Neuroglia (glial cells)
Neuroglia
Also known as: glia, glial cells, neuroglial cells
The non-neuronal supporting cells of the nervous system. There are four types in the CNS (astrocytes, oligodendrocytes, microglia, ependymal cells) and two in the PNS (Schwann cells, satellite cells). They myelinate, nourish, protect and regulate neurons, and they keep the ability to divide.
Overview
Glia were once thought to outnumber neurons 10:1. Modern isotropic fractionator counts show a roughly 1:1 ratio in the human brain overall, with the proportion varying widely by region: high in white matter and the cortex, low in the cerebellum. They are far more than "glue" (Greek glia). Glia form myelin, maintain ion and neurotransmitter homeostasis, build and maintain the blood–brain barrier, guide neuronal migration during development, prune synapses, clear debris and mount the CNS immune response. They also signal to neurons, as in the tripartite synapse.
Glia arise from neuroectoderm, except microglia, which come from yolk-sac macrophage precursors. Unlike most neurons, glia retain the capacity to proliferate throughout life. As a result, most primary brain tumours are gliomas and arise from glial or glial-precursor cells. Glia also respond to injury: astrocytes proliferate and form a glial scar (gliosis), and microglia become activated.
Parts & subdivisions
- The most numerous CNS glia. Star-shaped, GFAP-positive. Their end-feet contribute to the blood–brain barrier; they buffer K⁺, recycle glutamate, supply lactate and form scars.
- Form CNS myelin. Each cell myelinates segments of up to ≈50 axons. Targeted in multiple sclerosis.
- Resident macrophages of the CNS, of yolk-sac (mesodermal) origin. They survey, phagocytose and prune synapses.
- Ciliated epithelium lining the ventricles and central canal. Modified ependyma forms the choroid plexus epithelium that secretes CSF.
- Myelinate one internode of one peripheral axon, or ensheathe many unmyelinated axons (Remak cells). Essential for peripheral nerve regeneration.
- Flattened cells encapsulating neuronal somata in sensory and autonomic ganglia. They are the PNS counterpart of astrocytes.
Anatomy
- Development
Radial glia are the neural stem cells of the developing cortex and the scaffold along which neurons migrate. They later give rise to astrocytes and ependyma. Oligodendrocytes develop from oligodendrocyte precursor cells (NG2 cells), which persist in the adult. Schwann and satellite cells derive from the neural crest. Microglia derive from yolk-sac erythromyeloid progenitors that colonise the brain early in embryogenesis.
Function
- Myelination: oligodendrocytes in the CNS, Schwann cells in the PNS.
- Homeostasis of K⁺, water, pH and neurotransmitters.
- Metabolic support of neurons (lactate shuttle, glycogen stores).
- Formation and maintenance of the blood–brain barrier.
- Immune defence and repair: microglia, reactive astrocytes, and Schwann cells in regeneration.
- Production and circulation of CSF (ependyma, choroid epithelium).
Clinical significance
Gliomas
The most common primary intra-axial brain tumours in adults. Glioblastoma (IDH-wildtype, WHO grade 4) is the most common malignant primary brain tumour. It shows pseudopalisading necrosis and microvascular proliferation, crosses the corpus callosum ("butterfly glioma"), and has a median survival of about 15 months. Others: oligodendroglioma (IDH-mutant, 1p/19q-codeleted), pilocytic astrocytoma (children, cerebellum) and ependymoma.
Test yourself
Which glial cell is derived from yolk-sac myeloid precursors rather than neuroectoderm, and acts as the resident macrophage of the CNS?
- Astrocyte
- Microglia
- Ependymal cell
- Oligodendrocyte
Answer: Microglia
Microglia colonise the brain early in embryonic life from yolk-sac erythromyeloid progenitors. They survey the brain, phagocytose debris, prune synapses and present antigen. All the other glia come from the neural tube or neural crest.
Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.