CNS histology

• Central Nervous System (CNS)

  Consists of the brain & spinal cord
• Brain


  • Brainstem
  • Cerebrum
  • Cerebellum

  
• Cells in the CNS

  • Neurons
  • Neuroglial cells (supporting cells)
• Types of neuroglial cells


  • Astrocytes (fibrous & protoplasmic)
  • Oligodendrocytes
  • Microglial cells
  • Ependymal cells

  
• Astrocytes


  • Provide structural support for CNS
  • Form a protective barrier limiting the penetration of substances into the CNS
  • Maintain the extracellular environment
  • Form a scar when injury occurs (reactive gliosis)

  
• Fibrous astrocytes


  Found predominantly in white matter, have numerous long, slender, infrequently branching cytoplasmic processes that run parallel to nerve fibres and terminate as expansions around blood vessels

  
• Protoplasmic astrocytes


  Mainly present in gray matter, have numerous short branching cytoplasmic processes that end feet surround nerve fibres and blood vessels

  
• Oligodendrocytes


  In white matter, form myelin sheaths around axons; in gray matter, form satellite cells around neuronal cell bodies

  
• Oligodendrocytes


  • Small cells with spherical, heterochromatic nuclei; have thin processes that surround CNS axons; have abundant rER, extensive Golgi complex, and many mitochondria
• Myelin sheath formation in CNS by oligodendrocytes

  1. Oligodendrocyte forms several processes, each contacting a different axon

  2. Process wraps around axon several times to form lamellae

  3. Cytoplasm is lost from the lamellae leading to contact of the inner surfaces of the cell membranes

  
• Microglial cells


  Resident macrophages of the CNS, have elongated, heterochromatic nuclei and numerous processes with many small branches
• Microglial cells


  • Have prominent Golgi complex, long cisternae of rER, lysosomes and lipofuscin

  
• Ependymal cells


  Form a protective barrier (zonulae occludens between cells) and produce cerebrospinal fluid (choroid plexus epithelium)
• Ependymal cells


  • Cuboidal or columnar cells lining the ventricles of the brain and central canal of the spinal cord, with motile cilia or microvilli on the surface facing the lumen

  
• Tanycytes


  Modified ependymal cells that line the walls of the 3rd ventricle and floor of the 4th ventricle, involved in the transport of substances between CSF in ventricles and blood in surrounding capillaries

  
• Tanycytes


  • Have microvilli on the luminal surface and an elongated process that extends into the hypothalamus and contacts capillaries and neurons

  
• White matter


  Formed by accumulations of myelinated axons, also contains supporting neuroglial cells and small blood vessels

  
• Gray matter


  Contains neuronal cell bodies, neuroglial cells, and neuropil (meshwork of axonal, dendritic and neuroglial processes)
• Typical neuron in cerebral cortex

  Has a pyramidal-shaped cell body with dendrites extending from the apex and basal edges, and an axon emerging from the central basal region

  
• Layers of cerebral cortex


  • Molecular layer
  • External granular layer
  • External pyramidal cell layer
  • Internal granular layer
  • Internal pyramidal layer
  • Fusiform (multiform) layer
• Hippocampus formation


  Involved in the processes of learning and memory
• Components of hippocampus formation

  • Hippocampus proper
  • Dentate gyrus
  • Subiculum
• Hippocampus proper


  Formed where the cerebral cortex is rolled into the lateral ventricle, curves around the thalamus
• Layers of hippocampus proper


  • Ventricular ependyma
  • Stratum alveus
  • Stratum oriens
  • Stratum pyramidale
  • Stratum radiatum
  • Stratum lacunosum
  • Stratum moleculare
• Stratum pyramidale


  Composed of small and large pyramidal neurons, with axons passing into the stratum alveus
• Dentate gyrus

  Contains a pyramidale cell (granular) layer and a polymorphous cell layer
• Cerebellum


  Co-ordinates voluntary movements and muscle function in the maintenance of normal posture
• Layers of cerebellar cortex


  • Molecular layer
  • Piriform/Purkinje layer
  • Granule cell layer
• Molecular layer


  Most superficial layer, composed of neuropil and basket cells
• Piriform/Purkinje layer


  Row of large piriform (Purkinje) neurons with dendrites forming dense tree-like structures in the molecular layer
• Granule cell layer


  Contains small, densely packed granule cells with heterochromatic nuclei
• Climbing fibres


  Terminal branches climb up the dendritic trees of piriform (Purkinje) neurons and synapse with them
• Mossy fibres


  Form terminal expansions in the granule cell layer that synapse with granule cell dendrites, forming synaptic complexes called glomeruli
• Regions of white matter in spinal cord


  • Dorsal funiculus
  • Lateral funiculus
  • Ventral funiculus