A delta fibers and C fibers are categorized as nerve fibers that relay sensory information. They respond to pressure, temperature and pain. A delta fibers, however, are surrounded by a thin sheath of myelin. In the brain myelin is composed of Schwann cells while in the peripheral nervous system oligodendrocytes make up the myelin sheath. Myelin works as an insulator of nerve cells and allows them to relay messages at much faster speeds than unmyelinated cells. Therefore, the myelinated A delta fibers send sensory information to the brain at a much faster speed than the unmyelinated C fibers.