Cells involved in myelin formation around axons in peripheral nervous system are:

Astrocytes, which are found throughout the brain, are of two subtypes. Fibrous astrocytes, which contain many intermediate filaments, are found primarily in white matter. Protoplasmic astrocytes are found in gray matter and have a granular cytoplasm. Both types send processes to blood vessels, where they induce capillaries to form the tight junctions making up the blood-brain barrier. Ref: Ganong's Review of Medical Physiology 23rd edition, Chapter 4.