[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Central nervous system](https://durgical.com/en/general-pathology/areas/cns/) › How brain cells react to injury

# How brain cells react to injury

- Lesion

Neurons cannot divide, so they show injury by shrinking, swelling or storing debris; astrocytes and microglia answer with scars and clusters.

Updated Nov 12, 2026

## Key points

- Red neuron: shrunken cell body, pyknotic nucleus, lost Nissl substance and bright eosinophilic cytoplasm; visible from about 6 to 12 hours after an irreversible hypoxic-ischemic insult.
- Axonal reaction (central chromatolysis): swollen round cell body, nucleus pushed to the edge, Nissl dispersed to the periphery, after axon damage.
- Gliosis is the brain's scar: hypertrophic astrocytes rich in GFAP, not fibroblasts and collagen.
- Microglial nodules with neuronophagia point to viral encephalitis; they are the brain's resident macrophages.
- Classic inclusions: neurofibrillary tangles (Alzheimer), Lewy bodies (Parkinson), Negri bodies (rabies), Cowdry bodies (herpes), owl-eye nuclei (CMV).

## What it is

The brain has a small set of cellular reactions that the pathologist reads like a vocabulary. Neurons turn shrunken and pink when they die acutely, round up when their axon is cut, and collect inclusions in degenerative, viral and storage diseases. Astrocytes proliferate and make a glial scar instead of collagen, and microglia gather into nodules around dying neurons. Recognising these patterns tells the type and the age of an injury.

## Structure

- Neurons: acute injury gives red neurons; chronic degeneration shows first as lost synapses, then neuron loss with reactive gliosis.
- Astrocytes: in gliosis the cell bodies enlarge and the cytoplasm turns pink (gemistocytes); long-standing scars are dense meshes of fine processes.
- Rosenthal fibres: thick, bright eosinophilic, corkscrew-shaped bodies in astrocyte processes of old gliosis and pilocytic astrocytoma.
- Corpora amylacea: round, layered, basophilic, PAS-positive bodies in astrocyte end-feet; more with age, no disease meaning.
- Alzheimer type II astrocytes: enlarged pale nuclei with marginated chromatin, typical of hyperammonemia (hepatic encephalopathy).
- Microglia: rod cells and nodules in infection; myelin-laden macrophages (foamy) clean up infarcts and demyelination.
- Ependyma: injury gives ependymal granulations, small bumps of glia under the lining, after ventriculitis such as CMV.

## Cellular reactions and what they usually mean

| Finding | Cell | Points to |
| --- | --- | --- |
| [Red (eosinophilic) neuron](https://durgical.com/en/conditions/perinatal-asphyxia-and-hypoxic-ischaemic-encephalopathy/) | Neuron | Acute irreversible injury: hypoxia, ischemia, hypoglycemia |
| Central chromatolysis | Neuron | Axon damage with attempted regeneration |
| [Neurofibrillary tangle, Lewy body](https://durgical.com/en/conditions/alzheimer-disease/) | Neuron | Neurodegenerative proteinopathy |
| [Negri, Cowdry, owl-eye inclusions](https://durgical.com/en/conditions/rabies/) | Neuron or glia | Rabies, herpes simplex or zoster, CMV |
| Gemistocytic gliosis | Astrocyte | Any injury: the brain's scar |
| [Alzheimer type II astrocyte](https://durgical.com/en/conditions/hepatic-encephalopathy/) | Astrocyte | High ammonia (liver failure) |
| [Microglial nodule, neuronophagia](https://durgical.com/en/conditions/viral-encephalitis/) | Microglia | Viral encephalitis, rickettsia, HIV |
| [Sheets of foamy macrophages](https://durgical.com/en/conditions/ischaemic-stroke/) | Microglia and blood macrophages | Resolving infarct, demyelination |

## Markers

- GFAP (astrocytes)
- Iba1, CD68 (microglia, macrophages)
- Neurofilament, NeuN (neurons)
- Ubiquitin, p62 (inclusions)
- PAS (corpora amylacea)

## Clinical notes

- Because mature neurons do not divide, even a small loss in a critical region gives a permanent deficit; recovery depends on surviving circuits.
- Groups of neurons that share metabolism or connections fail together (selective vulnerability), which is why diseases map to systems.

