Understanding neuroanatomy, histology, and physiology are integral for medical students who are laying the foundation of neurology. For residents and fellows, reviewing such material serves as a refresher of topics not regularly confronted in clinical practice but are often seen on in-service and board examinations. In this section, we will cover CNS histology, anatomy as well as briefly mention some associated neurological syndromes.

Authors: James Eaton MD, Brian Hanrahan MD

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Central Nervous System Histology

Illustration and microscope slide with H&E stain showing glial cells and neurons
Illustration (left) and microscope slide with H&E stain (right) showing glial cells and neurons

Glial cells

  • Provide support and protection for neurons.
  • Glial cells outnumber neurons 10 to 1 in the central nervous system.

Astrocytes

  • The largest glial cell.
  • Support function of neurons in multiple ways:
    • Regulates interstitial fluid.
    • Modulates signals that regulate blood flow in response to neuronal activity.
    • Provides structural and nutritional support.
    • Remove excess glutamate from synapses.
    • Produce numerous angiogenic factors including VEGF.
      • VEGF decreases the stability of the blood-brain barrier with inflammatory conditions and CNS tumors.
  • Immunohistochemical staining for glial fibrillary acidic protein (GFAP) can be used to identify astrocytes.
    • Glial fibrillary acid proteins (GFAP) make up intracellular intermediate filaments located in astrocytic processes.

Microscopic images of astrocytes

Oligodendrocytes

  • Responsible for the formation of myelin in the central nervous system which provides electrical insulation.
  • Oligodendrocytes have condensed, rounded nuclei and unstained cytoplasm.
  • Myelinated fibers can be easily identified on microscopic slides with Luxol fast blue (LFB) staining.
    • The lack or paucity of LFB staining can suggest demyelinating disease.
  • Leukodystrophies typically involve metabolic and lysosomal pathways that are necessary for normal oligodendrocyte function.
  • Progressive Multifocal Leukoencephalopathy (PML) likely involves lytic infection of oligodendrocytes to induce demyelination.
  • Oligodendrogliomas are primary brain tumors with a classic ‘chicken wire’ appearance on histopathology.

Oligodendrocytes vs. Oligodendroglioma

Ependymal cells

  • Produces and facilitates the movement of cerebrospinal fluid (CSF).
  • Lines the ventricles and central canal of the spinal cord.
  • Resembles simple columnar epithelium with some cilia on histopathology.

Microglia

  • The primary immune cell of the central nervous system.
  • The smallest and rarest glial cell.
  • Derived from bone marrow/monocytes and enter the CNS in the perinatal period.
    • All other glial cells and neuronal cells are derived from neural tube cells.

Neuronal cells

  • Responsible for receiving, integrating, and propagating information to other cells.
  • Contains three parts; dendrites, cell body, and axon(s).
    • Dendrites
      • Receive information from other neurons at synapses.
      • Changes in dendritic spines are critical for neural plasticity that occurs during development and learning.
    • Cell body
      • The main synthetic and trophic center of the cell which contains the nucleus and most organelles.
      • Easily identified by a large central and euchromatic nucleus with a prominent nucleolus.
      • Basophilic clumps of polyribosomes are called Nissl bodies.
    • Axons
      • Conducts information to muscles, glands, or neurons.
      • Axons terminate at synapses.

Illustration and pathology slide of neuronal slides

Illustration and pathology slide of neurons

  • Most neurons contain multiple dendrites and only one axon.
  • Neurons can be easily identified with silver staining on microscopic slides which impregnate neurofilaments.
    • Intracellular neurofibrillary tangles can suggest a neurodegenerative disease such as Alzheimer’s.
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Table of Contents

Table of Contents