Neuroglia histology

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neuroglia types astrocyte oligodendrocyte microglia histology

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Here is a comprehensive overview of neuroglia histology based on Histology: A Text and Atlas with Correlated Cell and Molecular Biology:

Neuroglia — Histology

Neuroglia (supporting cells of nerve tissue) outnumber neurons by roughly 10:1. They differ from neurons in that they retain the capacity to divide throughout life. They are divided into peripheral neuroglia (PNS) and central neuroglia (CNS).

Key histologic point: In routine H&E preparations, only the nuclei of glial cells are visible. Heavy metal staining (e.g., silver impregnation) or immunocytochemistry (e.g., anti-GFAP antibody) is required to demonstrate the full cell morphology.

I. Central Neuroglia

There are four types of central neuroglia:

Distribution of all four glial cell types in brain tissue, showing astrocytes, oligodendrocytes, microglial cells, ependyma, neurons, and their spatial relationships to blood vessels and the pia mater

1. Astrocytes

The largest of the neuroglial cells. They form a network throughout the CNS and communicate with neurons to support and modulate many of their activities.

Two subtypes:

Feature	Protoplasmic Astrocytes	Fibrous Astrocytes
Location	Gray matter	White matter
Processes	Numerous, short, branching	Long, slender, unbranching
Filaments (GFAP)	Present (fewer)	Very numerous — hence the name
Function	Interact with up to 2 million synapses per cell; ion/neurotransmitter homeostasis	Structural support; cover nodes of Ranvier

Key functions:

Perivascular and perineural end-feet contribute to the blood-brain barrier (BBB)
Form the glia limitans — subpial foot processes contact the basal lamina of the pia mater, creating a relatively impermeable CNS boundary
Potassium spatial buffering: abundant K⁺ pumps and channels dissipate local K⁺ accumulation across their extensive process network
Confine neurotransmitters to the synaptic cleft; remove excess by pinocytosis
Phagocytic activity: eliminate unnecessary synapses during development and clear myelin debris after injury

Histologic marker: GFAP (glial fibrillary acidic protein) — the standard immunohistochemical marker for astrocytes.
Clinical note: Fibrous astrocytomas account for ~80% of adult primary brain tumors; identified microscopically and by GFAP positivity.

Protoplasmic astrocyte diagram showing perivascular feet terminating on a blood vessel (contributing to BBB), perineural feet on an axon, and a GFAP immunofluorescence image showing the full stellate morphology in green

2. Oligodendrocytes

Responsible for producing and maintaining the myelin sheath in the CNS.

Appear as small cells with relatively few, short processes in silver-stained or toluidine blue preparations
Often aligned in rows between myelinated fibers (interfascicular oligodendrocytes) or clustered around neurons (satellite oligodendrocytes / perineuronal satellites)
A single oligodendrocyte can myelinate up to 50 axons simultaneously (contrast with Schwann cells in the PNS, which myelinate only one axon segment each)
Myelin formed by concentric wrapping of oligodendrocyte plasma membrane processes around axons
Nucleus: round, dark, dense; cytoplasm stains more darkly than astrocytes

CNS vs. PNS myelination — key difference:

CNS: oligodendrocyte
PNS: Schwann cell (one cell → one internode on one axon)

3. Microglia

The resident immune cells of the CNS — the brain's macrophages.

Smallest of the neuroglia
Characteristic small, dark, elongated (rod-shaped) nuclei in routine stains
Cytoplasmic processes are short, irregular, and spine-bearing ("ramified" in resting state)
Phagocytic: remove cellular debris, dead neurons, and pathogens
Derived from mesodermal/monocyte lineage (not neuroectodermal — the exception among glia)
Upon injury → transform into activated macrophage-like cells (process retraction, cell body enlargement)

4. Ependymal Cells

Line the ventricular system of the brain and the central canal of the spinal cord.

Single layer of columnar to cuboidal epithelial-like cells
Apical surface bears both cilia and microvilli
Joined at their apical surfaces by junctional complexes (tight junctions + gap junctions)
Do not rest on a basal lamina (unlike true epithelium)

Specialized variants:

Tanycytes: found in the floor of the 3rd ventricle; lack cilia; long basal process projects into brain parenchyma; involved in transport of substances from CSF to the portal circulation of the hypothalamus; sensitive to glucose → may monitor energy balance
Choroid plexus epithelium: modified ependymal cells overlying capillary loops that produce CSF by active transport and secretion

II. Peripheral Neuroglia

1. Schwann Cells (Neurolemmocytes)

Three functional phenotypes:

Phenotype	Function
Myelinating Schwann cell	Wraps large-diameter axons; one cell → one internode on one axon
Non-myelinating Remak Schwann cell	Envelopes multiple small-diameter axons in cytoplasmic grooves → forms Remak bundles
Repair Schwann cell	Activated after nerve injury; dedifferentiate, form bands of Büngner, guide axon regrowth

Derived from neural crest cells under SOX10 transcription factor
Nucleus: oval, flattened, peripheral in the cell
Produce P0 protein (major structural myelin protein of PNS, unlike PLP/MBP in CNS)

2. Satellite Cells

Surround neuronal cell bodies in dorsal root ganglia, autonomic ganglia
Regulate the microenvironment around ganglion neurons
Flattened cells forming a capsule around each neuron cell body

3. Other Peripheral Neuroglia

Teloglia (terminal Schwann cells): cover axon terminals at the neuromuscular junction
Enteric glial cells: associated with ganglia in the wall of the alimentary canal (myenteric and submucosal plexuses)
Müller cells: radial glia of the retina

Summary Table

Cell Type	Location	LM Appearance	Key Marker	Primary Function
Protoplasmic astrocyte	CNS gray matter	Pale nucleus, short branching processes	GFAP	Synaptic support, K⁺ buffering
Fibrous astrocyte	CNS white matter	Pale nucleus, long slender processes	GFAP	BBB support, structural scaffold
Oligodendrocyte	CNS (white > gray)	Small, dark round nucleus, few processes	MBP, MOG	CNS myelination (up to 50 axons/cell)
Microglia	CNS	Small, dark, elongated nucleus; irregular processes	Iba1, CD68	Phagocytosis, immune surveillance
Ependymal cell	Ventricular lining	Columnar, cilia + microvilli apically	Vimentin, S100	CSF circulation, barrier
Schwann cell	PNS	Flattened nucleus, wraps axon	S100, P0	PNS myelination/support
Satellite cell	PNS ganglia	Flattened capsule around neuron	S100	Neuronal microenvironment

Source: Histology: A Text and Atlas with Correlated Cell and Molecular Biology (Wolters Kluwer, 9th ed.), Chapter 12 — Nerve Tissue

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