Quick Facts
Oligodendrocytes are the non-neural cells of ectodermal origin forming part of the adventitial structure (neuroglia) of the central nervous system; projections of the surface membrane of each of these cells fan out and coil around the axon of many neurons to form myelin sheaths in the white matter. With microglia, they form the perineuronal satellites in the gray matter (Dorland, 2011).
Related parts of the anatomy
Structure and/or Key Features
Oligodendrocytes are the predominant neuroglia in the central nervous system (CNS). They are derived from the neural tube and when they migrate to their predestined location and mature, they can no longer divide.
Oligodendrocytes have a round nucleus and their cytoplasm contains a well-developed rough endoplasmic reticulum, numerous free ribosomes, numerous mitochondria, a Golgi complex, microtubules, and glycogen. In contrast to other glial cells, nuclei of oligodendrocytes appear heterochromatic rather than euchromatic and their cytoplasm is dense rather than pale. Additionally, they exhibit fewer branches and are smaller cells than astrocytes.
Oligodendrocytes produce the myelin sheath that wraps around axons of the CNS. They do this by extending processes towards one or several axons and wrapping its plasmalemma around the axon in concentric layers. In some regions of the CNS, oligodendrocytes can enclose up to fifty axons in separate myelin sheaths (Mancall and Brock, 2011). The area of the axon covered by the myelin sheath is called the internodal segments.
The internodal segments formed by the myelin sheaths becomes interrupted at regular intervals by the nodes of Ranvier, or myelin sheath gaps. The nodes of Ranvier are larger in the CNS than in the peripheral nervous system (PNS), and so, saltatory conduction is more efficient in the CNS. Oligodendrocytes and the axons they myelinate are not surrounded by a basement membrane (Splittgerber, 2018).
The equivalent cell type of oligodendrocytes in the PNS is the Schwann cell. However, Schwann cells can form myelin around a segment of one axon only (Mescher, 2013). Additionally, oligodendrocytes express different myelin-specific proteins during the process of myelination from Schwann cells in the PNS.
Oligodendrocytes also surround nerve cell bodies. The color of the white matter is attributed to myelin, the lipoprotein that is produced by oligodendrocytes. Unmyelinated axons in the CNS are often not embedded in glial cell processes (Mescher, 2013).
Function
Myelin sheaths act as an insulating covering that prevents electrical current from leaking from the axon. In addition, the myelin sheath increases the speed of conduction of nerve impulses (Marieb, Wilhelm and Mallatt, 2012).
Clinical Correlates
Deficiencies in any of the oligodendrocytes’ myelin-specific proteins seem related to demyelinating diseases of the CNS. Multiple sclerosis is characterized by demyelination in white matter of the CNS. The degenerated myelin sheaths are removed by microglial cells and then astrocytes proliferate to form a gliotic scar. Guillain-Barre syndrome is characterized by large segments of the myelin sheath being damaged in the PNS.
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Mancall, E. L. and Brock, D. G. (2011) Gray's Clinical Neuroanatomy: The Anatomic Basis for Clinical Neuroscience. Elsevier Health Sciences.
Marieb, E. N., Wilhelm, P. B. and Mallatt, J. (2012) Human Anatomy. fifth edn.: Benjamin Cummings.
Mescher, A. (2013) Junqueira's Basic Histology: Text and Atlas. 13th edn.: McGraw-Hill Education.
Splittgerber, R. (2018) Snell's Clinical Neuroanatomy. Wolters Kluwer Health.
