For people with a psychotic illness, or who have a predisposition to such an illness, the effects can be more serious and long-term. Psychotic illnesses are characterised by symptoms such as delusions, hallucinations and thought disorder. When people experience psychotic symptoms, they are unable to distinguish what is real â there is a loss of contact with reality. See also Factsheet 1: Psychosis.
Structure [edit]. Schwann cells are a variety of glial cell that keep peripheral nerve fibres (both myelinated and unmyelinated) alive. In myelinated axons, Schwann cells form the myelin sheath (see above). The sheath is not continuous.Individual myelinating Schwann cells cover about 100 micrometres of an axonâequating to approximately 10,000 Schwann cells along a 1 metre length of the axon.n this sense, Schwann cells are the peripheral nervous system's analogues of the central nervous system 's oligodendrocytes. However, unlike oligodendrocytes, each myelinating Schwann cell provides insulation to only one axon (see image).
myelin sheath. n. The insulating envelope of myelin that surrounds the core of a nerve fiber or axon and that facilitates the transmission of nerve impulses, formed from the cell membrane of the Schwann cell in the peripheral nervous system and from oligodendroglia cells. Also called medullary sheath.edullary sheath myelin sheath. myelin sheath (nerve sheath) the sheath surrounding the axon of myelinated nerve cells, consisting of concentric layers of myelin formed in the peripheral nervous system by the plasma membrane of Schwann cells, and in the central nervous system by the plasma membrane of oligodendrocytes.