A
nerve fiber is a threadlike extension of a
nerve cell and consists of an
axon and (in some cases) a
myelin sheath. There are nerve fibers in the
central nervous system and
peripheral nervous system. In the central nervous system (CNS), myelin is produced by
oligodendroglia cells.
Schwann cells form myelin in the peripheral nervous system (PNS). Schwann cells can also make a thin covering for an axon which does not consist of myelin (in the PNS). A peripheral
nerve fiber consists of an axon, myelin sheath, Schwann cells and its
endoneurium. There are no endoneurium and Schwann cells in the central nervous system.