blood cells also reduces the amount of oxygen transported in the blood.