Page 628 - Concise Pathology for Exam Preparation ( PDFDrive )

23

The Central Nervous System

NORMAL CELLS OF THE CENTRAL NERVOUS SYSTEM (CNS)
AND THEIR CELLULAR MORPHOLOGY (FIG. 23.1)

Neurons

• They are organized as aggregates (nuclei and ganglia) or elongated columns/layers (eg, grey

o

column f spinal cord or six-layered cerebral cortex).

• They have a cell body (perikaryon), a large eccentric nucleus, prominent nucleolus and
abundant Nissl substance.
Glial Cells
• They form the supporting system for neurons and their dendritic and axonal processes.
• They play a role in inflammation, repair, fluid balance and energy metabolism.
Types
Macroglia
1.
These are derived from neuroectoderm and are of three main types:
(a)
Astrocytes
• They act like fibroblasts in response to injury (undergo hyperplasia and hyper-
trophy, termed ‘gliosis’)

• Astrocytic processes can be demonstrated by PTAH (phosphotungstic acid
haematoxylin) stain. Ultrastructurally, these processes are composed of abun-
dant intermediate filaments, mostly vimentin.
• Long-standing gliosis results in development of ‘Rosenthal fibres’, which are
eosinophilic elongated globular bodies present on astrocytic processes.
• Astrocytes are star shaped glial cells with long, highly branched processes. They
occupy most of the interneuronal space and mediate metabolic exchange. They
have the following sub-types:

(i) Fibrillary astrocyte: Long, thin processes; present mainly in the white matter.

(ii) Protoplasmic astrocyte
- Well-defined cytoplasmic margins and pyknotic nucleus
- Few cytoplasmic processes separated by minute spaces
(iii) Pilocytic astrocyte: Bipolar cells with long, thin, hair-like processes Glial
fibrillary acidic protein (GFAP)-positive
(iv) Gemistocytic astrocyte
- Soft, grey and swollen cell with eccentric nucleus/prominent nucleolus

- Abundant bright eosinophilic cytoplasm with stout cytoplasmic pro-

cesses
(b) Oligodendrocytes

(i) Moderate size

(ii) Small darkly staining nucleus with a clear halo around it

(iii) Small number of short-branched processes

(iv) Responsible for myelination of axons
(v) Predominant glial element in white matter

(vi) Aggregate closely around neurons in grey matter for support function (satellite

cells)
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