## Memory aid

Neurons turn red when they die, round when they regrow and full when they store; astrocytes scar, microglia gather.

## Test yourself

Think of the answer, then tap the question to see it.

## How soon after an irreversible hypoxic injury do red neurons appear?

From about 6 to 12 hours: the cell shrinks, the nucleus is pyknotic and the cytoplasm becomes intensely eosinophilic.

## What does the brain use instead of collagen to scar?

Reactive astrocytes: gliosis, a dense mesh of GFAP-positive glial processes.

## Which astrocyte change suggests hepatic encephalopathy?

Alzheimer type II astrocytes, with enlarged pale nuclei, caused by high ammonia.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/how-brain-cells-react-to-injury/)

[More Pathology questions →](https://durgical.com/en/practice/?f=pathology)

## Elsewhere in DurgiPedia

- [The neuron and synapse](https://durgical.com/en/histology/the-neuron-and-synapse/)
- [Glial cells: astrocytes, oligodendrocytes, microglia, Schwann cells](https://durgical.com/en/histology/glial-cells-astrocytes-oligodendrocytes-microglia-schwann-cells/)
- [Nerve injury and regeneration (Wallerian degeneration)](https://durgical.com/en/histology/nerve-injury-and-regeneration/)
- [Gray and white matter, cerebellar cortex, meninges](https://durgical.com/en/histology/gray-and-white-matter-cerebellar-cortex-meninges/)

## Connections

## Related 10

- [Global hypoxic-ischemic brain injury](https://durgical.com/en/general-pathology/global-hypoxic-ischemic-brain-injury/)
- [Cerebral infarction](https://durgical.com/en/general-pathology/cerebral-infarction/)
- [Neurodegeneration: the protein table](https://durgical.com/en/general-pathology/neurodegeneration-the-protein-table/)
- [Viral encephalitis: the shared pattern](https://durgical.com/en/general-pathology/viral-encephalitis-the-shared-pattern/)
- [Metabolic and toxic brain injury](https://durgical.com/en/general-pathology/metabolic-and-toxic-brain-injury/)
- [Patterns of necrosis: coagulative, liquefactive, caseous, fat, fibrinoid, gangrenous](https://durgical.com/en/general-pathology/patterns-of-necrosis-coagulative-liquefactive-caseous-fat-fibrinoid-gangrenous/)
- [Intracellular accumulations: cholesterol, proteins, hyaline, glycogen](https://durgical.com/en/general-pathology/intracellular-accumulations-cholesterol-proteins-hyaline-glycogen/)
- [Pigments in tissue: lipofuscin, hemosiderin, melanin, bilirubin, carbon](https://durgical.com/en/general-pathology/pigments-in-tissue-lipofuscin-hemosiderin-melanin-bilirubin-carbon/)
- [Endoplasmic reticulum stress and the unfolded protein response](https://durgical.com/en/general-pathology/endoplasmic-reticulum-stress-and-the-unfolded-protein-response/)
- [Peripheral nerve injury: axonal vs demyelinating](https://durgical.com/en/general-pathology/peripheral-nerve-injury-axonal-vs-demyelinating/)

## Related conditions 7

- [Ischaemic stroke](https://durgical.com/en/conditions/ischaemic-stroke/)
- [Perinatal asphyxia and hypoxic-ischaemic encephalopathy](https://durgical.com/en/conditions/perinatal-asphyxia-and-hypoxic-ischaemic-encephalopathy/)
- [Hepatic encephalopathy](https://durgical.com/en/conditions/hepatic-encephalopathy/)
- [Rabies](https://durgical.com/en/conditions/rabies/)
- [Parkinson disease](https://durgical.com/en/conditions/parkinson-disease/)
- [Alzheimer disease](https://durgical.com/en/conditions/alzheimer-disease/)
- [Viral encephalitis (herpes simplex encephalitis)](https://durgical.com/en/conditions/viral-encephalitis/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Brain Diseases | MedlinePlus](https://medlineplus.gov/braindiseases.html) (MedlinePlus, US National Library of Medicine, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/general-pathology/how-brain-cells-react-to-injury/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/how-brain-cells-react-to-injury/