Astrocytes and Oligodendrocytes
Astrocytes and oligodendrocytes are the two principal macroglial cells of the central nervous system. Astrocytes are star-shaped cells whose processes contact neurons, synapses, and blood vessels, maintaining the chemical and structural environment of the brain. Oligodendrocytes produce the myelin sheaths that insulate central axons, with a single oligodendrocyte myelinating segments of several axons. Together they account for much of the supportive tissue of the brain and spinal cord.
Definition
Astrocytes are star-shaped macroglial cells that support and regulate the neuronal microenvironment, while oligodendrocytes are macroglial cells that form the myelin sheaths of axons in the central nervous system.
Scope
This topic covers the histology and core biology of central macroglia: astrocyte morphology (protoplasmic and fibrous), the identification of astrocytes by glial fibrillary acidic protein, their roles at synapses and the vascular interface, and oligodendrocyte structure and the central myelination they provide. Peripheral myelination by Schwann cells is noted only for contrast. It is reference-educational and not clinical guidance.
Core questions
- How are protoplasmic and fibrous astrocytes distinguished, and where is each found?
- What roles do astrocytes play at the synapse and the vascular interface?
- How does a single oligodendrocyte myelinate central axons?
- What markers identify these cells histologically?
Key concepts
- Protoplasmic and fibrous astrocytes
- Glial fibrillary acidic protein (GFAP)
- Astrocyte end-feet
- Reactive astrogliosis
- Oligodendrocyte
- Central myelin and internodes
- Macroglia
Mechanisms
Astrocytes extend numerous processes that ensheath synapses, take up excess neurotransmitter and potassium, supply metabolic substrates, and place specialized end-feet on capillaries, where they contribute to the blood-brain barrier; they are identified by their intermediate filament protein GFAP and respond to injury by reactive astrogliosis (Sofroniew & Vinters, 2010; Bayraktar et al., 2014). Oligodendrocytes wrap layers of plasma membrane around axonal segments to form compact myelin, with one oligodendrocyte myelinating internodes on several different axons, and they also provide metabolic support to the axons they ensheath (Simons & Nave, 2015). Barres (2008) frames both cell types as active partners of neurons rather than passive support.
Clinical relevance
These cells are central to understanding demyelinating disease, gliosis and scar formation after central nervous system injury, and the origin of gliomas. This entry describes normal histology and cell biology for educational reference and is not a basis for diagnosis or treatment.
History
Golgi's silver methods first revealed glial cells alongside neurons, and Río-Hortega's specific staining in the 1920s distinguished oligodendroglia from astrocytes and microglia, establishing the modern classification of glia. The functional importance of astrocytes and oligodendrocytes was long underestimated; molecular and physiological studies reviewed by Barres (2008) and others recast them as active regulators of neural function and myelination.
Key figures
- Pío del Río-Hortega
- Camillo Golgi
- Ben A. Barres
Related topics
Seminal works
- sofroniew-2010
- simons-2015
- barres-2008
Frequently asked questions
- What is the difference between protoplasmic and fibrous astrocytes?
- Protoplasmic astrocytes have many short, branched processes and are found mainly in gray matter, while fibrous astrocytes have fewer, longer processes rich in intermediate filaments and predominate in white matter.
- How does central nervous system myelination differ from peripheral myelination?
- In the central nervous system a single oligodendrocyte myelinates internodes on several axons, whereas in the peripheral nervous system each Schwann cell myelinates a single internode of one axon.