Demyelination is the major feature of Multiple Sclerosis. Which of the following cells forms myelin in the central nervous system?
The myelin sheath is formed by oligodendrocytes in CNS and by Schwann cells in the peripheral nervous system (PNS). The gaps formed between myelin sheath cells along the axons are called nodes of Ranvier. Since the lipid structure of myelin serves as a good insulator, the myelin sheaths increase the rate of propagation and efficacy of transmission of the impulse along the axon. The electrical impulse jumps from one node to the next at the rate as fast as 120 m/s. This rapid type of conduction is called saltatory conduction. Demyelination can occur early in life as consequence of congenital metabolic disorders. Demyelination later in life can be repaired with glia, which explains the frequent exacerbations and remissions in MS. It is believed that in MS, multiple mechanisms of immune injury of myelin coexist: cytokine-mediated injury of oligodendrocytes and myelin, digestion of surface myelin antigens by macrophages, complement-mediated injury, and direct injury by CD4+ and CD8+ T cells. This type of injury causes the loss of saltatory conduction in nerve fibers. The exposed axon is susceptible to fuher injury, resulting in irreversible axonal damage. Glial cells do not carry action potentials, but they have many impoant functions. There are several types of glial cells: astrocytes, which transpo nutrients to neurons, hold neurons in place, digest pas of dead neurons, and regulate the composition of extracellular space, and microglia, which possess phagocytic function, clean up debris, and protect the brain from microorganisms.Ependymal cells form the epithelial lining of the ventricle. Ref: Lomen-Hoeh C., Messing R.O. (2010). Chapter 7. Nervous System Disorders. In S.J. McPhee, G.D. Hammer (Eds), Pathophysiology of Disease, 6e.
Astrocytes
Ependymal cells
Microglia
OIigodendrocytes